First principles prediction of the solar cell efficiency of chalcopyrite materials AgMX 2 (M=In, Al; X=S, Se, Te)

Using the spectroscopic limited maximum efficiency, and Shockley and Queisser predictor models, we compute the solar efficiency of the chalcopyrites AgMX 2 (M = In, Al; X = S, Se, Te). The results presented are based on the estimation of the electronic and optical properties obtained from first principles density functional theory as well as the many-body perturbation theory calculations. The results from this report were consistent with the experimental data.The optical bandgap was accurately estimated from the absorption spectra, obtained by solving the Bethe and Salpeter equation. Fitting the Tauc's plot on the absorption spectra, we also predicted that the materials studied have a direct allowed optical transition. The theoretical estimations of the solar cell performance showed that the efficiencies from the Shockley and Queisser model are higher than those from the spectroscopic limited maximum efficiency model. This improvement is attributed to the absorption, the recombination processes and the optical transition accounted in the calculation of the efficiency.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, University of South Africa, University of Witwatersrand
Contributors: Dongho-Nguimdo, G. M., Igumbor, E., Zambou, S., Joubert, D. P.
Publication date: 1 Dec 2019
Peer-reviewed: Yes

Publication information

Journal: Computational Condensed Matter
Volume: 21
Article number: e00391
ISSN (Print): 2352-2143
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Materials Science (miscellaneous), Condensed Matter Physics, Materials Chemistry
Keywords: Chalcopyrites, First principles, Solar cell efficiency
Source: Scopus
Source-ID: 85065198754

Research output: Contribution to journalArticleScientificpeer-review

Recycling lithium mine tailings in the production of low temperature (700–900 °C) ceramics: Effect of ladle slag and sodium compounds on the processing and final properties

This paper deals with the valorization of quartz and felspar rich lithium mine tailings (QFS) in the development of construction materials. Ladle slag was used as green strength increasing agent. Sodium hydroxide and carbonate were used as fluxing agents to allow sintering at 700–900 °C. Of these, sodium hydroxide was found to be the more efficient. The sintered ceramics were characterized by X-ray diffraction, scanning electron microscopy, compressive test, water absorption, apparent density and dilatometry; the results were found to comply with ASTM C62-99 specifications for building brick, and interesting for a sustainable use of resources.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Research group: Ceramic materials, Tampere University of Technology, Univ of Oulu
Contributors: Lemougna, P. N., Yliniemi, J., Ismailov, A., Levänen, E., Tanskanen, P., Kinnunen, P., Roning, J., Illikainen, M.
Number of pages: 13
Pages: 332-344
Publication date: 10 Oct 2019
Peer-reviewed: Yes

Publication information

Journal: Construction and building materials
Volume: 221
ISSN (Print): 0950-0618
Original language: English
ASJC Scopus subject areas: Civil and Structural Engineering, Building and Construction, Materials Science(all)
Keywords: Building applications, Ceramic, Fluxing agent, Ladle slag, Lithium mine tailings, Sodium compounds
Source: Scopus
Source-ID: 85067302331

Research output: Contribution to journalArticleScientificpeer-review

Tribocorrosion behaviour of two low-alloy steel grades in simulated waste solution

The tribocorrosion behaviour of two low-alloy steels not previously investigated, was examined in a Pin-on-Disc test device, both in the presence and absence of mechanical wear and/or corrosion in simulated waste solution. Volume losses through wear, corrosion and synergy processes were calculated and changes in the material surfaces investigated. The tribocorrosion behaviour and the volume losses caused by the synergy processes were found to be dependent on the steel grade, instead of applied potential. For both steel grades, material losses were caused by two main degradation mechanisms: wear and wear-induced corrosion. Total material losses and the percentage of wear-corrosion synergy were higher for the ferritic grade than for the martensitic grade. These results are presented and discussed in this paper.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, VTT Technical Research Centre of Finland, Microscopy Center
Contributors: Mäntyranta, A., Heino, V., Isotahdon, E., Salminen, T., Huttunen-Saarivirta, E.
Number of pages: 13
Pages: 250-262
Publication date: 1 Oct 2019
Peer-reviewed: Yes

Publication information

Journal: Tribology International
Volume: 138
ISSN (Print): 0301-679X
Original language: English
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Surfaces and Interfaces, Surfaces, Coatings and Films
Keywords: Contact: sliding, Synergism: tribochemistry, Wear: corrosive

Bibliographical note

EXT="Heino, Vuokko"
EXT="Isotahdon, Elisa"

Source: Scopus
Source-ID: 85066497579

Research output: Contribution to journalArticleScientificpeer-review

Parametric study on temperature distribution of square hollow section joints

The resistance of a steel joint is one of the most crucial elements of a structure under fire conditions. The aim of the study was to investigate the temperature distribution within the square hollow section (SHS) joints with different geometric parameters under fire conditions. The commercial finite element (FE) software, Abaqus/Standard CAE, was used to simulate the behaviour of the SHS joints. Extensive numerical research was conducted on different joint types (T-, Y-, and K-joints) to examine the influence of the joint configuration on the temperature distribution within the joint. To provide reliable observations, a model was validated against the experimental results. The FE simulation results were compared to the predictions of Eurocode equations. The FE simulation results showed that the simulated temperatures are different from the temperatures determined using the Eurocode method. The β parameter was found to have hardly any influence on the temperature distribution within the joint area, whereas different joint configurations strongly influence the distribution.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Civil Engineering, Research group: Metal and Light-wight structures
Contributors: Bączkiewicz, J., Pajunen, S., Malaska, M., Heinisuo, M.
Number of pages: 9
Pages: 490-498
Publication date: 1 Sep 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Constructional Steel Research
Volume: 160
ISSN (Print): 0143-974X
Original language: English
ASJC Scopus subject areas: Civil and Structural Engineering, Building and Construction, Mechanics of Materials, Metals and Alloys
Keywords: Component method, Hollow section, Parametric study, Steel joint, Temperature distribution
Source: Scopus
Source-ID: 85067525966

Research output: Contribution to journalArticleScientificpeer-review

Porous polybutylene succinate films enabling adhesion of human embryonic stem cell-derived retinal pigment epithelial cells (hESC-RPE)

In the last decade, several studies have shown that polybutylene succinate (PBSu)has a high potential as a biomaterial enabling cell adhesion and growth. In this study, porous PBSu films have been prepared by the breath figure method (BF)and by particulate leaching (PL), and characterized in terms of thickness, surface properties, diffusion capacity and in vitro stability. Because porous films are of high interest for tissue engineering of retinal pigment epithelium (RPE), the initial viability and adhesion of human embryonic stem cell-derived RPE onto the PBSu films was then evaluated. To the best of our knowledge, this is the first study on the adhesion behavior of hESC-RPE onto porous and biodegradable polymer surfaces. The results clearly demonstrated that the two manufacturing methods produced materials with very distinct properties. Films produced by BF expressively demonstrated the highest roughness and surface area, and the lowest water contact angle. These features likely contributed to increase the biocompatibility of the surface, particularly when coated with laminin and collagen IV, as observed by the improved cell viability, cell morphology, adhesion and production of extracellular matrix proteins. Altogether, our results showed not only that PBSu holds high potential in retinal tissue engineering, but also that the physical properties and biocompatibility of the material are highly dependent on the adopted casting method.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Tampere University, Tampere University Hospital
Contributors: Calejo, M. T., Haapala, A., Skottman, H., Kellomäki, M.
Number of pages: 10
Pages: 78-87
Publication date: 1 Sep 2019
Peer-reviewed: Yes

Publication information

Journal: European Polymer Journal
Volume: 118
ISSN (Print): 0014-3057
Original language: English
ASJC Scopus subject areas: Physics and Astronomy(all), Polymers and Plastics, Organic Chemistry, Materials Chemistry
Keywords: Biodegradable films, Breath figures, Cell adhesion, Polybutylene succinate, Retinal pigment epithelium
Source: Scopus
Source-ID: 85066269398

Research output: Contribution to journalArticleScientificpeer-review

Characterizing the micro-impact fatigue behavior of APS and HVOF-sprayed ceramic coatings

The fatigue life of thermally sprayed Al2O3- and Cr2O3-based coatings has been studied under low-energy (0.7–5 mJ) impact conditions. A threshold impact energy and amount of repetitions the coatings can endure with said energy before catastrophic failure was obtained. The catastrophic failure was determined to occur when the fracture mode of the coating switched from brittle cone cracking to quasi-plastic radial cracking. The results are examined relative to the microstructural features along with other properties of the coatings - hardness and cavitation resistance. The experiment provided a new approach for a straightforward comparison of the micro-scale impact fatigue life of thermally sprayed coatings unachievable with previous methods.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Université Bourgogne Franche-Comté - ICB - UTBM - LERMPS
Contributors: Kiilakoski, J., Langlade, C., Koivuluoto, H., Vuoristo, P.
Pages: 245-254
Publication date: 15 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Surface and Coatings Technology
Volume: 371
ISSN (Print): 0257-8972
Original language: English
ASJC Scopus subject areas: Chemistry(all), Condensed Matter Physics, Surfaces and Interfaces, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Ceramic coating, Characterization, Fracture, Impact test, Surface fatigue, Thermal spray
Electronic versions: 
Source: Scopus
Source-ID: 85055977332

Research output: Contribution to journalArticleScientificpeer-review

Elevated and cryogenic temperature micropillar compression of magnesium–niobium multilayer films

The mechanical properties of multilayer films consisting of alternating layers of magnesium and niobium are investigated through micropillar compression experiments across a broad range of temperatures. The data collected from the variable temperature micropillar compression tests and strain rate jump tests are used to gain insight into the operative deformation mechanisms within the material. At higher temperatures, diffusion-based deformation mechanisms are shown to determine the plastic behavior of the multilayers. Diffusion occurs more readily along the magnesium–niobium interface than within the bulk, acting as pathway for magnesium diffusion. When individual layer thicknesses are sufficiently small, diffusion can remain the dominant deformation mechanism down to room temperature. Multilayer strengthening models historically rely solely on dislocation-based arguments; therefore, consideration of diffusion-based deformation in nanolaminates with low melting temperature components offers improved understanding of multilayer behavior.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Swiss Federal Laboratories for Materials Science and Technology, HCI e 486.1, University of California, Santa Barbara, University of Nevada, Reno, University of Minnesota Twin Cities
Contributors: Thomas, K., Mohanty, G., Wehrs, J., Taylor, A. A., Pathak, S., Casari, D., Schwiedrzik, J., Mara, N., Spolenak, R., Michler, J.
Number of pages: 18
Pages: 10884-10901
Publication date: 15 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Materials Science
Volume: 54
Issue number: 15
ISSN (Print): 0022-2461
Original language: English
ASJC Scopus subject areas: Materials Science(all), Mechanics of Materials, Mechanical Engineering
Source: Scopus
Source-ID: 85065435834

Research output: Contribution to journalArticleScientificpeer-review

Fluorine losses in Er 3+ oxyfluoride phosphate glasses and glass-ceramics

Er 3+ doped phosphate glasses with the composition 75NaPO 3- 25CaF 2 (mol%)were prepared at different melting temperatures to demonstrate the importance to quantify the fluorine content when preparing oxyfluoride glasses. Indeed, increasing the melting temperature from 900 to 1000 °C leads to a small reduction in the fluorine content from 9.4 at % to 8.8 at % as quantified using EPMA. Whereas this loss of fluorine can be suspected from small changes in the thermal properties of the glass, it increases significantly the glass crystallization tendency in this glass system. This means that a heat treatment of the as-prepared glass should be performed when evaporation of fluorine during the glass melting is suspected. Sample preparation for the characterization of the spectroscopic properties of the glasses is discussed here as well; bulk glasses should be used when measuring the spectroscopic properties of oxyfluoride glasses, which are known to be hygroscopic. It is shown, in this work, that a heat treatment of the glass within the investigated glass system leads to transparent glass-ceramics with volume precipitation of Er 3+ doped CaF 2 crystals with strong upconversion.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Materials Characterization, Materials Science and Environmental Engineering, Physics, Tampere University of Applied Sciences, Fondazione LINKS – Leading Innovation & Knowledge for Society
Contributors: Szczodra, A., Mardoukhi, A., Hokka, M., Boetti, N. G., Petit, L.
Number of pages: 7
Pages: 797-803
Publication date: 15 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Alloys and Compounds
Volume: 797
ISSN (Print): 0925-8388
Original language: English
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Metals and Alloys, Materials Chemistry
Keywords: Crystal, Erbium, Fluorine, Glass, Glass-ceramic, Luminescence
Source: Scopus
Source-ID: 85065824926

Research output: Contribution to journalArticleScientificpeer-review

3-D mechanical modeling of 20 T HTS clover leaf end coils - Good practices and lessons learned

Very high electromagnetic forces are generated in the superconducting coils of high field accelerator magnets. The cables, which are used to wind the coils, can withstand limited pressure levels and strains generated during the powering without degradation. To protect the cables from mechanical damage, reliable prediction of strain and stress inside the coil is paramount for designing suitable support structure of the magnet. This is naturally done before a magnet is built and tested, which emphasizes the need for reliable modeling. Conventionally, the mechanics in superconducting coils are modeled assuming homogenized material properties inside a homogenized coil volume. Using this so-called coil block approach, predicting the actual cable strain or stress inside the homogenized volume is unreliable. In order to predict reliably the stress in the cable, more detailed representation of the modeling domain is needed. This paper presents a workflow to perform a detailed mechanical analysis using finite-element analysis following the envisioned and more detailed approach. As an example, a high field 20 T+ magnet with clover leaf ends is studied, and results are discussed. The results reveal considerable difference between the behavior of modeled homogenized coil blocks and coils where turns are individually considered.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, European Organization for Nuclear Research
Contributors: Murtomäki, J. S., Van Nugteren, J., Stenvall, A., Kirby, G., Rossi, L.
Publication date: 1 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 29
Issue number: 5
Article number: 8642381
ISSN (Print): 1051-8223
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Accelerator magnets: dipoles, computer aided engineering, correctors, finite element methods, HTS magnets, magnet structure, magnet supports, modeling, quadrupoles, simulation, stress, superconducting magnet mechanical factors
Source: Scopus
Source-ID: 85065098308

Research output: Contribution to journalArticleScientificpeer-review

Exploration of Two Layer Nb 3 Sn Designs of the Future Circular Collider Main Quadrupoles

The goal of this study is to propose an alternative FCC quadrupole design where the risk from both their fabrication and their operation in the machine is reduced compared to previous analysis. Therefore, the number of coil layers has been reduced from four to two and the load-line margin has been increased from 14% to 20% compared to previous investigations ('Design of a Nb3Sn 400 T/m quadrupole for the future circular collider,' IEEE Trans. Appl. Supercond., vol. 28, no. 3, p. 4004905, Apr. 2018). Indeed, the idea is to only challenge the ∼5000 FCC main dipoles and stay at a relatively low complexity for the ∼700 FCC main quadrupoles so they have a limiting impact on the machine operation and reliability. An exploration of the strand diameter (0.7-0.9 mm), the cable size (40-60 strands), as well as the protection delay (30-40 ms) is performed on two-dimensional (2-D) magnetic designs of the FCC main quadrupole. A discussion on cable windability allows for the selection of one design generating 367 T/m. The design is mechanically constrained with a conventional collar structure leading to collaring peak stress of 115 MPa. A single coupling-loss-induced quench unit ensures a safe magnet operation with a 300 K hotspot temperature.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, IRFM, European Organization for Nuclear Research
Contributors: Lorin, C., Fleiter, J., Salmi, T., Schoerling, D.
Publication date: 1 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 29
Issue number: 5
Article number: 4001005
ISSN (Print): 1051-8223
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: collar structure,CLIQ protection system, MQ, Nb Sn coil
Source: Scopus
Source-ID: 85061237007

Research output: Contribution to journalArticleScientificpeer-review

Highly efficient charge separation in model Z-scheme TiO2/TiSi2/Si photoanode by micropatterned titanium silicide interlayer

Atomic layer deposited (ALD) TiO2 is an attractive material for improving the photoactivity and chemical stability of semiconductor electrodes in artificial photosynthesis. Using photoelectrochemical (PEC) measurements, we show that an interfacial, topographically microstructured TiSi2 layer inside the TiO2/Si heterojunction improves the charge carrier separation and shifts the water dissociation onset potential to more negative values. These observations are correlated with the X-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS) measurements, which reveal an increased band bending due to the TiSi2 interlayer. Combined with the UV–Vis absorption results, the photoelectron spectroscopy measurements allow the reconstruction of the complete energy band diagram for the TiO2/TiSi2/Si heterojunction and the calculation of the valence and conduction band offsets. The energy band alignment and improvements in PEC results reveal that the charge transfer across the heterojunction follows a Z-scheme model, where the metal-like TiSi2 islands act as recombination centers at the interface.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Surface Science, Physics
Contributors: Hannula, M., Ali-Löytty, H., Lahtonen, K., Saari, J., Tukiainen, A., Valden, M.
Number of pages: 9
Pages: 237-245
Publication date: 1 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Acta Materialia
Volume: 174
ISSN (Print): 1359-6454
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Polymers and Plastics, Metals and Alloys
Keywords: Electrochemical characterization, Electronic band structure, Titanium dioxide, Transition metal silicides, X-ray photoelectron spectroscopy (XPS)
Source: Scopus
Source-ID: 85066305210

Research output: Contribution to journalArticleScientificpeer-review

Erosion wear performance of WC-10Co4Cr and Cr 3 C 2 -25NiCr coatings sprayed with high-velocity thermal spray processes

Thermally sprayed hardmetal coatings are widely used to protect components and surfaces against wear in various applications. Hard and wear resistant coatings increase the component lifetime and can generate significant savings promoting ecological manufacturing. This study focuses on the performance of tungsten carbide (WC-10Co4Cr)and chromium carbide (Cr 3 C 2 -25NiCr)based hardmetal coatings sprayed with gaseous and liquid fuelled high-velocity oxygen-fuel (HVOF)spray processes and a modern high-velocity air-fuel (HVAF)spray process. The coating characterisation revealed reduced carbide dissolution with decreasing process temperature and denser feedstock powder particles. Smaller carbide size in the Cr 3 C 2 -25NiCr material significantly reduced the carbide rebounding leading to higher carbide content in the sprayed coating and improved erosion wear resistance. Most significant improvements were observed in cavitation erosion for HVAF sprayed WC-10Co4Cr coatings (0.4 μm/h)compared to the HVOF sprayed coatings (1.5–3.7 μm/h). The cavitation erosion resistance of the HVAF sprayed coatings was almost at the level of the WC-10Co sintered bulk (0.2 μm/h).

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Tampere University, VZÚ Plzeň - Research and Testing Institute
Contributors: Matikainen, V., Rubio Peregrina, S., Ojala, N., Koivuluoto, H., Schubert, J., Houdková, Vuoristo, P.
Number of pages: 17
Pages: 196-212
Publication date: 25 Jul 2019
Peer-reviewed: Yes

Publication information

Journal: Surface and Coatings Technology
Volume: 370
ISSN (Print): 0257-8972
Original language: English
ASJC Scopus subject areas: Chemistry(all), Condensed Matter Physics, Surfaces and Interfaces, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Cavitation erosion, Coating, Hardmetal, Slurry erosion, Thermal spray

Bibliographical note

INT=msee,"Rubio Peregrina, S."

Source: Scopus
Source-ID: 85065223119

Research output: Contribution to journalArticleScientificpeer-review

An architectural understanding of natural sway frequencies in trees

The relationship between form and function in trees is the subject of a longstanding debate in forest ecology and provides the basis for theories concerning forest ecosystem structure and metabolism. Trees interact with the wind in a dynamic manner and exhibit natural sway frequencies and damping processes that are important in understanding wind damage. Tree-wind dynamics are related to tree architecture, but this relationship is not well understood. We present a comprehensive view of natural sway frequencies in trees by compiling a dataset of field measurement spanning conifers and broadleaves, tropical and temperate forests. The field data show that a cantilever beam approximation adequately predicts the fundamental frequency of conifers, but not that of broadleaf trees. We also use structurally detailed tree dynamics simulations to test fundamental assumptions underpinning models of natural frequencies in trees. We model the dynamic properties of greater than 1000 trees using a finite-element approach based on accurate three-dimensional model trees derived from terrestrial laser scanning data. We show that (1) residual variation, the variation not explained by the cantilever beam approximation, in fundamental frequencies of broadleaf trees is driven by their architecture; (2) slender trees behave like a simple pendulum, with a single natural frequency dominating their motion, which makes them vulnerable to wind damage and (3) the presence of leaves decreases both the fundamental frequency and the damping ratio. These findings demonstrate the value of new three-dimensional measurements for understanding wind impacts on trees and suggest new directions for improving our understanding of tree dynamics from conifer plantations to natural forests.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, University of Oxford, SCION, University of Connecticut, Delft University of Technology, Wageningen University and Research Centre, University of Massachusetts Amherst, National Parks Board, University of Melbourne, Oregon State University, Universiteit Gent, National Physical Laboratory, University College London, NERC National Centre for Earth Observation (NCEO), 16 Center for International Forestry Research (CIFOR), Swedish University of Agricultural Sciences, INRA
Contributors: Jackson, T., Shenkin, A., Moore, J., Bunce, A., van Emmerik, T., Kane, B., Burcham, D., James, K., Selker, J., Calders, K., Origo, N., Disney, M., Burt, A., Wilkes, P., Raumonen, P., Gonzalez de Tanago Menaca, J., Lau, A., Herold, M., Goodman, R. C., Fourcaud, T., Malhi, Y.
Number of pages: 1
Publication date: 28 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of the Royal Society. Interface
Volume: 16
Issue number: 155
ISSN (Print): 1742-5689
Original language: English
ASJC Scopus subject areas: Biotechnology, Biophysics, Bioengineering, Biomaterials, Biochemistry, Biomedical Engineering
Keywords: finite-element analysis, fundamental frequency, natural frequencies, terrestrial laser scanning, tree architecture, wind damage
Source: Scopus
Source-ID: 85067464325

Research output: Contribution to journalArticleScientificpeer-review

Water-Responsive and Mechanically Adaptive Natural Rubber Composites by in Situ Modification of Mineral Filler Structures

A new biomimetic stimuli-responsive adaptive elastomeric material, whose mechanical properties are altered by a water treatment is reported in this paper. This material is a calcium sulphate (CaSO4) filled composite with an epoxidized natural rubber (ENR) matrix. By exploiting various phase transformation processes that arise when CaSO4 is hydrated, several different crystal structures of CaSO4·xH2O can be developed in the cross-linked ENR matrix. Significant improvements in the mechanical and thermal properties are then observed in the water-treated composites. When compared with the untreated sample, there is approximately 100% increase in the dynamic modulus. The thermal stability of the composites is also improved by increasing the maximum degradation rate temperature by about 20 °C. This change in behavior results from an in situ development of hydrated crystal structures of the nanosized CaSO4 particles in the ENR matrix, which has been verified using Raman spectroscopy, transmission electron microscopy, atomic force microscopy, and X-ray scattering. This work provides a promising and relatively simple pathway for the development of next generation of mechanically adaptive elastomeric materials by an eco-friendly route, which may eventually also be developed into an innovative biodegradable and biocompatible smart polymeric material.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Leibniz-Institut für Polymerforschung Dresden E.V., University of Massachusetts Lowell, Vodafone Department of Mobile Communications Systems, Queen Mary University of London
Contributors: Banerjee, S. S., Hait, S., Natarajan, T. S., Wießner, S., Stöckelhuber, K. W., Jehnichen, D., Janke, A., Fischer, D., Heinrich, G., Busfield, J. J., Das, A.
Number of pages: 8
Pages: 5168-5175
Publication date: 20 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry B
Volume: 123
Issue number: 24
ISSN (Print): 1520-6106
Original language: English
ASJC Scopus subject areas: Physical and Theoretical Chemistry, Surfaces, Coatings and Films, Materials Chemistry
Source: Scopus
Source-ID: 85067653290

Research output: Contribution to journalArticleScientificpeer-review

Epitaxial phases of high Bi content GaSbBi alloys

GaSbBi alloys have recently emerged as attractive materials for mid-infrared optoelectronics owing to strong band gap reduction enabled by Bi incorporation into the GaSb matrix. The fundamental understanding of the epitaxial process required to demonstrate high quality crystals is in an early-developmental phase. From this perspective, we report on the key role played by the Sb/Ga flux ratio in controlling the structural quality and incorporation of high Bi content GaSbBi (up to 14.5%-Bi), revealing three distinct epitaxial phases. The first phase (below stoichiometric Sb/Ga) exhibits Ga-Bi compound droplets, low crystal quality, and reduced Bi content. At the second phase (above stoichiometric Sb/Ga), the crystal exhibits smooth surfaces and excellent crystallinity with efficient Bi incorporation. The last phase corresponds to exceeding a Sb/Ga threshold that leads to reduced Bi incorporation, Bi droplets and degraded crystallinity. This threshold value that defines the optimal growth window is controlled by the temperature as well as the Bi/Ga ratio. Increasing temperature increases the threshold, albeit simultaneously reducing Bi incorporation. Conversely, increasing the Bi/Ga flux ratio increases Bi incorporation, while narrowing down and ultimately closing the window. This study provides a general framework enabling development of high quality GaSbBi heterostructures for emerging mid-infrared optoelectronics.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: ORC
Contributors: Hilska, J., Koivusalo, E., Puustinen, J., Suomalainen, S., Guina, M.
Number of pages: 5
Pages: 67-71
Publication date: 15 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Crystal Growth
Volume: 516
ISSN (Print): 0022-0248
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Inorganic Chemistry, Materials Chemistry
Keywords: A3. Molecular beam epitaxy, B1. Antimonides, B1. Bismuth compounds, B2. Semiconducting III-V materials, B2. Semiconducting ternary compounds
Source: Scopus
Source-ID: 85063780657

Research output: Contribution to journalArticleScientificpeer-review

Photovoltaic properties of low-bandgap (0.7–0.9 eV) lattice-matched GaInNAsSb solar junctions grown by molecular beam epitaxy on GaAs

We demonstrate single junction GaInNAsSb solar cells with high nitrogen content, i.e. in the range of 5–8%, and bandgap energies close to 0.7 eV grown by molecular beam epitaxy. A good crystalline quality is demonstrated for the entire range of N concentrations. An average external quantum efficiency of 0.45 is demonstrated for GaInNAsSb solar cell with 6.2% N exhibiting a bandgap of 0.78 eV (no antireflection coatings has been applied). The internal quantum efficiency for the cell is 0.65 at E g + 0.2 eV. The solar cells exhibited bandgap-voltage offsets between 0.55 V (for N = 5.3%) and 0.66 V (for N = 7.9%). When used in a six-junction solar cell architecture under AM1.5D illumination, the estimated short-circuit current density corresponding to the 0.78 eV cell is 8.2 mA/cm 2 . Furthermore, using the parameters obtained for the GaInNAsSb junction with 6.2% N, we have estimated that such six-junction solar cell architecture could realistically attain an efficiency of over 50% at 1000 suns concentration.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: ORC, Research group: Nanophotonics, Microscopy Center
Contributors: Isoaho, R., Aho, A., Tukiainen, A., Aho, T., Raappana, M., Salminen, T., Reuna, J., Guina, M.
Number of pages: 6
Pages: 198-203
Publication date: 15 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Solar Energy Materials and Solar Cells
Volume: 195
ISSN (Print): 0927-0248
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Renewable Energy, Sustainability and the Environment, Surfaces, Coatings and Films
Keywords: Dilute nitrides, GaInNAsSb, Molecular beam epitaxy, Multijunction solar cells
Source: Scopus
Source-ID: 85062810786

Research output: Contribution to journalArticleScientificpeer-review

Role of fracture toughness in impact-abrasion wear

Two new low alloyed steels were developed with different fracture toughness values but at similar level of hardness with same composition and microstructural phase. The steels were subjected to impact-abrasion wear test. This work examines specifically the additional role of toughness during impact-abrasion wear, using a newly developed high toughness steel. Microstructural characterisation of the damaged samples revealed that better toughness helps resist both impact and abrasion damage.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, University of Cambridge, Tata Steel Ltd.
Contributors: Chintha, A. R., Valtonen, K., Kuokkala, V. T., Kundu, S., Peet, M. J., Bhadeshia, H. K.
Number of pages: 8
Pages: 430-437
Publication date: 15 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Wear
Volume: 428-429
ISSN (Print): 0043-1648
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Mechanics of Materials, Surfaces and Interfaces, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Abrasion, Fracture toughness, Impact-abrasion, Steel, Wear testing
Electronic versions: 
Source: Scopus
Source-ID: 85064619336

Research output: Contribution to journalArticleScientificpeer-review

Tailoring Second-Harmonic Emission from (111)-GaAs Nanoantennas

Second-harmonic generation (SHG) in resonant dielectric Mie-scattering nanoparticles has been hailed as a powerful platform for nonlinear light sources. While bulk-SHG is suppressed in elemental semiconductors, for example, silicon and germanium due to their centrosymmetry, the group of zincblende III-V compound semiconductors, especially (100)-grown AlGaAs and GaAs, have recently been presented as promising alternatives. However, major obstacles to push the technology toward practical applications are the limited control over directionality of the SH emission and especially zero forward/backward radiation, resulting from the peculiar nature of the second-order nonlinear susceptibility of this otherwise highly promising group of semiconductors. Furthermore, the generated SH signal for (100)-GaAs nanoparticles depends strongly on the polarization of the pump. In this work, we provide both theoretically and experimentally a solution to these problems by presenting the first SHG nanoantennas made from (111)-GaAs embedded in a low index material. These nanoantennas show superior forward directionality compared to their (100)-counterparts. Most importantly, based on the special symmetry of the crystalline structure, it is possible to manipulate the SHG radiation pattern of the nanoantennas by changing the pump polarization without affecting the linear properties and the total nonlinear conversion efficiency, hence paving the way for efficient and flexible nonlinear beam-shaping devices.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Nonlinear Optics, Physics, Australian National University, Friedrich-Schiller-University Jena, School of Engineering and Information Technology, University of New South Wales (UNSW) Australia, Russian Academy of Sciences
Contributors: Sautter, J. D., Xu, L., Miroshnichenko, A. E., Lysevych, M., Volkovskaya, I., Smirnova, D. A., Camacho-Morales, R., Zangeneh Kamali, K., Karouta, F., Vora, K., Tan, H. H., Kauranen, M., Staude, I., Jagadish, C., Neshev, D. N., Rahmani, M.
Number of pages: 7
Pages: 3905-3911
Publication date: 12 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Nano Letters
Volume: 19
Issue number: 6
ISSN (Print): 1530-6984
Original language: English
ASJC Scopus subject areas: Bioengineering, Chemistry(all), Materials Science(all), Condensed Matter Physics, Mechanical Engineering
Keywords: Dielectric nanoantennas, directional emission, III-V semiconductors, Mie resonance, multipolar interference, second harmonic generation
Source: Scopus
Source-ID: 85067057047

Research output: Contribution to journalArticleScientificpeer-review

The Role of Temperature and Lipid Charge on Intake/Uptake of Cationic Gold Nanoparticles into Lipid Bilayers

Understanding the molecular mechanisms governing nanoparticle–membrane interactions is of prime importance for drug delivery and biomedical applications. Neutron reflectometry (NR) experiments are combined with atomistic and coarse-grained molecular dynamics (MD) simulations to study the interaction between cationic gold nanoparticles (AuNPs) and model lipid membranes composed of a mixture of zwitterionic di-stearoyl-phosphatidylcholine (DSPC) and anionic di-stearoyl-phosphatidylglycerol (DSPG). MD simulations show that the interaction between AuNPs and a pure DSPC lipid bilayer is modulated by a free energy barrier. This can be overcome by increasing temperature, which promotes an irreversible AuNP incorporation into the lipid bilayer. NR experiments confirm the encapsulation of the AuNPs within the lipid bilayer at temperatures around 55 °C. In contrast, the AuNP adsorption is weak and impaired by heating for a DSPC–DSPG (3:1) lipid bilayer. These results demonstrate that both the lipid charge and the temperature play pivotal roles in AuNP–membrane interactions. Furthermore, NR experiments indicate that the (negative) DSPG lipids are associated with lipid extraction upon AuNP adsorption, which is confirmed by coarse-grained MD simulations as a lipid-crawling effect driving further AuNP aggregation. Overall, the obtained detailed molecular view of the interaction mechanisms sheds light on AuNP incorporation and membrane destabilization.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Biological Physics and Soft Matter, Research area: Computational Physics, Physics, Computational Physics Laboratory, University of Helsinki, Politecnico di Milano, Institut Laue-Langevin, Max Planck Institute of Colloids and Interfaces, MEMPHYS−Center for Biomembrane Physics, Norwegian Univ. of Sci. and Technol., G2Elab/Institut Néel
Contributors: Lolicato, F., Joly, L., Martinez-Seara, H., Fragneto, G., Scoppola, E., Baldelli Bombelli, F., Vattulainen, I., Akola, J., Maccarini, M.
Publication date: 7 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Small
Volume: 15
Issue number: 23
Article number: 1805046
ISSN (Print): 1613-6810
Original language: English
ASJC Scopus subject areas: Biotechnology, Biomaterials, Chemistry(all), Materials Science(all)
Keywords: gold nanoparticles, lipid membranes, molecular dynamics simulations, nanotoxicity, neutron reflectometry
Electronic versions: 

Bibliographical note

EXT="Martinez-Seara, Hector"

Source: Scopus
Source-ID: 85064688737

Research output: Contribution to journalArticleScientificpeer-review

Analytical Expressions for Spring Constants of Capillary Bridges and Snap-in Forces of Hydrophobic Surfaces

When a force probe with a small liquid drop adhered to its tip makes contact with a substrate of interest, the normal force right after contact is called the snap-in force. This snap-in force is related to the advancing contact angle or the contact radius at the substrate. Measuring snap-in forces has been proposed as an alternative to measure the advancing contact angles of surfaces. The snap-in occurs when the distance between the probe surface and the substrate is hS, which is amenable to geometry, assuming the drop was a spherical cap before snap-in. Equilibrium is reached at a distance hE < hS. At equilibrium, the normal force F = 0, and the capillary bridge is a spherical segment, amenable again to geometry. For a small normal displacement Δh = h - hE, the normal force can be approximated with F ≈ -k1Δh or F ≈ -k1Δh - k2Δh2, where k1 = -∂F/∂h and k2 = -1/2·∂2F/∂h2 are the effective linear and quadratic spring constants of the bridge, respectively. Analytical expressions for k1,2 are found using Kenmotsu's parameterization. Fixed contact angle and fixed contact radius conditions give different forms of k1,2. The expressions for k1 found here are simpler, yet equivalent to the earlier derivation by Kusumaatmaja and Lipowsky (2010). Approximate snap-in forces are obtained by setting Δh = hS - hE. These approximate analytical snap-in forces agree with the experimental data from Liimatainen et al. (2017) and a numerical method based on solving the shape of the interface. In particular, the approximations are most accurate for super liquid-repellent surfaces. For such surfaces, readers may find this new analytical method more convenient than solving the shape of the interface numerically.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech
Contributors: Sariola, V.
Number of pages: 7
Pages: 7129-7135
Publication date: 4 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Langmuir
Volume: 35
Issue number: 22
ISSN (Print): 0743-7463
Original language: English
ASJC Scopus subject areas: Materials Science(all), Condensed Matter Physics, Surfaces and Interfaces, Spectroscopy, Electrochemistry
Electronic versions: 
Source: Scopus
Source-ID: 85066806357

Research output: Contribution to journalArticleScientificpeer-review

Correlation of Surface Morphology and Interfacial Adhesive Behavior between Cellulose Surfaces: Quantitative Measurements in Peak-Force Mode with the Colloidal Probe Technique

A better understanding of cellulose-cellulose interactions is needed in applications such as paper making and all-cellulose composites. To date, cellulose-cellulose studies have been chemistry-oriented. In these studies, the sample surfaces have been modified with different chemicals and then tested under an atomic force microscope (AFM) using a colloidal probe (CP). Studies of cellulose-cellulose interaction based on sample morphology and mechanical properties have been rare as a result of the complex surface structure and the soft texture of the cellulose. The current surface interaction models, such as the Johnson-Kendall-Roberts (JKR) model in which the studied bodies are assumed to have smooth surfaces, can no longer fully reveal the interfacial behavior between two cellulose surfaces. Therefore, we propose a new type of contact model for rough-rough interaction by dividing the surface contacts into primary and secondary levels. The main idea of the new model is to take into account local individual contact details between rough surfaces. The model considers the effect of the surface topography by including the asperities and valleys on a cellulose sphere used as the colloidal probe in imaging the topography of a cellulose membrane (CM). In addition, the correlation between the surface morphology and adhesion is studied. To verify the importance of including the effect of the surface roughness in contact analysis and validate our hypothesis on the correlation between the surface morphology and adhesion, an extensive set of experiments was performed. In the experiments, a combination of the AFM peak-force mode (PFM) and the CP technique was employed to acquire a massive amount of information on cellulose-cellulose interactions by measuring the adhesion among six CSs of different sizes and a CM.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Micro and Nanosystems Research Group, BioMediTech, Harbin Institute of Technology, Tokyo University of Science
Contributors: Lai, Y., Zhang, H., Sugano, Y., Xie, H., Kallio, P.
Number of pages: 10
Pages: 7312-7321
Publication date: 4 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Langmuir
Volume: 35
Issue number: 22
ISSN (Print): 0743-7463
Original language: English
ASJC Scopus subject areas: Materials Science(all), Condensed Matter Physics, Surfaces and Interfaces, Spectroscopy, Electrochemistry
Electronic versions: 
Source: Scopus
Source-ID: 85066731882

Research output: Contribution to journalArticleScientificpeer-review

Bioactive glass ions induce efficient osteogenic differentiation of human adipose stem cells encapsulated in gellan gum and collagen type I hydrogels

Background: Due to unmet need for bone augmentation, our aim was to promote osteogenic differentiation of human adipose stem cells (hASCs) encapsulated in gellan gum (GG) or collagen type I (COL) hydrogels with bioactive glass (experimental glass 2-06 of composition [wt-%]: Na 2 O 12.1, K 2 O 14.0, CaO 19.8, P 2 O5 2.5, B 2 O 3 1.6, SiO 2 50.0) extract based osteogenic medium (BaG OM) for bone construct development. GG hydrogels were crosslinked with spermidine (GG-SPD) or BaG extract (GG-BaG). Methods: Mechanical properties of cell-free GG-SPD, GG-BaG, and COL hydrogels were tested in osteogenic medium (OM) or BaG OM at 0, 14, and 21 d. Hydrogel embedded hASCs were cultured in OM or BaG OM for 3, 14, and 21 d, and analyzed for viability, cell number, osteogenic gene expression, osteocalcin production, and mineralization. Hydroxyapatite-stained GG-SPD samples were imaged with Optical Projection Tomography (OPT) and Selective Plane Illumination Microscopy (SPIM) in OM and BaG OM at 21 d. Furthermore, Raman spectroscopy was used to study the calcium phosphate (CaP) content of hASC-secreted ECM in GG-SPD, GG-BaG, and COL at 21 d in BaG OM. Results: The results showed viable rounded cells in GG whereas hASCs were elongated in COL. Importantly, BaG OM induced significantly higher cell number and higher osteogenic gene expression in COL. In both hydrogels, BaG OM induced strong mineralization confirmed as CaP by Raman spectroscopy and significantly improved mechanical properties. GG-BaG hydrogels rescued hASC mineralization in OM. OPT and SPIM showed homogeneous 3D cell distribution with strong mineralization in BaG OM. Also, strong osteocalcin production was visible in COL. Conclusions: Overall, we showed efficacious osteogenesis of hASCs in 3D hydrogels with BaG OM with potential for bone-like grafts.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Biomaterials and Tissue Engineering Group, BioMediTech, Research group: Computational Biophysics and Imaging Group, Tampere University Hospital, Research, University of Jyvaskyla, Abo Akad Univ, Abo Akademi University, Dept Phys, Tampere University of Applied Sciences
Contributors: Vuornos, K., Ojansivu, M., Koivisto, J. T., Häkkänen, H., Belay, B., Montonen, T., Huhtala, H., Kääriäinen, M., Hupa, L., Kellomäki, M., Hyttinen, J., Ihalainen, J. A., Miettinen, S.
Number of pages: 14
Pages: 905-918
Publication date: 1 Jun 2019
Peer-reviewed: Yes

Publication information

Journal: Materials Science and Engineering C
Volume: 99
ISSN (Print): 0928-4931
Original language: English
ASJC Scopus subject areas: Materials Science(all), Condensed Matter Physics, Mechanics of Materials, Mechanical Engineering
Keywords: Adipose stem cell, Bioactive glass, Collagen type I hydrogel, Gellan gum hydrogel, Osteogenic differentiation

Bibliographical note

DUPL=47148426

Source: Scopus
Source-ID: 85061661719

Research output: Contribution to journalArticleScientificpeer-review

Energy density-method: An approach for a quick estimation of quench temperatures in high-field accelerator magnets

Accelerator magnets for future particle accelerators are designed to work with as high energy densities as possible to achieve high fields and compact magnet designs. A key factor limiting the energy density is given by the protection in case of quench: If a quench occurs, the stored energy must be first absorbed by the windings, and the magnet temperature shall not exceed a given limit. In this paper, we present a back-of-the-envelope method for estimating the magnet&#x0027;s maximum temperature after a quench based on its stored energy. The method combines the existing concepts of MIITs, time margin, and protection delay to allow for easy and direct calculation of the hot-spot temperature. We apply the proposed method to several Nb3Sn dipole and quadrupole magnets developed for HL-LHC (High Luminosity LHC) and the FCC-hh (Future Circular Collider for hadron-hadron collisions) and compare the results to a more detailed simulation. The proposed Energy density-method is a useful tool for fast feedback in the early magnet design phase to ensure that the magnet is not impossible to protect.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, Research area: Power engineering, Research group: Modelling and superconductivity, European Organization for Nuclear Research
Contributors: Salmi, T., Schoerling, D.
Publication date: Jun 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 29
Issue number: 4
ISSN (Print): 1051-8223
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Conductivity, Copper, Energy storage, Heating systems, Magnetic circuits, Superconducting magnets, Temperature
Source: Scopus
Source-ID: 85056300732

Research output: Contribution to journalArticleScientificpeer-review

Simulation of Delamination Growth at CFRP-Tungsten Aerospace Laminates Using VCCT and CZM Modelling Techniques

Delamination analysis in advanced composites is required for the laminate design phase and also during the operation of composite aerospace structures to estimate the criticality of flaws and damage. The virtual crack closure technique (VCCT) and cohesive zone modelling (CZM) have been applied to delamination simulation as numerical tools of crack modelling. VCCT and CZM have their unique advantages and disadvantages per application. This study focuses on the application of VCCT to a brittle delamination in a hybrid tungsten–carbon-fibre reinforced composite (CFRP-W) and pursues to identify the challenges due to very high internal residual stresses and strain energy as well as unstable crack propagation. The CFRP-W composites have application areas in high-performance, light-weight radiation protection enclosures of satellite electronics and ultra-high frequency (e.g. 5G) systems. In our work, we present the effects of free-edge stress concentrations and interfacial separation prior to nodal release on a combined VCCT-CZM model and compare the results to pure VCCT and CZM models of the interfacial crack. Parameter notes are given based on the results to apply the combined method for delamination analyses with interfaces heavily loaded by internal residual strains.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Plastics and Elastomer Technology
Contributors: Jokinen, J., Kanerva, M.
Number of pages: 13
Pages: 709-721
Publication date: Jun 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Applied Composite Materials
Volume: 26
Issue number: 3
ISSN (Print): 0929-189X
Original language: English
ASJC Scopus subject areas: Ceramics and Composites
Keywords: CZM, Delamination, Finite element simulation, Satellite enclosure, VCCT
Source: Scopus
Source-ID: 85056829668

Research output: Contribution to journalArticleScientificpeer-review

Lasing in Ni Nanodisk Arrays

We report on lasing at visible wavelengths in arrays of ferromagnetic Ni nanodisks overlaid with an organic gain medium. We demonstrate that by placing an organic gain material within the mode volume of the plasmonic nanoparticles both the radiative and, in particular, the high ohmic losses of Ni nanodisk resonances can be compensated. Under increasing pump fluence, the systems exhibit a transition from lattice-modified spontaneous emission to lasing, the latter being characterized by highly directional and sub-nanometer line width emission. By breaking the symmetry of the array, we observe tunable multimode lasing at two wavelengths corresponding to the particle periodicity along the two principal directions of the lattice. Our results are relevant for loss-compensated magnetoplasmonic devices and topological photonics.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Aalto University, University of Eastern Finland, Campus de la UAB
Contributors: Pourjamal, S., Hakala, T. K., Nečada, M., Freire-Fernández, F., Kataja, M., Rekola, H., Martikainen, J. P., Törmä, P., Van Dijken, S.
Number of pages: 7
Pages: 5686-5692
Publication date: 28 May 2019
Peer-reviewed: Yes

Publication information

Journal: ACS Nano
Volume: 13
Issue number: 5
ISSN (Print): 1936-0851
Original language: English
ASJC Scopus subject areas: Materials Science(all), Engineering(all), Physics and Astronomy(all)
Keywords: loss-compensated magnetoplasmonics, nanolasing, Ni nanodisk array, plasmonics, surface lattice resonance
Electronic versions: 
Source: Scopus
Source-ID: 85064967811

Research output: Contribution to journalArticleScientificpeer-review

Fabrication of soft devices with buried fluid channels by using sacrificial 3D printed molds

Casting silicone elastomers into 3D printed molds has seen a surge of applications in soft robots, soft manipulators, microfluidics, wearable technologies and stretchable sensors. In such devices, buried fluid channels are used to transport fluids, as fluidic actuators and as sensors with liquid metal. However, it is difficult to demold structures with buried channels or overhangs. As a solution, using sacrificial molds made of dissolvable materials has been proposed. In this paper, we evaluate different commercially available 3D printing materials as dissolvable mold materials. We tested dissolving prints made of high-impact polystyrene (HIPS), acrylonitrile butadiene styrene (ABS), polyvinyl butyral (PVB) and polyvinyl alcohol (PVA) in limonene, acetone, isopropanol/ethanol and water, respectively. We further studied the effect of magnetic stirring and ultrasonic bath on the dissolution times. Finally, we fabricated buried channels using different mold materials and silicone elastomers. The results show that at least ABS, PVB and PVA can be used as mold materials. In particular, PVA is a promising material as it is soluble in water. The studied method simplifies the fabrication of soft devices, allowing the fabrication of overhangs and buried channels in a single casting step.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: BioMediTech
Contributors: Koivikko, A., Sariola, V.
Number of pages: 5
Pages: 509-513
Publication date: 24 May 2019

Host publication information

Title of host publication: 2019 2nd IEEE International Conference on Soft Robotics (RoboSoft)
Publisher: IEEE
ISBN (Electronic): 9781538692608
ASJC Scopus subject areas: Materials Science (miscellaneous), Artificial Intelligence, Mechanical Engineering, Control and Optimization
Source: Scopus
Source-ID: 85067126836

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Multistep Bloch-line-mediated Walker breakdown in ferromagnetic strips

A well-known feature of magnetic field driven dynamics of domain walls in ferromagnets is the existence of a threshold driving force at which the internal magnetization of the domain wall starts to precess - a phenomenon known as the Walker breakdown - resulting in an abrupt drop of the domain-wall propagation velocity. Here, we report on micromagnetic simulations of magnetic field driven domain-wall dynamics in thin ferromagnetic strips with perpendicular magnetic anisotropy which demonstrate that in wide enough strips Walker breakdown is a multistep process: It consists of several distinct velocity drops separated by short linear parts of the velocity vs field curve. These features originate from the repeated nucleation, propagation, and annihilation of an increasing number of Bloch lines within the domain wall as the driving field magnitude is increased. This mechanism arises due to magnetostatic effects breaking the symmetry between the two ends of the domain wall.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Aalto University, COMP Centre of Excellence, Computational Physics Laboratory
Contributors: Hütner, J., Herranen, T., Laurson, L.
Publication date: 24 May 2019
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 99
Issue number: 17
Article number: 174427
ISSN (Print): 2469-9950
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source-ID: 85066395811

Research output: Contribution to journalArticleScientificpeer-review

Reaction between Peroxy and Alkoxy Radicals Can Form Stable Adducts

Peroxy (RO 2 ) and alkoxy (RO) radicals are prototypical intermediates in any hydrocarbon oxidation. In this work, we use computational methods to (1) study the mechanism and kinetics of the RO 2 + OH reaction for previously unexplored "R" structures (R = CH(O)CH 2 and R = CH 3 C(O)) and (2) investigate a hitherto unaccounted channel of molecular growth, R′O 2 + RO. On the singlet surface, these reactions rapidly form ROOOH and R′OOOR adducts, respectively. The former decomposes to RO + HO 2 and R(O)OH + O 2 products, while the main decomposition channel for the latter is back to the reactant radicals. Decomposition rates of R′OOOR adducts varied between 103 and 0.015 s -1 at 298 K and 1 atm. The most long-lived R′OOOR adducts likely account for some fraction of the elemental compositions detected in the atmosphere that are commonly assigned to stable covalently bound dimers.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, University of Helsinki
Contributors: Iyer, S., Rissanen, M. P., Kurtén, T.
Number of pages: 7
Pages: 2051-2057
Publication date: 2 May 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry Letters
Volume: 10
Issue number: 9
ISSN (Print): 1948-7185
Original language: English
ASJC Scopus subject areas: Materials Science(all), Physical and Theoretical Chemistry
Electronic versions: 
Source: Scopus
Source-ID: 85064871304

Research output: Contribution to journalArticleScientificpeer-review

Energy-dependent diffusion in a soft periodic Lorentz gas

The periodic Lorentz gas is a paradigmatic model to examine how macroscopic transport emerges from microscopic chaos. It consists of a triangular lattice of circular hard scatterers with a moving point particle. Recently this system became relevant as a model for electronic transport in low-dimensional nanosystems such as molecular graphene. However, to more realistically mimic such dynamics, the hard Lorentz gas scatterers should be replaced by soft potentials. Here we study diffusion in a soft Lorentz gas with Fermi potentials under variation of the total energy of the moving particle. Our goal is to understand the diffusion coefficient as a function of the energy. In our numerical simulations we identify three different dynamical regimes: (i) the onset of diffusion at small energies; (ii) a transition where for the first time a particle reaches the top of the potential, characterized by the diffusion coefficient abruptly dropping to zero; and (iii) diffusion at high energies, where the diffusion coefficient increases according to a power law in the energy. All these different regimes are understood analytically in terms of simple random walk approximations.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research area: Computational Physics, Research group: Quantum Control and Dynamics, Physics, School of Mathematical Sciences, Technische Universität Berlin, Universitat zu Koln, Computational Physics Laboratory
Contributors: Gil-Gallegos, S., Klages, R., Solanpää, J., Räsänen, E.
Number of pages: 18
Pages: 143-160
Publication date: 1 May 2019
Peer-reviewed: Yes

Publication information

Journal: European Physical Journal: Special Topics
Volume: 228
Issue number: 1
ISSN (Print): 1951-6355
Original language: English
ASJC Scopus subject areas: Materials Science(all), Physics and Astronomy(all), Physical and Theoretical Chemistry
Source: Scopus
Source-ID: 85066258822

Research output: Contribution to journalArticleScientificpeer-review

GaInAsSb/AlGa(In)AsSb type I quantum wells emitting in 3 μm range for application in superluminescent diodes

In this paper, we present results of Fourier-transformed photoluminescence measurements of quaternary GaInAsSb quantum wells with quinary AlGaInAsSb barriers grown on GaSb substrate, designed for spectral range of mid-infrared. Here, we show an emission shift towards longer wavelength as a result of incorporation of indium into the quantum wells reaching up to 3 μm at room temperature (RT). Additionally, we have observed an additional low-energy photoluminescence signal with maximum wavelength of 3.5 μm at RT, which we have attributed as states localised on the layer interfaces. The activation energy of carriers trapped in those states is estimated to be 35 meV.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: ORC, Physics, Wrocław University of Technology
Contributors: Kurka, M., Dyksik, M., Suomalainen, S., Koivusalo, E., Guina, M., Motyka, M.
Number of pages: 5
Pages: 274-278
Publication date: 1 May 2019
Peer-reviewed: Yes

Publication information

Journal: Optical Materials
Volume: 91
ISSN (Print): 0925-3467
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Computer Science(all), Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: Fourier-transformed spectroscopy, MBE, Optical gas sensing, Photoluminescence, Superluminescent diodes
Source: Scopus
Source-ID: 85063381328

Research output: Contribution to journalArticleScientificpeer-review

Surface reactivity and silanization ability of borosilicate and Mg-Sr-based bioactive glasses

Borosilicate bioactive glasses are attracting an increasing interest due to their good hot forming ability, low crystallization tendency and high bioactivity. Surface functionalization of bioactive glasses is a versatile tool for modulation of their properties and consequently of their biological response and it is still an unexplored topic in the case of borosilicate glasses. The possibility to graft 3-aminopropyltriethoxysilane (APTES) to various borosilicate bioactive glasses have been investigated in the present research work. Glasses were produced by melting and completely characterized (SEM-EDS, density, FTIR-ATR, Raman, NMR, zeta potential and reactivity in SBF and TRIS/HCl). Then, APTES was grafted to the surface of the glasses and its presence was verified by means of XPS, contact angle and zeta potential measurements. This study has shown the possibility to silanize borosilicate bioactive glasses for the first time, however, this silanization protocol does not induce the formation of a continuous coating on the glass surface.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Biomaterials and Tissue Engineering Group, Politecnico di Torino
Contributors: Ferraris, S., Nommeots-Nomm, A., Spriano, S., Vernè, E., Massera, J.
Number of pages: 13
Pages: 43-55
Publication date: 1 May 2019
Peer-reviewed: Yes
Early online date: 26 Dec 2018

Publication information

Journal: Applied Surface Science
Volume: 475
ISSN (Print): 0169-4332
Original language: English
ASJC Scopus subject areas: Surfaces, Coatings and Films
Keywords: APTES, Borosilicate bioactive glasses, Silanization
Source: Scopus
Source-ID: 85059228057

Research output: Contribution to journalArticleScientificpeer-review

Moiré superlattices and 2D electronic properties of graphite/MoS2 heterostructures

Heterostructures of graphite/MoS2 display a wide range of lattice registry due to rotational alignment and/or lattice mismatch. Using high resolution scanning tunneling microscopy and spectroscopy (STM/STS) we investigated electronic properties of these heterostructures and observed changes in the bandgap as a function of the twist angle between the layers. Green's function based electronic structure calculations were carried out in order to shed light on the mechanism underlying the observed bandgap changes. Indirect coupling between the pz orbitals of the substrate Carbon atoms and the dz2 orbitals of the MoS2 layers (mediated by the pz orbitals of the bottom S layers) is found to be responsible for changes in the valence-band edge. Simple stacking of van der Waals materials with diverse properties have the potential to enable the fabrication of novel materials and device structures with tailored electronic properties.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Temple University, Russian Academy of Sciences, Northeastern University, National Tsing-Hua University, Institute of Physics Academia Sinica Taiwan, National University of Singapore
Contributors: Trainer, D. J., Putilov, A. V., Wang, B., Lane, C., Saari, T., Chang, T. R., Jeng, H. T., Lin, H., Xi, X., Nieminen, J., Bansil, A., Iavarone, M.
Pages: 325-330
Publication date: May 2019
Peer-reviewed: Yes
Early online date: 2017

Publication information

Journal: Journal of Physics and Chemistry of Solids
Volume: 128
ISSN (Print): 0022-3697
Original language: English
ASJC Scopus subject areas: Chemistry(all), Materials Science(all), Condensed Matter Physics
Source: Scopus
Source-ID: 85036647170

Research output: Contribution to journalArticleScientificpeer-review

Spin filtering in silicene by edges and chemically or electrically induced interfaces

Silicene is a graphene-like material with relatively strong spin-orbit coupling exhibiting gapless topologically protected edge states. In addition, it has a buckled structure, and hence, it stands as a feasible candidate for spintronic applications, where spin-polarized channels could be controlled with external electric fields realized with voltage gates attached to a Silicene sheet. Breaking the periodicity in 2D-materials with spin-orbit coupling produces one-dimensional edge and interface nanostructures that may give rise to an intrinsic locking of spin-polarization to electron momentum. We consider field induced and chemical ways to create interfaces to give way to spin polarized states for both zigzag and armchair alignments. While the spin polarization of a field induced interface channel can be feasibly tuned, a chemical interface is less flexibly tunable. However, controlling Fermi-level, e.g. with a gate voltage, might serve as a spin valve along the interface.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Northeastern University
Contributors: Saari, T., Nieminen, J.
Pages: 316-324
Publication date: May 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Journal of Physics and Chemistry of Solids
Volume: 128
ISSN (Print): 0022-3697
Original language: English
ASJC Scopus subject areas: Chemistry(all), Materials Science(all), Condensed Matter Physics
Keywords: Electronic structure, Green's function techniques, Interfaces, Silicene, Spin-orbit coupling
Source: Scopus
Source-ID: 85040567725

Research output: Contribution to journalArticleScientificpeer-review

Comparison of various high-stress wear conditions and wear performance of martensitic steels

The demanding environments typically encountered by the wear resistant steels create challenges for the materials selection, because the hardness grades of the steels alone do not reveal the true nature of their wear behavior. In this study, five commercial wear resistant steels were tested using three application oriented test methods with five different test variables for abrasion, impact-abrasion, and slurry erosion. All the used test methods produced high-stress conditions that crushed the used mineral abrasive, plastically deformed the sample surfaces, and led to the formation of adiabatic shear bands. When the results produced by the chosen methods were compared, the normalization of the wear losses by the wear area and test time revealed well the differences between the methods. The test methods ranked the steels similarly, but there were clear differences in the wear rates and wear mechanisms between the tests. In addition, the abrasive methods produced surface adiabatic shear bands, while subsurface shear bands were initiated by the more impacting methods. In the studied conditions, the work hardening ability of the steel had a clear influence on its wear resistance, which largely explains the marked differences in the wear rates of the studied commercial 500HB grade steels.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Materials Characterization, Materials Science and Environmental Engineering, Robit Ltd, Univ of Oulu
Contributors: Valtonen, K., Ojala, N., Haiko, O., Kuokkala, V.
Number of pages: 11
Pages: 3-13
Publication date: 30 Apr 2019
Peer-reviewed: Yes

Publication information

Journal: Wear
Volume: 426-427
Issue number: Part A
ISSN (Print): 0043-1648
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Mechanics of Materials, Materials Chemistry, Surfaces, Coatings and Films, Surfaces and Interfaces
Keywords: Abrasion, Impact wear, Steel, Wear testing, ABRASIVE WEAR, BEHAVIOR, FIELD, RESISTANT STEELS, COMPRESSION, MICROSTRUCTURE
Source: Scopus
Source-ID: 85058455176

Research output: Contribution to journalArticleScientificpeer-review

Complex Behavior of Phosphatidylcholine-Phosphatidic Acid Bilayers and Monolayers: Effect of Acyl Chain Unsaturation

Phosphatidic acids (PAs) have many biological functions in biomembranes, e.g., they are involved in the proliferation, differentiation, and transformation of cells. Despite decades of research, the molecular understanding of how PAs affect the properties of biomembranes remains elusive. In this study, we explored the properties of lipid bilayers and monolayers composed of PAs and phosphatidylcholines (PCs) with various acyl chains. For this purpose, the Langmuir monolayer technique and atomistic molecular dynamics (MD) simulations were used to study the miscibility of PA and PC lipids and the molecular organization of mixed bilayers. The monolayer experiments demonstrated that the miscibility of membrane components strongly depends on the structure of the hydrocarbon chains and thus on the overall lipid shape. Interactions between PA and PC molecules vary from repulsive, for systems containing lipids with saturated and unsaturated acyl tails (strongly positive values of the excess free energy of mixing), to attractive, for systems in which all lipid tails are saturated (negative values of the excess free energy of mixing). The MD simulations provided atomistic insight into polar interactions (formation of hydrogen bonds and charge pairs) in PC-PA systems. H-bonding between PA monoanions and PCs in mixed bilayers is infrequent, and the lipid molecules interact mainly via electrostatic interactions. However, the number of charge pairs significantly decreases with the number of unsaturated lipid chains in the PA-PC system. The PA dianions weakly interact with the zwitterionic lipids, but their headgroups are more hydrated as compared to the monoanionic form. The acyl chains in all PC-PA bilayers are more ordered compared to single-component PC systems. In addition, depending on the combination of lipids, we observed a deeper location of the PA phosphate groups compared to the PC phosphate groups, which can alter the presentation of PAs for the peripheral membrane proteins, affecting their accessibility for binding. ©

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Biological Physics and Soft Matter, Research area: Computational Physics, University of Helsinki, Uniwersytet Jagiellonski w Krakowie
Contributors: Kulig, W., Korolainen, H., Zatorska, M., Kwolek, U., Wydro, P., Kepczynski, M., Róg, T.
Number of pages: 13
Pages: 5944-5956
Publication date: 30 Apr 2019
Peer-reviewed: Yes

Publication information

Journal: Langmuir
Volume: 35
Issue number: 17
ISSN (Print): 0743-7463
Original language: English
ASJC Scopus subject areas: Materials Science(all), Condensed Matter Physics, Surfaces and Interfaces, Spectroscopy, Electrochemistry
Source: Scopus
Source-ID: 85065022226

Research output: Contribution to journalArticleScientificpeer-review

Engineering of Chern insulators and circuits of topological edge states

Impurities embedded in electronic systems induce bound states which under certain circumstances can hybridize and lead to impurity bands. Doping of insulators with impurities has been identified as a promising route toward engineering electronic topological states of matter. In this paper we show how to realize tuneable Chern insulators starting from a three-dimensional topological insulator whose surface is gapped and intentionally doped with magnetic impurities. The main advantage of the protocol is that it is robust and in particular not very sensitive to the impurity configuration. We explicitly demonstrate this for a square lattice of impurities as well as a random lattice. In both cases we show that it is possible to change the Chern number of the system by one through manipulating its topological state. We also discuss how this can be used to engineer circuits of edge channels.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, University College Dublin, Ireland, Christina Thorpe, Utrecht University, Aalto University, COMP Centre of Excellence
Contributors: Minarelli, E. L., Poÿhönen, K., Van Dalum, G. A., Ojanen, T., Fritz, L.
Publication date: 10 Apr 2019
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 99
Issue number: 16
Article number: 165413
ISSN (Print): 2469-9950
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source-ID: 85065257719

Research output: Contribution to journalArticleScientificpeer-review

Analysis of GaAsBi growth regimes in high resolution with respect to As/Ga ratio using stationary MBE growth

The control of Bi incorporation and material properties in III-V-Bi alloys has proved challenging due to their high sensitivity to the epitaxial growth parameters. Here, we present a methodology for determining the variation in the Ga, As, and Bi fluxes and the temperature across a stationary substrate in molecular beam epitaxy. By correlating the flux distributions with material properties, we identify distinct regimes for epitaxy of GaAsBi. In particular, we devise a detailed image of the interplay between Bi incorporation and structural properties of a bulk GaAs 0.96 Bi 0.04 layer grown on GaAs(1 0 0) with respect to the As/Ga ratio. The influence of As/Ga is analyzed with high resolution over the important stoichiometric range (i.e. As/Ga = 0.6–1.6). Growth outside the near-stoichiometric As/Ga regime leads to decreased Bi incorporation, decreased structural quality and the formation of Ga, Ga/Bi or Bi droplets. On the other hand, growth at As/Ga = 1.00–1.17 leads to maximized material quality. For this regime, the surface roughness is further optimized by fine-tuning the As/Ga ratio to suppress surface mounding to a value of 0.5 nm. The results reveal the extreme sensitivity of GaAsBi growth to small variations in the As/Ga ratio, and demonstrate the applicability of stationary growth in studying these effects.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: ORC
Contributors: Puustinen, J., Hilska, J., Guina, M.
Number of pages: 9
Pages: 33-41
Publication date: 1 Apr 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Crystal Growth
Volume: 511
ISSN (Print): 0022-0248
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Inorganic Chemistry, Materials Chemistry
Keywords: A3. Molecular beam epitaxy, B1. Bismuth compounds, B2. Semiconducting III-V materials, B2. Semiconducting ternary compounds
Source: Scopus
Source-ID: 85060893423

Research output: Contribution to journalArticleScientificpeer-review

Hydrolysis and drug release from poly(ethylene glycol)-modified lactone polymers with open porosity

The ability to release active agents from a porous scaffold structure in situ enables the simultaneous structural support for the cells proliferating and differentiating towards tissue as well as the stimulation of tissue regeneration. Due to the great potentiality of such approach, drug-releasing scaffolds were fabricated from hydrolytically degradable polymers. Three copolymers of poly(ethylene glycol), ɛ-caprolactone, L- and D,L-lactide were synthesized and blended with bone-growth inducing active agents, dexamethasone (DM) and 2-phospho-L-ascorbic acid trisodium salt (AS). Porous scaffolds were prepared by means of super-critical carbon dioxide foaming. In the final scaffold structures, the particle size, location and the water solubility of the drug affected the release kinetics. As the large and water soluble AS particles were more exposed to the buffer solution compared to small DM particles, the AS release was burst-like whereas DM showed a long-term release. The material structure had a significant effect on the release kinetics as the porous scaffolds released active agents faster compared to the solid cylinders. Furthermore, this study showed the strong effect of polymer degradation and wettability on the release, which were more determinative than the pore architecture.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Aalto University, Orton Orthopaedic Hospital
Contributors: Asikainen, S., Paakinaho, K., Kyhkynen, A. K., Hannula, M., Malin, M., Ahola, N., Kellomäki, M., Seppälä, J.
Number of pages: 11
Pages: 165-175
Publication date: 1 Apr 2019
Peer-reviewed: Yes

Publication information

Journal: European Polymer Journal
Volume: 113
ISSN (Print): 0014-3057
Original language: English
ASJC Scopus subject areas: Physics and Astronomy(all), Organic Chemistry, Polymers and Plastics, Materials Chemistry
Keywords: 2-Phospho-L-ascorbic acid trisodium salt, Bulk degradation, Dexamethasone, Drug release, Hydrolytic degradation, Supercritical carbon dioxide foaming
Source: Scopus
Source-ID: 85060767586

Research output: Contribution to journalArticleScientificpeer-review

Vibration-based delamination detection in curved composite plates

Delamination is one of common damages in fibre-reinforced composite laminates. It is known to cause changes in the vibration characteristics of the laminates, which allows for the use of vibration-based indicators for assessing structural health conditions and identifying potential risk of catastrophic failures. This paper presents a vibration-based approach to assess delamination in fibre reinforced composite curved plates through frequency shifts as indicative parameters. Two algorithms based on computational intelligence, namely artificial neural network (ANN) and surrogate assisted genetic algorithm (SAGA), were employed as inverse algorithms for predicting the location, size and interface of the delamination. The validation of the two algorithms is realized numerically through finite element (FE) studies conducted using a structured selection of parameters of genetic algorithms, number of frequency shifts and database size. Experimental modal testing was conducted using scanning laser vibrometer on five carbon fibre reinforced polymer (CFRP) curved plates. Among these, one was intact and the other four were manufactured with artificially induced laminations. It was confirmed that the two inverse algorithms were able to reasonably predict delamination parameters in curved composite plates. Among the two, SAGA's performance was observed to be better. A sensitivity analysis was further conducted by adding artificial noise to the numerical data to simulate measurement errors for investigating the influence of noise on the accuracy of the two algorithms.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Materials Characterization, Materials Science and Environmental Engineering, Guangzhou University, University of New South Wales (UNSW) Australia
Contributors: Zhang, Z., Pan, J., Luo, W., Ramakrishnan, K. R., Singh, H. K.
Number of pages: 14
Pages: 261-274
Publication date: 1 Apr 2019
Peer-reviewed: Yes

Publication information

Journal: Composites Part A: Applied Science and Manufacturing
Volume: 119
ISSN (Print): 1359-835X
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Mechanics of Materials
Keywords: Artificial neural network, Curved plate, Delamination detection, Genetic algorithm, Natural frequency, Structural health monitoring, Surrogate model
Source: Scopus
Source-ID: 85061304366

Research output: Contribution to journalArticleScientificpeer-review

Ternary borosilicates as potential cladding glasses for semiconductor core optical fibers

Our study advances the development of new ternary silicate glasses for use as a designed cladding for semiconductor core optical fibers using molten core draw process. In order to fabricate high-quality hybrid fibers (homogeneous core shape, low amount of bubbles, low internal stress, no cracking), oxide glasses are the best choice as cladding materials. These glasses should be engineered with tailored thermal properties (coefficient of thermal expansion (CTE) and drawing temperature) so they match those of the semiconductor. Glasses in the system (50SiO2-(20 − x)Na2O-(25 + x)B2O3-5MO) with x = 0 and 10 and MO = ZnO, TiO2, GeO2, Ga2O3, and Al2O3 and in the system 50SiO2-10Na2O-(40 − y)B2O3-yTiO2 with y = 0, 1.25, 2.5, and 5 were investigated. Their thermal properties were measured and discussed with regard to the glass structure analyzed using FTIR spectroscopy. Due to their rigid network, which leads to beneficial thermal properties including low CTE (~5 ppm K−1), the Ge-containing glass with x = 10 is a promising cladding candidate when preparing a Ge core fiber and the Ga or Zn- containing glasses when preparing an InAs core.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Photonics Glasses, Politecnico di Torino
Contributors: Dmitrieva, I., Lopez-Iscoa, P., Milanese, D., Petit, L.
Number of pages: 6
Pages: 151-156
Publication date: Apr 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: International Journal of Applied Glass Science
Volume: 10
Issue number: 2
ISSN (Print): 2041-1286
Original language: English
ASJC Scopus subject areas: Materials Science(all)

Bibliographical note

INT=fot,"Dmitrieva, Iuliia"

Source: Scopus
Source-ID: 85054029936

Research output: Contribution to journalArticleScientificpeer-review

Antibacterial activity of silver and titania nanoparticles on glass surfaces

A liquid flame spray (LFS) nanoparticle deposition process was used to generate glass surfaces with silver (Ag) and titania (TiO2) nanoparticles for antibacterial activity against two common pathogenic bacteria causing community-associated and hospital-acquired infections, gram positive Staphylococcus aureus (S aureus) and gram negative Escherichia coli (E coli). All nanoparticle coatings increased antibacterial activity compared to a reference glass surface. The Ag nanoparticle coatings showed the highest antibacterial activity with E coli. On the contrary, TiO2 nanoparticle coatings were found to have a higher antibacterial activity against S aureus than E coli. No significant differences in antibacterial activity were observed between the two used nanoparticle deposition amounts.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Aerosol Synthesis, Research area: Aerosol Physics, Physics, Abo Akad Univ, Abo Akademi University, Dept Phys, University of Turku, Turku University Hospital, University of Eastern Finland
Contributors: Kummala, R., Brobbey, K. J., Haapanen, J., Mäkelä, J. M., Gunell, M., Eerola, E., Huovinen, P., Toivakka, M., Saarinen, J. J.
Publication date: 20 Mar 2019
Peer-reviewed: Yes

Publication information

Journal: ADVANCES IN NATURAL SCIENCES: NANOSCIENCE AND NANOTECHNOLOGY
Volume: 10
Issue number: 1
Article number: 015012
ISSN (Print): 2043-6254
Original language: English
ASJC Scopus subject areas: Materials Science(all), Industrial and Manufacturing Engineering, Electrical and Electronic Engineering
Keywords: antibacterial, E coli, glass, nanoparticle, S aureus
Source: Scopus
Source-ID: 85067126373

Research output: Contribution to journalArticleScientificpeer-review

Advancements in Solution Processable Devices using Metal Oxides For Printed Internet-of-Things Objects

Internet-of-things (IoT) objects are expected to exceed 75 billion objects by 2020, and a large part of the expansion is expected to be at a finer granularity than existing silicon-based IoT objects (i.e. tablets and cell phones) can deliver [1]. Currently, placing a room light or a thermostat on the internet for remote control is considered progressive. However, if printed electronics can achieve performance increases, then IoT objects could be affixed to almost anything, such as coffee creamer cartons, cereal boxes, or that missing sock. Each of these IoT objects could be driving a sensor, perhaps position, temperature or pressure, essentially a multitude of applications. In order for IoT objects to emulate a simple postage stamp, with self-powering from energy scavenging and local energy storage, all housed in a non-toxic flexible form factor, advances in solution processable devices need to occur.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Electrical Engineering, Ohio State University, Wayne State University
Contributors: Berger, P. R., Li, M., Mattei, R. M., Niang, M. A., Talisa, N., Tripepi, M., Harris, B., Bhalerao, S. R., Chowdhury, E. A., Winter, C. H., Lupo, D.
Number of pages: 3
Pages: 160-162
Publication date: 1 Mar 2019

Host publication information

Title of host publication: 2019 Electron Devices Technology and Manufacturing Conference, EDTM 2019
Publisher: IEEE
ISBN (Electronic): 9781538665084
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials, Instrumentation, Hardware and Architecture
Keywords: ALD, CMOS and SOI, energy scavenging, IoT, low-power electronics, Manufacturing, NDR, tunnel diodes
Source: Scopus
Source-ID: 85067814337

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Emission measurements with gravimetric impactors and electrical devices: An aerosol instrument comparison

Particulate matter in the atmosphere is known to affect Earth’s climate and to be harmful to human health. Accurately measuring particles from emission sources is important, as the results are used to inform policies and climate models. This study compares the results of two ELPI + devices, two PM10 cascade impactors and an eFilter, in combustion emission measurements. The comparison of the instruments in a realistic setting shows what types of challenges arise from measuring an emission aerosol with unknown particle morphologies and densities, different particle concentrations and high temperature. Our results show that the PM10 cascade impactors have very good intercorrelation when the collected mass is greater than 150 µg, but below that, the uncertainty of the results increases with decreasing mass. The raw signals of two ELPI + devices were nearly identical in most samples, as well as the particle number concentrations and size distributions calculated from raw signals; however, transforming the current distributions into mass distributions showed variation in the mass concentration of particles larger than 1 µm. The real-time time signal measured by eFilter was similar to the total current measured by ELPI+. The eFilter and PM10 cascade impactors showed similar particle mass concentrations, whereas ELPI + showed clearly higher ones in most cases. We concluded that the difference is at least partially due to volatile components being measured by ELPI+, but not by the mass collection measurements.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: The Instrumentation, Emissions, and Atmospheric Aerosols Group, Research area: Aerosol Physics, Estonian Environmental Research Centre, Dekati Ltd, Tallinn University of Technology, Finnish Meteorological Institute
Contributors: Salo, L., Mylläri, F., Maasikmets, M., Niemelä, V., Konist, A., Vainumäe, K., Kupri, H. L., Titova, R., Simonen, P., Aurela, M., Bloss, M., Keskinen, J., Timonen, H., Rönkkö, T.
Number of pages: 14
Pages: 526-539
Publication date: 1 Mar 2019
Peer-reviewed: Yes

Publication information

Journal: Aerosol Science and Technology
Volume: 53
Issue number: 5
ISSN (Print): 0278-6826
Original language: English
ASJC Scopus subject areas: Environmental Chemistry, Materials Science(all), Pollution
Source: Scopus
Source-ID: 85062494308

Research output: Contribution to journalArticleScientificpeer-review

Stable and unstable friction in fretting contacts

Designing contacts susceptible to fretting is a challenging task due to uncertainties related to friction. For example, coefficient of friction has shown to vary as a function of load cycles and so-called non-Coulomb friction can exist during individual load cycles. Concepts of stable and unstable friction are presented in this manuscript. Based on experiments, no fretting is to be expected if the utilization of friction is kept below unstable friction threshold. If contact is subjected to tangential load above this threshold, reciprocating slippage, fretting, is to be expected even if the contact was initially in stick. Experimental evidence for existence of such threshold is presented in form of friction data, slip data and fretting scars.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Tribology and Machine Elements, Materials Science, Wärtsilä, Univ of Oulu
Contributors: Hintikka, J., Mäntylä, A., Vaara, J., Frondelius, T., Lehtovaara, A.
Number of pages: 10
Pages: 73-82
Publication date: 1 Mar 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Tribology International
Volume: 131
ISSN (Print): 0301-679X
Original language: English
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Surfaces and Interfaces, Surfaces, Coatings and Films
Keywords: Fretting, Friction, Stick-slip, Wear
Source: Scopus
Source-ID: 85055737240

Research output: Contribution to journalArticleScientificpeer-review

The formation and characterization of fretting-induced degradation layers using quenched and tempered steel

Fretting movement is dangerous for machines, because it can cause cracking and surface degradation. The aim of this work was to characterize fretting-induced material degradation in large flat-on-flat contacts without edge effects in a sliding direction using quenched and tempered steel 34CrNiMo6. The focus was on the adhesive contact spots, which were formed under a wide variety of operating conditions. Characterization methods were optical microscopy, Vickers hardness tests and scanning electron microscopy. Three different degradation areas were observed: a general deformation layer, a tribologically transformed structure and a third body layer. All the degradation phases have high hardness and low ductility compared to the base material. The formation and behavior of the degradation layers in different operating conditions were discussed.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Tribology and Machine Elements, Research group: Materials Characterization, Wärtsilä
Contributors: Nurmi, V., Hintikka, J., Juoksukangas, J., Honkanen, M., Vippola, M., Lehtovaara, A., Mäntylä, A., Vaara, J., Frondelius, T.
Number of pages: 10
Pages: 258-267
Publication date: 1 Mar 2019
Peer-reviewed: Yes
Early online date: 14 Sep 2018

Publication information

Journal: Tribology International
Volume: 131
ISSN (Print): 0301-679X
Original language: English
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Surfaces and Interfaces, Surfaces, Coatings and Films
Keywords: Adhesion, Fretting, Friction, Microscopy
Electronic versions: 

Bibliographical note

INT=mol,"Nurmi, Verner"
EXT="Hintikka, Jouko"

Source: Scopus
Source-ID: 85056207084

Research output: Contribution to journalArticleScientificpeer-review

Transverse deformation of a lamellar TiAl alloy at high temperature by in situ microcompression

The distribution of strain in hard mode oriented lamellar stacks of the two-phase γ-TiAl/α2-Ti3Al alloy Ti-45Al-2Nb-2Mn (at.%)-0.8 vol% TiB2 was measured at several temperatures up to 633 °C by in situ micropillar compression, complemented by electron backscatter diffraction orientation mapping and digital image correlation strain mapping of a thermally stable surface Pt speckle pattern. Post-mortem transmission electron microscopy further identified the finest scale deformation structures. It was found that slip and twinning transverse to the lamellae operates within discreet bands that zigzag across the lamellar structure. The shear strain within each band is approximately constant across the pillar width. This is inconsistent with current energetic models for transverse twin formation in γ-TiAl, which assume independent, non-interacting twins. This is explained using a mathematical formulation for the stress required to operate this transverse mechanical twinning as a function of strain. This study has elucidated how the multi-scale combination of several transverse twinning systems on different {111} planes in γ-TiAl lamellae can relieve the elastic stresses generated at a lamellar interface by the primary (highest Schmid factor) twinning system. It is thought that the facilitation of this mechanism will promote the ductilisation of lamellar γ-TiAl alloys. This is crucial for an increased damage tolerance and ease of component manufacture, leading to a more widespread use of γ-TiAl alloys.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, University of Cambridge, Swiss Federal Laboratories for Materials Science and Technology
Contributors: Edwards, T. E. J., Di Gioacchino, F., Goodfellow, A. J., Mohanty, G., Wehrs, J., Michler, J., Clegg, W. J.
Number of pages: 15
Pages: 85-99
Publication date: 1 Mar 2019
Peer-reviewed: Yes
Early online date: 27 Nov 2018

Publication information

Journal: Acta Materialia
Volume: 166
ISSN (Print): 1359-6454
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Polymers and Plastics, Metals and Alloys
Keywords: Deformation twinning, Digital image correlation, Electron backscattering diffraction (EBSD), Scanning transmission electron microscopy, Titanium aluminide polysynthetically twinned crystal (PST)
Source: Scopus
Source-ID: 85058779138

Research output: Contribution to journalArticleScientificpeer-review

Mining tailings as raw materials for reaction-sintered aluminosilicate ceramics: Effect of mineralogical composition on microstructure and properties

This paper presents studies on the utilization of aluminosilicate-based mining tailings as raw materials for mullite-based ceramics. Based on the 3:2 stoichiometric composition, mullite was synthesised by reactive sintering with a series of powder mixtures with alumina additions. X-ray diffractometry and scanning electron microscopy analyses revealed that, at the specific mineralogical composition, mullite structure formed surrounded by an amorphous glass phase in reaction-sintered powder mixtures. Results demonstrated that the chemical and mineralogical composition of mining tailings do have an effect on mullite formation possibilities and, only with the particular mineralogical composition, the mullite formation is possible regardless of the correct Al:Si ratio in tailings. Physical and mechanical properties of the formed ceramics were defined, showing comparable values to 3:2 mullite reference. Mullite structure formation enables a better thermal resistance up to above 1450 °C of the formed tailings-based ceramics compared to other aluminosilicates, reflecting their utilization potential for refractory ceramic applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Materials Characterization, VTT Technical Research Centre of Finland, Geologian tutkimuskeskus
Contributors: Karhu, M., Lagerbom, J., Solismaa, S., Honkanen, M., Ismailov, A., Räisänen, M. L., Huttunen-Saarivirta, E., Levänen, E., Kivikytö-Reponen, P.
Pages: 4840-4848
Publication date: Mar 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Ceramics International
Volume: 45
Issue number: 4
ISSN (Print): 0272-8842
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Process Chemistry and Technology, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Mining tailings, Mullite, Reaction sintering, Refractory ceramics, Utilization

Bibliographical note

EXT="Lagerbom, Juha"

Source: Scopus
Source-ID: 85057276435

Research output: Contribution to journalArticleScientificpeer-review

DLC-treated aramid-fibre composites: Tailoring nanoscale-coating for macroscale performance

This work aims to quantify the effect of a diamond-like carbon coating (DLC) treatment of aramid fibres and to reveal the conversion of a fibre-level performance leap on the macroscale mechanical behaviour. The DLC-based coating is applied directly to the reinforcement and laminates are infused with an epoxy matrix. After characterisation of the coated surfaces, the performance of the composite is analysed via interlaminar shear testing, fatigue testing and damage tolerance testing, microbond tests, and 3D finite element simulation using a cohesive zone model of the interface. The results show that the coating treatment improves the fatigue life and the S-N curve slope for the laminates, while the residual strength after impact damage and environmental conditioning (water immersion at 60 °C) remains high. The scaling factor to convert the performance on macroscale was determined to be 0.17–0.39 for the DLC-based fibre treatment.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Faculty of Natural Sciences, Photonics, Aalto University, DIARC-Technology Oy
Contributors: Kanerva, M., Korkiakoski, S., Lahtonen, K., Jokinen, J., Sarlin, E., Palola, S., Iyer, A., Laurikainen, P., Liu, X. W., Raappana, M., Tervakangas, S., Valden, M.
Number of pages: 8
Pages: 62-69
Publication date: 8 Feb 2019
Peer-reviewed: Yes
Early online date: 30 Nov 2018

Publication information

Journal: Composites Science and Technology
Volume: 171
ISSN (Print): 0266-3538
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Engineering(all)
Keywords: Aramid fibre, Damage tolerance, Finite element analysis (FEA), Interfacial strength, Photoelectron spectroscopy (XPS)
Electronic versions: 
Source: Scopus
Source-ID: 85058435801

Research output: Contribution to journalArticleScientificpeer-review

Initial axial stiffness of welded RHS T joints

Recently, CIDECT (International Committee for the Development and Study of Tubular Structures) has proposed the component method as a unified approach for the design of many types of connections, including welded tubular joints. Although CIDECT provides clear and simple equations for the resistance of welded tubular joints, the design of initial stiffness remains complicated and includes a number of uncertainties. This paper analyzes the theoretical approach for the initial axial stiffness of rectangular hollow section T joints. The validation against experimental data has shown that the component method considerably overestimates the stiffness of T joints. The paper develops new equations for the stiffness of the components “chord face in bending” and “chord side walls in compression”. The equations are based on simplified mechanical models, employing finite element analyses to calculate the parameters for which analytical solutions are found extremely complicated. In addition, the article numerically investigates the effect of chord axial stresses on the axial stiffness of joints and proposes a corresponding chord stress function.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Civil Engineering, Research group: Metal and Light-wight structures, St. Petersburg State Polytechnical University, Technische Universitat Munchen
Contributors: Garifullin, M., Bronzova, M., Pajunen, S., Mela, K., Heinisuo, M.
Number of pages: 14
Pages: 459-472
Publication date: 1 Feb 2019
Peer-reviewed: Yes
Early online date: 11 Nov 2018

Publication information

Journal: Journal of Constructional Steel Research
Volume: 153
ISSN (Print): 0143-974X
Original language: English
ASJC Scopus subject areas: Civil and Structural Engineering, Building and Construction, Mechanics of Materials, Metals and Alloys
Keywords: Axial stiffness, Component method, Initial stiffness, Rectangular hollow section, Tubular joint
Source: Scopus
Source-ID: 85056210825

Research output: Contribution to journalArticleScientificpeer-review

Conductive cellulose based foam formed 3D shapes—from innovation to designed prototype

In this article, we introduce for the first time, a method to manufacture cellulose based electrically conductive non-woven three-dimensional (3D) structures using the foam forming technology. The manufacturing is carried out using a minimum amount of processing steps, materials, and hazardous chemicals. The optimized solution applies a single surfactant type and a single predefined portion for the two main processing steps: (1) the dispersing of nanocellulose (NC) and carbon nanotubes (CNT) and (2) the foam forming process. The final material system has a concentration of the used surfactant that is not only sufficient to form a stable and homogeneous nanoparticle dispersion, but it also results in stable foam in foam forming. In this way, the advantages of the foam forming process can be maximized for this application. The cellulose based composite material has a highly even distribution of CNTs over the NC network, resulting a conductivity level of 7.7 S/m, which increased to the value 8.0 S/m after surfactant removal by acetone washing. Also, the applicability and a design product case 'Salmiakki' were studied where the advantages of the material system were validated for a heating element application.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Automation Technology and Mechanical Engineering, Research group: Plastics and Elastomer Technology, Research and Innovation Services, BioMediTech, Research group: Nanoscale Phenomena and Measurements (NPM), Research group: Sensor Technology and Biomeasurements (STB), Materials Science and Environmental Engineering, Aalto University, VTT Technical Research Centre of Finland
Contributors: Siljander, S., Keinänen, P., Ivanova, A., Lehmonen, J., Tuukkanen, S., Kanerva, M., Björkqvist, T.
Number of pages: 12
Publication date: 31 Jan 2019
Peer-reviewed: Yes

Publication information

Journal: Materials
Volume: 12
Issue number: 3
Article number: 430
ISSN (Print): 1996-1944
Original language: English
ASJC Scopus subject areas: Materials Science(all)
Keywords: Carbon nanotube, Conductivity, Foam forming, Nanocellulose, Salmiakki
Source: Scopus
Source-ID: 85060971565

Research output: Contribution to journalArticleScientificpeer-review

Ultrahigh-pressure form of Si O2 glass with dense pyrite-type crystalline homology

High-pressure synthesis of denser glass has been a longstanding interest in condensed-matter physics and materials science because of its potentially broad industrial application. Nevertheless, understanding its nature under extreme pressures has yet to be clarified due to experimental and theoretical challenges. Here we reveal the formation of OSi4 tetraclusters associated with that of SiO7 polyhedra in SiO2 glass under ultrahigh pressures to 200 gigapascal confirmed both experimentally and theoretically. Persistent homology analyses with molecular dynamics simulations found increased packing fraction of atoms whose topological diagram at ultrahigh pressures is similar to a pyrite-type crystalline phase, although the formation of tetraclusters is prohibited in the crystalline phase. This critical difference would be caused by the potential structural tolerance in the glass for distortion of oxygen clusters. Furthermore, an expanded electronic band gap demonstrates that chemical bonds survive at ultrahigh pressure. This opens up the synthesis of topologically disordered dense oxide glasses.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research area: Computational Physics, Research group: Materials and Molecular Modeling, HCI e 486.1, Tohoku University, National Institute for Materials Science (NIMS), Japan Synchrotron Radiation Research Institute, Japan Advanced Institute of Science and Technology, Japan Science and Technology Agency, Tokyo University of Science, Norwegian Univ. of Sci. and Technol., University of Tokyo, Waseda University, National Institute of Advanced Industrial Science and Technology, Research and Services Division of Materials Data and Integrated System (MaDIS) NIMS, Kyoto Women's University, RIKEN Center for Integrative Medical Sciences, Aalto University, COMP Centre of Excellence, Department of Applied Physics, Aalto University, Division of Electrical Engineering and Computer Science, Kanazawa University
Contributors: Murakami, M., Kohara, S., Kitamura, N., Akola, J., Inoue, H., Hirata, A., Hiraoka, Y., Onodera, Y., Obayashi, I., Kalikka, J., Hirao, N., Musso, T., Foster, A. S., Idemoto, Y., Sakata, O., Ohishi, Y.
Publication date: 29 Jan 2019
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 99
Issue number: 4
Article number: 045153
ISSN (Print): 2469-9950
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics

Bibliographical note

EXT="Foster, A. S."

Source: Scopus
Source-ID: 85060951368

Research output: Contribution to journalArticleScientificpeer-review

Deformation of lamellar γ-TiAl below the general yield stress

The occurrence of plasticity below the macroscopic yield stress during tensile monotonic loading of nearly lamellar Ti-45Al-2Nb-2Mn(at%)-0.8 vol% TiB2 at both 25 °C and 700 °C, and in two conditions of lamellar thickness, was measured by digital image correlation strain mapping of a remodelled Au surface speckle pattern. Such initial plasticity, not necessarily related to the presence of common stress concentrators such as hard particles or cracks, could occur at applied stresses as low as 64% of the general yield stress. For a same applied strain it was more prominent at room temperature, and located as slip and twinning parallel to, and near to or at (respect.) lamellar interfaces of all types in soft mode-oriented colonies. These stretched the full colony width and the shear strain was most intense in the centre of the colonies. Further, the most highly operative microbands of plasticity at specimen fracture were not those most active prior to yielding. The strain mapping results from polycrystalline tensile loading were further compared to those from microcompression testing of soft-mode stacks of lamellae milled from single colonies performed at the same temperatures. Combined with post-mortem transmission electron microscopy of the pillars, the initial plasticity by longitudinal dislocation glide was found to locate within 30–50 nm of the lamellar interfaces, and not at the interfaces themselves. The highly localised plasticity that precedes high cycle fatigue failure is therefore inherently related to the lamellar structure, which predetermines the locations of plastic strain accumulation, even in a single loading cycle.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Materials Characterization, University of Cambridge, Swiss Federal Laboratories for Materials Science and Technology
Contributors: Edwards, T. E. J., Di Gioacchino, F., Goodfellow, A. J., Mohanty, G., Wehrs, J., Michler, J., Clegg, W. J.
Number of pages: 18
Pages: 122-139
Publication date: 15 Jan 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Acta Materialia
Volume: 163
ISSN (Print): 1359-6454
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Polymers and Plastics, Metals and Alloys
Keywords: Deformation twinning, Digital image correlation, Electron backscattering diffraction (EBSD), Pre-yield plasticity, Titanium aluminide
Source: Scopus
Source-ID: 85055112164

Research output: Contribution to journalArticleScientificpeer-review

Solvent Welding and Imprinting Cellulose Nanofiber Films Using Ionic Liquids

Cellulose nanofiber films (CNFF) were treated via a welding process using ionic liquids (ILs). Acid-base-conjugated ILs derived from 1,5-diazabicyclo[4.3.0]non-5-ene [DBN] and 1-ethyl-3-methylimidazolium acetate ([emim][OAc]) were utilized. The removal efficiency of ILs from welded CNFF was assessed using liquid-state nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared spectroscopy (FTIR). The mechanical and physical properties of CNFF indicated surface plasticization of CNFF, which improved transparency. Upon treatment, the average CNFF toughness increased by 27%, and the films reached a Young's modulus of ∼5.8 GPa. These first attempts for IL "welding" show promise to tune the surfaces of biobased films, expanding the scope of properties for the production of new biobased materials in a green chemistry context. The results of this work are highly relevant to the fabrication of CNFFs using ionic liquids and related solvents.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Paper Converting and Packaging, Universidad Del Bío-Bío, Aalto University
Contributors: Reyes, G., Borghei, M., King, A. W. T., Lahti, J., Rojas, O. J.
Pages: 502-514
Publication date: 14 Jan 2019
Peer-reviewed: Yes
Early online date: 12 Dec 2018

Publication information

Journal: Biomacromolecules
Volume: 20
Issue number: 1
ISSN (Print): 1525-7797
Original language: English
ASJC Scopus subject areas: Bioengineering, Biomaterials, Polymers and Plastics, Materials Chemistry
Source: Scopus
Source-ID: 85059629357

Research output: Contribution to journalArticleScientificpeer-review

A Fast Quench Protection System for High-Temperature Superconducting Magnets

For reaching very high magnetic fields in fully superconducting magnets, beyond 16 T for particle accelerators dipoles and beyond 23 T for solenoids, the use of High-Temperature Superconductors (HTS) is unavoidable. Due to the high Minimum Quench Energy in HTS these coils are much more difficult to protect against quenches using conventional methods such as quench heaters or Coupling Loss Induced Quench (CLIQ). Although it is possible to use a dump resistor on a short HTS magnet, extracting the energy externally, this does not provide a solution for longer magnets or magnets operated in a string, because the extraction voltage becomes unacceptably high. Here a method named E3SPreSSO is proposed that allows for fast energy extraction in HTS magnets. The E3SPreSSO comprises of units with a near-zero self-inductance superconducting circuit, connected in series with the main magnet. When the protection is triggered, these devices are turned resistive, using quench heaters, over-current or CLIQ, causing them to absorb the energy of the system. The units can be located outside the main magnet and do not generate magnetic field. Therefore it is possible to use relatively cost-efficient and robust Nb-Ti or possibly MgB_2 (at higher temperatures). This paper introduces the concept and provides an analytical method weighing the different options for designing the E3SPreSSO units themselves.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, European Organization for Nuclear Research, CERN
Contributors: van Nugteren, J., Murtomäki, J., Ruuskanen, J., Kirby, G., Hagen, P., DeRijk, G., Ten Kate, H., Bottura, L., Rossi, L.
Publication date: Jan 2019
Peer-reviewed: Yes
Early online date: 15 Jun 2018

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 29
Issue number: 1
Article number: 4700108
ISSN (Print): 1051-8223
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Coils, Heating systems, High-temperature superconductors, High-Temperature-Superconductors (HTS), Magnetic circuits, Quench Protection, Resistance, Resistors, Superconducting magnets, Superconducting Magnets, Switch

Bibliographical note

EXT="Murtomäki, Jaakko"

Source: Scopus
Source-ID: 85048658780

Research output: Contribution to journalArticleScientificpeer-review

An Artificial Nocturnal Flower via Humidity-Gated Photoactuation in Liquid Crystal Networks

Beyond their colorful appearances and versatile geometries, flowers can self-shape-morph by adapting to environmental changes. Such responses are often regulated by a delicate interplay between different stimuli such as temperature, light, and humidity, giving rise to the beauty and complexity of the plant kingdom. Nature inspires scientists to realize artificial systems that mimic their natural counterparts in function, flexibility, and adaptation. Yet, many of the artificial systems demonstrated to date fail to mimic the adaptive functions, due to the lack of multi-responsivity and sophisticated control over deformation directionality. Herein, a new class of liquid-crystal-network (LCN) photoactuators whose response is controlled by delicate interplay between light and humidity is presented. Using a novel deformation mechanism in LCNs, humidity-gated photoactuation, an artificial nocturnal flower is devised that is closed under daylight conditions when the humidity level is low and/or the light level is high, while it opens in the dark when the humidity level is high. The humidity-gated photoactuators can be fueled with lower light intensities than conventional photothermal LCN actuators. This, combined with facile control over the speed, geometry, and directionality of movements, renders the “nocturnal actuator” promising for smart and adaptive bioinspired microrobotics.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Eindhoven University of Technology
Contributors: Wani, O. M., Verpaalen, R., Zeng, H., Priimagi, A., Schenning, A. P.
Publication date: Jan 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Advanced Materials
Volume: 31
Issue number: 2
Article number: 1805985
ISSN (Print): 0935-9648
Original language: English
ASJC Scopus subject areas: Materials Science(all), Mechanics of Materials, Mechanical Engineering
Keywords: actuator, azobenzene, bioinspired, humidity, light, liquid crystal, multi-responsive
Source: Scopus
Source-ID: 85056318113

Research output: Contribution to journalArticleScientificpeer-review

Characterization of Powder-Precursor HVOF-Sprayed Al2O3-YSZ/ZrO2 Coatings

Thermal spraying using liquid feedstock can produce coatings with very fine microstructures either by utilizing submicron particles in the form of a suspension or through in situ synthesis leading, for example, to improved tribological properties. The focus of this work was to obtain a bimodal microstructure by using simultaneous hybrid powder-precursor HVOF spraying, where nanoscale features from liquid feedstock could be combined with the robustness and efficiency of spraying with powder feedstock. The nanostructure was achieved from YSZ and ZrO2 solution-precursors, and a conventional Al2O3 spray powder was responsible for the structural features in the micron scale. The microstructures of the coatings revealed some clusters of unmelted nanosized YSZ/ZrO2 embedded in a lamellar matrix of Al2O3. The phase compositions consisted of γ- and α-Al2O3 and cubic, tetragonal and monoclinic ZrO2. Additionally, some alloying of the constituents was found. The mechanical strength of the coatings was not optimal due to the excessive amount of the nanostructured YSZ/ZrO2 addition. An amount of 10 vol.% or 7 wt.% 8YSZ was estimated to result in a more desired mixing of constituents that would lead to an optimized coating architecture.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, ELCOGEN OY, Univ of Oulu
Contributors: Kiilakoski, J., Puranen, J., Heinonen, E., Koivuluoto, H., Vuoristo, P.
Pages: 98-107
Publication date: Jan 2019
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Journal of Thermal Spray Technology
Volume: 28
Issue number: 1-2
ISSN (Print): 1059-9630
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Surfaces, Coatings and Films, Materials Chemistry
Keywords: AlO-ZrO, ceramic matrix composite, coating, HVOF, hybrid, solution-precursor spraying
Source: Scopus
Source-ID: 85058214735

Research output: Contribution to journalArticleScientificpeer-review

Charge carrier dynamics in tantalum oxide overlayered and tantalum doped hematite photoanodes

We employ atomic layer deposition to prepare 50 nm thick hematite photoanodes followed by passivating them with a 0.5 nm thick Ta 2 O 5 -overlayer and compare them with samples uniformly doped with the same amount of tantalum. We observe a three-fold improvement in photocurrent with the same onset voltage using Ta-overlayer hematite photoanodes, while electrochemical impedance spectroscopy under visible light irradiation shows a decreased amount of surface states under water splitting conditions. The Ta-doped samples have an even higher increase in photocurrent along with a 0.15 V cathodic shift in the onset voltage and decreased resistivity. However, the surface state capacitance for the Ta-doped sample is twice that of the reference photoanode, which implies a larger amount of surface hole accumulation. We further utilize transient absorption spectroscopy in the sub-millisecond to second timescale under operating conditions to show that electron trapping in both Ta 2 O 5 -passivated and Ta-doped samples is markedly reduced. Ultrafast transient absorption spectroscopy in the sub-picosecond to nanosecond timescale shows faster charge carrier dynamics and reduced recombination in the Ta-doped hematite photoanode resulting in the increased photoelectrochemical performance when compared with the Ta 2 O 5 -overlayer sample. Our results show that passivation does not affect the poor charge carrier dynamics intrinsic to hematite based photoanodes. The Ta-doping strategy results in more efficient electron extraction, solving the electron trapping issue and leading to increased performance over the surface passivation strategy.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Chemistry & Advanced Materials, Materials Science and Environmental Engineering, Physics, Research group: Surface Science
Contributors: Ruoko, T., Hiltunen, A., Iivonen, T., Ulkuniemi, R., Lahtonen, K., Ali-Löytty, H., Mizohata, K., Valden, M., Leskelä, M., Tkachenko, N. V.
Number of pages: 10
Pages: 3206-3215
Publication date: Jan 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Materials Chemistry A
Volume: 7
Issue number: 7
ISSN (Print): 2050-7488
Original language: English
ASJC Scopus subject areas: Chemistry(all), Renewable Energy, Sustainability and the Environment, Materials Science(all)
Electronic versions: 

Bibliographical note

INT=phys,"Ulkuniemi, Riina"

Source: Scopus
Source-ID: 85061474749

Research output: Contribution to journalArticleScientificpeer-review

Phosphate glasses with blue persistent luminescence prepared using the direct doping method

Phosphate glasses with the composition (90NaPO3-(10-x)Na2O-xNaF) (mol%) with x = 0 and 10 were prepared with blue persistent luminescence (PeL) using direct particles doping method. Commercial CaAl2O4:Eu2+,Nd3+ microparticles (MPs) with blue PeL were added in the glass melt at a lower temperature than the melting temperature. The PeL properties of the glasses were related to the diffusion of Al from the MPs to the glass occurring during the glass preparation, which was found to depend on the temperature at which the MPs are added in the melt and also on the time before casting the melt after adding the MPs. The glass with x = 0 can be prepared with homogeneous PeL if the MPs are added at 575 °C. This Tdoping temperature can be reduced to 550 °C by replacing Na2O by NaF in the glass.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Turun Yliopisto/Turun Biomateriaalikeskus
Contributors: Ojha, N., Tuomisto, M., Lastusaari, M., Petit, L.
Pages: 151-156
Publication date: Jan 2019
Peer-reviewed: Yes
Early online date: 1 Jan 2018

Publication information

Journal: Optical Materials
Volume: 87
ISSN (Print): 0925-3467
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Computer Science(all), Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: CaAlO:Eu,Nd microparticles, Corrosion, Fluorophosphate glass, Persistent luminescence
Source: Scopus
Source-ID: 85044951460

Research output: Contribution to journalArticleScientificpeer-review

1.3μm U-bend traveling wave SOA devices for high efficiency coupling to silicon photonics

We present a U-bend design for traveling wave III-V gain devices, such as semiconductor optical amplifiers and laser diodes. The design greatly simplifies the butt-coupling between the III-V chip and silicon-on-insulator photonic circuit by bringing the I/O ports on one facet. This removes the need for precise dimension control otherwise required for 2-side coupling, therefore increasing the yield of mounted devices towards 100%. The design, fabrication and characterization of the U-bend device based on Euler bend geometry is presented. The losses for a bend with a minimum bending radius of 83 μm are 1.1 dB. In addition, we present an analysis comparing the yield and coupling losses of the traditionally cleaved devices with the results that the Euler bend approach enable, with the final conclusion that the yield is improved by several times while the losses are decreased by several dB.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics, VTT Technical Research Centre of Finland
Contributors: Viheriälä, J., Tuorila, H., Zia, N., Cherchi, M., Aalto, T., Guina, M.
Publication date: 2019

Host publication information

Title of host publication: Silicon Photonics XIV
Publisher: SPIE, IEEE
Editors: Reed, G. T., Knights, A. P.
Article number: 109230E
ISBN (Electronic): 9781510624887

Publication series

Name: Proceedings of SPIE - The International Society for Optical Engineering
Volume: 10923
ISSN (Print): 0277-786X
ISSN (Electronic): 1996-756X
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Computer Science Applications, Applied Mathematics, Electrical and Electronic Engineering
Keywords: Coupling losses, Hybrid integration, III-V, Semiconductor optical amplifiers, Silicon-on-insulator

Bibliographical note

jufoid=71479

Source: Scopus
Source-ID: 85065404814

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

1.55-μm wavelength wafer-fused OP-VECSELs in flip-chip configuration

Optically-pumped vertical external cavity surface emitting lasers (VECSELs) based on flip-chip gain mirrors emitting at the 1.55-μm wavelength range are reported. The gain mirrors employ wafer-fused InAlGaAs/InP quantum well heterostructures and GaAs/AlAs distributed Bragg reflectors, which were incorporated in a linear and a V-cavity configurations. A maximum output power of 3.65 W was achieved for a heatsink temperature of 11°C and employing a 2.2% output coupler. The laser exhibited circular beam profiles for the full emission power range. The demonstration represents more than 10-fold increase of the output power compared to state-of-the-art flip-chip VECSELs previously demonstrated at the 1.55-μm wavelength range, and opens a new perspective for developing practical VECSEL-based laser system for applications such as LIDAR, spectroscopy, communications and distributed sensing.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics, CRPP, LakeDiamond SA
Contributors: Mereuta, A., Nechay, K., Caliman, A., Suruceanu, G., Gallo, P., Guina, M., Kapon, E.
Publication date: 2019

Host publication information

Title of host publication: Vertical External Cavity Surface Emitting Lasers (VECSELs) IX
Publisher: SPIE, IEEE
Editor: Keller, U.
Article number: 1090103
ISBN (Electronic): 9781510624443

Publication series

Name: Proceedings of SPIE - The International Society for Optical Engineering
Volume: 10901
ISSN (Print): 0277-786X
ISSN (Electronic): 1996-756X
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Computer Science Applications, Applied Mathematics, Electrical and Electronic Engineering
Keywords: Optically-pumped VECSELs, Semiconductor lasers, Wafer-Fusion

Bibliographical note

jufoid=71479

Source: Scopus
Source-ID: 85066636665

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

405-nm pumped Ce 3+ -doped silica fiber for broadband fluorescence from cyan to red

A pure Ce-doped silica fiber is fabricated using modified chemical vapor deposition (MCVD) technique. Fluorescence characteristics of a Ce-doped silica fiber are experimentally investigated with continuous wave pumping from 440 nm to 405 nm. Best pump absorption and broad fluorescence spectrum is observed for ∼ 405 nm laser. Next, the detailed analysis of spectral response as a function of pump power and fiber length is performed. It is observed that a-10dB spectral width of ∼ 280 mn can be easily achieved with different combinations of the fiber length and pump power. Lastly, we present, for the first time to the best of our knowledge, a broadband fluorescence spectrum with-10dB spectral width of 301 nm, spanning from ∼ 517.36 nm to ∼ 818 nm, from such fibers with non-UV pump lasers.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics, Aston University, Fiber Optics Research Center of the Russian Academy of Sciences, Russian Academy of Sciences
Contributors: Yadav, A., Chichkov, N. B., Gumenyuk, R., Zherebtsov, E., Melkumov, M. A., Yashkov, M. V., Dianov, E. M., Rafailov, E. U.
Publication date: 2019

Host publication information

Title of host publication: Optical Components and Materials XVI
Publisher: SPIE, IEEE
Editors: Digonnet, M. J. F., Jiang, S.
Article number: 1091406
ISBN (Electronic): 9781510624702

Publication series

Name: Proceedings of SPIE - The International Society for Optical Engineering
Volume: 10914
ISSN (Print): 0277-786X
ISSN (Electronic): 1996-756X
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Computer Science Applications, Applied Mathematics, Electrical and Electronic Engineering
Keywords: Broadband spectrum, Ce-doped fiber, Ce-ion, Rare earth doped

Bibliographical note

jufoid=71479

Source: Scopus
Source-ID: 85066046508

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Analysis of hygrothermal parameters in Finnish and Lithuanian multi-family buildings before and after energy retrofits

This study focuses on analyzing temperature- and moisture-related parameters based on data from 45 Finnish and 20 Lithuanian multi-family buildings. The data consist of two rounds of 2-month data-logging (1-h interval) of indoor temperature and relative humidity at two locations: one representing average occupied zone and the other one nearby the coldest spot of the building envelope. Between the two rounds of data-logging, 37 buildings from Finland and 15 buildings from Lithuania underwent retrofits, aiming to improve their energy efficiency. Measurement data were coupled with outdoor data from national weather stations, based on which a temperature factor (fc) and excess indoor moisture content (Δv) were calculated. Based on the results, fc was significantly higher in Lithuanian case buildings after the retrofits, whereas no significant differences were observed in Finnish buildings. In addition, Δv was significantly lower in Finnish case buildings after retrofits, whereas an opposite trend was seen in the Lithuanian buildings.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Civil Engineering, Research group: Concrete and Bridge Structures, Kaunas University of Technology, National Public Health Institute
Contributors: Leivo, V., Kiviste, M., Aaltonen, A., Prasauskas, T., Martuzevicius, D., Haverinen-Shaughnessy, U.
Number of pages: 17
Publication date: 2019
Peer-reviewed: Yes
Early online date: 1 Apr 2018

Publication information

Journal: Journal of Building Physics
Volume: 42
Issue number: 4
ISSN (Print): 1744-2591
Original language: English
ASJC Scopus subject areas: Building and Construction, Materials Science(all)
Keywords: indoor moisture excess, relative humidity, surface temperature, Temperature, temperature factor
Source: Scopus
Source-ID: 85045857327

Research output: Contribution to journalArticleScientificpeer-review

An automated algorithm for reliable equation of state fitting of magnetic systems

In computational physics and materials science ground-state properties are often extracted from an equation of state fit to energy-volume data. Magnetic systems often have multiple magnetic phases present in the energy-volume data, which poses a challenge for the fitting approach because the results are sensitive to the selection of included fitting points. This is because practically all popular equation of state fitting functions, such as Murnaghan and Birch-Murnaghan, assume just one phase and therefore cannot correctly fit magnetic energy-volume data that contains multiple phases. When fitting magnetic energy-volume data it is therefore important to select the range of fitting points in such a way that only points from the one relevant phase are included. We present a simple algorithm that makes the point selection automatically. Selecting fitting points automatically removes human bias and should also be useful for large-scale projects where selecting all fitting points by hand is not feasible.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research area: Computational Physics, Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, Uppsala University, Department of Physics and Astronomy, University of Turku, Royal Institute of Technology
Contributors: Levämäki, H., Tian, L., Vitos, L., Ropo, M.
Number of pages: 8
Pages: 121-128
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Computational Materials Science
Volume: 156
ISSN (Print): 0927-0256
Original language: English
ASJC Scopus subject areas: Computer Science(all), Chemistry(all), Materials Science(all), Mechanics of Materials, Physics and Astronomy(all), Computational Mathematics
Keywords: EOS, Equation of state fitting
Source: Scopus
Source-ID: 85053772857

Research output: Contribution to journalArticleScientificpeer-review

Antibacterial polymer fibres by rosin compounding and melt-spinning

The antibacterial features of natural pine/spruce rosin are well established, yet the functionality in various thermoplastics has not been surveyed. This work focuses on the processing of industrial grade purified rosin mixed with polyethylene (PE), polypropylene (PP), polylactic acid (PLA), polyamide (PA)and corn starch based biopolymer (CS). Homopolymer masterbatches were extrusion-compounded and melt-spun to form fibres for a wide range of products, such as filters, reinforcements, clothing and medical textiles. Due to the versatile chemical structure of rosin, it was observed compatible with all the selected polymers. In general, the rosin-blended systems were shear-thinning in a molten condition. The doped fibres spun of PE and PP indicated adequate melt-spinning capability and proper mechanical properties in terms of ultimate strength and Young's modulus. The antibacterial response was found dependent on the selected polymer. Especially PE with a 10 wt% rosin content showed significant antibacterial effects against Escherichia coli DH5α and Staphylococcus aureus ATCC 12598 when analysed in the Ringer's solution for 24 h.

General information

Publication status: Accepted/In press
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Research group: Plastics and Elastomer Technology, Department of Microbiology, Bundesanstalt für Materialforschung und -prüfung (BAM), Premix Oy, Aalto University, COMP Centre of Excellence, University of Helsinki
Contributors: Kanerva, M., Puolakka, A., Takala, T. M., Elert, A. M., Mylläri, V., Jönkkäri, I., Sarlin, E., Seitsonen, J., Ruokolainen, J., Saris, P., Vuorinen, J.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Materials Today Communications
Article number: 100527
ISSN (Print): 2352-4928
Original language: English
ASJC Scopus subject areas: Materials Science(all), Mechanics of Materials, Materials Chemistry
Keywords: Antibacterial, Fibre, Melt spinning, Thermoplastics
Electronic versions: 

Bibliographical note

EXT="Mylläri, V."

Source: Scopus
Source-ID: 85066275027

Research output: Contribution to journalArticleScientificpeer-review

Behaviour of leaded tin bronze in simulated seawater in the absence and presence of tribological contact with alumina counterbody: Corrosion, wear and tribocorrosion

Corrosion, wear and tribocorrosion behaviours of leaded tin bronze were examined in simulated seawater using alumina counterbody for tribological contact. Active dissolution of alloy and corrosion product development on surfaces were the dominant corrosion mechanisms. Tribological contact with counterbody removed majority of the products, thus contributing to active dissolution of freshly exposed surface. This wear-induced corrosion mechanism contributed to 45% and 60% of total material losses at the two highest potentials, 50 mV and 250 mV vs. Ag/AgCl. Pure wear of alloy occurred in the form of abrasive wear. At anodic potentials under tribological contact, corrosion raised the friction coefficient as compared to pure wear and increased wear of the alloy. These results are presented and discussed in this paper.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, VTT Technical Research Centre of Finland
Contributors: Huttunen-Saarivirta, E., Isotahdon, E., Metsäjoki, J., Salminen, T., Ronkainen, H., Carpén, L.
Number of pages: 15
Pages: 257-271
Publication date: 2019
Peer-reviewed: Yes
Early online date: 22 Aug 2018

Publication information

Journal: Tribology International
Volume: 129
ISSN (Print): 0301-679X
Original language: English
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Surfaces and Interfaces, Surfaces, Coatings and Films
Keywords: Contact: sliding, Surface: chemical analysis, Synergism: tribochemistry, Wear: corrosive

Bibliographical note

EXT="Metsäjoki, J."
EXT="Isotahdon, E."

Source: Scopus
Source-ID: 85052665246

Research output: Contribution to journalArticleScientificpeer-review

Charge transfer dynamics in CsPbBr3 perovskite quantum dots-anthraquinone/fullerene (C60) hybrids

An advantage of colloidal quantum dots, particularly perovskite quantum dots (PQDs), as photoactive components is that they easily form complexes with functional organic molecules, which results in hybrids with enriched photophysical properties. Herein, we demonstrate the formation of stable ground state complexes of CsPbBr3 PQD with two widely used molecular electron acceptors, fullerene (C60) and anthraquinone, (AQ) which contain carboxylic anchor groups. Dynamics of the photo-induced electron transfer in the hybrids were compared. The use of carboxylic groups for binding results in stable complex formation and their photophysical properties depend on the ratio of components but not the absolute concentrations (up to micromolar concentrations). Time-resolved transient absorption (TA) spectroscopy shows that in both cases, a charge separated (CS) state is formed. Data analysis was aimed to evaluate the CS time constant in ideal one-to-one complexes and was found to be in the range of 30-190 ps. The CS state of PQD-AQ complexes recombines directly to the ground state in roughly one microsecond. Recombination of the CS state of PQD-C60 is more complex and points to strong inhomogeneity of these complexes. Majority of the CS states relax by first forming the C60 triplet state.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering
Contributors: Mandal, S., George, L., Tkachenko, N. V.
Number of pages: 8
Pages: 862-869
Publication date: 2019
Peer-reviewed: Yes
Early online date: 10 Dec 2018

Publication information

Journal: Nanoscale
Volume: 11
Issue number: 3
ISSN (Print): 2040-3364
Original language: English
ASJC Scopus subject areas: Materials Science(all)
Source: Scopus
Source-ID: 85060171357

Research output: Contribution to journalArticleScientificpeer-review

Crystallography and Mechanical Properties of Intercritically Annealed Quenched and Partitioned High-Aluminium Steel

The quenching and partitioning response of intercritically annealed steel with aluminum contents in the 2–3 wt.% range and a carbon content of 0.2 wt.% was studied. Two types of morphologies for retained austenite were observed in electron backscatter diffraction studies: blocky, untransformed austenite grains and partially transformed austenite located primarily at prior austenite and packet boundaries. The amount of retained austenite was found to correlate with the initial quench temperature, as well as with the uniform elongation of the specimens in subsequent tensile testing. The transformation characteristics of austenite were rationalized on the basis of prior austenite grain size and inhomogeneous carbon distribution. The martensite transformed during the initial quench was found to favor Σ3 twin-type lath combinations, supplemented by neighboring variants providing self-accommodation.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Metals Technology, Materials Science, Colorado School of Mines, Golden, CO 80401 USA, Outotec Oyj
Contributors: Nyyssönen, T., Peura, P., De Moor, E., Kuokkala, V., Williamson, D. L.
Number of pages: 31
Publication date: 2019
Peer-reviewed: Yes
Early online date: 11 Dec 2018

Publication information

Journal: Materials Characterization
ISSN (Print): 1044-5803
Original language: English
ASJC Scopus subject areas: Metals and Alloys
Keywords: steels, crystallography, mechanical properties, microstructure, martensite

Bibliographical note

EXT="Nyyssönen, Tuomo"

Research output: Contribution to journalArticleScientificpeer-review

Design, processing, and characterization of an optical core-bioactive clad phosphate fiber for biomedical applications

The aim of this study was to fabricate a bioactive optical fiber able to monitor “in situ” its reaction with the body through changes in its optical properties. Core and cladding preforms were prepared with the composition (97.25*(0.50P2O5-0.40SrO-0.10Na2O)-2.5ZnO-0.25Er2O3) and (98.25*(0.50P2O5-0.40SrO-0.10Na2O)-1.75ZnO) (in mol%), respectively, and successfully drawn into a multimode core/clad optical fiber. Optical and near-Infrared images assessed the proper light guiding properties of the fiber. The fibers favor the precipitation of a Ca-P reactive layer at its surface concomitant with a reduction in the fiber diameter, when immersed in SBF, often assigned as a sign of bioactivity. It is clearly shown here that the bio-response of the fiber upon immersion in SBF can be tracked from the decrease in the intensity of the Er3+ ions emission at 1.5 µm. This confirms that the newly developed optical fiber, which combines good optical properties with a suitable bioactive behavior, is a promising platform for the development of novel biomedical devices for biophotonic and photomedical applications. Finally, the successful splicing of the newly developed fiber with commercial optical fibers was an evidence of the possibility to integrate the newly developed phosphate fiber within existing components used in the field of biomedicine.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, BioMediTech, Politecnico di Torino, Fondazione LINKS – Leading Innovation & Knowledge for Society, UMR CNRS 6226 Sciences Chimiques de Rennes, University of Parma, Photonics Laboratory
Contributors: Lopez-Iscoa, P., Ojha, N., Pugliese, D., Mishra, A., Gumenyuk, R., Boetti, N. G., Janner, D., Troles, J., Bureau, B., Boussard-Plédel, C., Massera, J., Milanese, D., Petit, L.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: JOURNAL OF THE AMERICAN CERAMIC SOCIETY
ISSN (Print): 0002-7820
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Materials Chemistry
Keywords: bioactivity, Er luminescence property, optical fiber, phosphate glass
Source: Scopus
Source-ID: 85066458189

Research output: Contribution to journalArticleScientificpeer-review

Flip-chip Wafer-fused OP-VECSELs emitting 3.65 W at the 1.55-&#x03BC;m waveband

Optically-pumped vertical external cavity surface emitting lasers (VECSELs) based on flip-chip gain mirrors emitting at the 1.55-&#x03BC;m wavelength range are reported. The gain mirrors employ wafer-fused InAlGaAs/InP quantum well heterostructures and GaAs/AlAs distributed Bragg reflectors fixed on a diamond heat-sink substrate in a flip-chip geometry, incorporated in a V-cavity configuration. A maximum output power of 3.65 W was achieved for a heat sink temperature of 11&#x00B0;C and employing a 2.2% output coupler. The laser exhibited circular beam profiles for the full emission power range. This demonstration represents more than 5-fold increase of the output power compared to state-of-the-art flip-chip VECSELs previously reported at the 1.55 &#x03BC;m wavelength range. It opens new perspectives for developing practical VECSEL-based laser systems operating at a wavelength range widely used in many applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, CRPP, LakeDiamond SA
Contributors: Mereuta, A., Nechay, K., Caliman, A., Suruceanu, G., Rudra, A., Gallo, P., Guina, M., Kapon, E.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Journal of Selected Topics in Quantum Electronics
Volume: 25
Issue number: 6
ISSN (Print): 0792-1233
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Atomic and Molecular Physics, and Optics, Materials Chemistry, Electrical and Electronic Engineering
Keywords: diode pumped, Flip-chip devices, Heating systems, Lasers, Mirrors, Optical pumping, Power generation, Semiconductor lasers, Temperature measurement, Vertical cavity surface emitting lasers, Vertical emitting lasers
Source: Scopus
Source-ID: 85067801249

Research output: Contribution to journalArticleScientificpeer-review

Gas-foamed poly(lactide-co-glycolide) and poly(lactide-co-glycolide) with bioactive glass fibres demonstrate insufficient bone repair in lapine osteochondral defects

Deep osteochondral defects may leave voids in the subchondral bone, increasing the risk of joint structure collapse. To ensure a stable foundation for the cartilage repair, bone grafts can be used for filling these defects. Poly(lactide-co-glycolide) (PLGA) is a biodegradable material that improves bone healing and supports bone matrix deposition. We compared the reparative capacity of two investigative macroporous PLGA-based biomaterials with two commercially available bone graft substitutes in the bony part of an intra-articular bone defect created in the lapine femur. New Zealand white rabbits (n = 40) were randomized into five groups. The defects, 4 mm in diameter and 8 mm deep, were filled with neat PLGA; a composite material combining PLGA and bioactive glass fibres (PLGA–BGf); commercial beta-tricalcium phosphate (β-TCP) granules; or commercial bioactive glass (BG) granules. The fifth group was left untreated for spontaneous repair. After three months, the repair tissue was evaluated with X-ray microtomography and histology. Relative values comparing the operated knee with its contralateral control were calculated. The relative bone volume fraction (∆BV/TV) was largest in the β-TCP group (p ≤ 0.012), which also showed the most abundant osteoid. BG resulted in improved bone formation, whereas defects in the PLGA–BGf group were filled with fibrous tissue. Repair with PLGA did not differ from spontaneous repair. The PLGA, PLGA–BGf, and spontaneous groups showed thicker and sparser trabeculae than the commercial controls. We conclude that bone repair with β-TCP and BG granules was satisfactory, whereas the investigational PLGA-based materials were only as good as or worse than spontaneous repair.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, University of Helsinki Faculty of Medicine, Helsinki University Central Hospital, Department of Medical Physics, Tampere University Hospital, Abo Akad Univ, Abo Akademi University, Dept Phys
Contributors: Salonius, E., Muhonen, V., Lehto, K., Järvinen, E., Pyhältö, T., Hannula, M., Aula, A. S., Uppstu, P., Haaparanta, A. M., Rosling, A., Kellomäki, M., Kiviranta, I.
Number of pages: 10
Pages: 406-415
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Tissue Engineering and Regenerative Medicine
Volume: 13
Issue number: 3
ISSN (Print): 1932-6254
Original language: English
ASJC Scopus subject areas: Medicine (miscellaneous), Biomaterials, Biomedical Engineering
Keywords: animal model, biomaterial, bone repair, intra-articular, poly(lactide-co-glycolide)
Source: Scopus
Source-ID: 85061916720

Research output: Contribution to journalArticleScientificpeer-review

Human Neural Tissues from Neural Stem Cells Using Conductive Biogel and Printed Polymer Microelectrode Arrays for 3D Electrical Stimulation

Electricity is important in the physiology and development of human tissues such as embryonic and fetal development, and tissue regeneration for wound healing. Accordingly, electrical stimulation (ES) is increasingly being applied to influence cell behavior and function for a biomimetic approach to in vitro cell culture and tissue engineering. Here, the application of conductive polymer (CP) poly(3,4-ethylenedioxythiophene)-polystyrenesulfonate (PEDOT:PSS) pillars is described, direct-write printed in an array format, for 3D ES of maturing neural tissues that are derived from human neural stem cells (NSCs). NSCs are initially encapsulated within a conductive polysaccharide-based biogel interfaced with the CP pillar microelectrode arrays (MEAs), followed by differentiation in situ to neurons and supporting neuroglia during stimulation. Electrochemical properties of the pillar electrodes and the biogel support their electrical performance. Remarkably, stimulated constructs are characterized by widespread tracts of high-density mature neurons and enhanced maturation of functional neural networks. Formation of tissues using the 3D MEAs substantiates the platform for advanced clinically relevant neural tissue induction, with the system likely amendable to diverse cell types to create other neural and non-neural tissues. The platform may be useful for both research and translation, including modeling tissue development, function and dysfunction, electroceuticals, drug screening, and regenerative medicine.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Computational Biophysics and Imaging Group, BioMediTech, University of Wollongong, The University of Auckland, Department of Chemistry and Bioengineering, MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Melbourne
Contributors: Tomaskovic-Crook, E., Zhang, P., Ahtiainen, A., Kaisvuo, H., Lee, C. Y., Beirne, S., Aqrawe, Z., Svirskis, D., Hyttinen, J., Wallace, G. G., Travas-Sejdic, J., Crook, J. M.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: ADVANCED HEALTHCARE MATERIALS
Article number: 1900425
ISSN (Print): 2192-2640
Original language: English
ASJC Scopus subject areas: Biomaterials, Biomedical Engineering, Pharmaceutical Science
Keywords: 3D electrical stimulation, conductive biogels, human neural tissue, printed conducting polymer electrodes, stem cells
Source: Scopus
Source-ID: 85067695878

Research output: Contribution to journalArticleScientificpeer-review

Impact wear and mechanical behavior of steels at subzero temperatures

In this study, the deformation behavior of three steels was studied at Arctic temperatures by controlled single and multiple oblique angle impacts. The results were compared with the mechanical properties of the steels determined at the corresponding temperatures. At subzero temperatures, the hardness and strength of the studied steels increased and their ability to deform plastically steadily decreased. In the martensitic steels, adiabatic shear bands were observed to form during the impacts at subzero temperatures, indicating that the deformation ability of the steels was critically impaired. At −60 °C, the adiabatic shear bands commonly acted as initiation sites for subsurface cracks. Moreover, the surface characterization of the test samples revealed formation of cracks and wear particles, which was connected to the opening of grain boundaries and martensite laths at low temperatures. Finite Element Modeling was also used to obtain more information about the impact event.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Materials Characterization, University of Nottingham
Contributors: Valtonen, K., Ratia, V., Ramakrishnan, K. R., Apostol, M., Terva, J., Kuokkala, V.
Number of pages: 18
Pages: 476-493
Publication date: 2019
Peer-reviewed: Yes
Early online date: 17 Aug 2018

Publication information

Journal: Tribology International
Volume: 129
ISSN (Print): 0301-679X
Original language: English
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Surfaces and Interfaces, Surfaces, Coatings and Films
Keywords: Impact, Low temperature, Steel, Wear
Electronic versions: 
Source: Scopus
Source-ID: 85053014382

Research output: Contribution to journalArticleScientificpeer-review

Integrated Use of Licensed-and Unlicensed-Band mmWave Radio Technology in 5G and beyond

The 3GPP standardization rapidly moves forward with studies of a wide-bandwidth waveform as well as an adaptation of the emerging 5G new radio (NR)-based access to the unlicensed spectrum (NR-U). One of the basic architectures for NR-U involves carrier aggregation of an anchor-licensed-NR carrier and a secondary carrier in unlicensed spectrum, which altogether allows for seamless traffic offloading in scenarios where multi-gigabit data rates are required. While today's research on NR-U addresses mostly physical-and protocol-layer aspects, a system-level performance of the NR-U offloading mechanisms has not been investigated thoroughly. In this paper, we develop a mathematical queuing-Theoretic framework that is mindful of the specifics of millimeter-wave (mmWave) session dynamics and may serve as a flexible tool for the analysis of various strategies for the integrated use of licensed and unlicensed mmWave bands in terms of the session drop probability and system utilization. To illustrate this, we select three distinct strategies (based on sequential service, probabilistic offloading, or proportional splitting), and complement our mathematical models with a detailed performance evaluation in a representative massive augmented/virtual reality scenario. Based on this quantitative analysis of the selected schemes, we conclude that proportional splitting of traffic between the two mmWave bands leads to a better performance. We believe that the contributed mathematical analysis can become an important building block in further system development and service optimization across many usage scenarios.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, King’s College London, Peoples’ Friendship University of Russia, Department of Applied Mathematics and Probability Theory
Contributors: Lu, X., Sopin, E., Petrov, V., Galinina, O., Moltchanov, D., Ageev, K., Andreev, S., Koucheryavy, Y., Samouylov, K., Dohler, M.
Number of pages: 16
Pages: 24376-24391
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Access
Volume: 7
ISSN (Print): 2169-3536
Original language: English
ASJC Scopus subject areas: Computer Science(all), Materials Science(all), Engineering(all)
Keywords: 5G and beyond, 5G-U, integration of licensed and unlicensed bands, massive AR/VR, mathematical analysis, mmWave-based access, NR-U, radio resource allocation
Source: Scopus
Source-ID: 85062961977

Research output: Contribution to journalArticleScientificpeer-review

In-vitro dissolution characteristics and human adipose stem cell response to novel borophosphate glasses

The main drawbacks of traditional silicate bioactive glasses are their narrow hot forming domain and noncongruent dissolution. In this article, we report on new borophosphate glasses [xMnOm + (100 − x) (47.5P2O5 + 2.5B2O3 + 10Na2O + 20CaO + 20SrO)], MnOm being CuO, Ag2O, and CeO2, having high thermal processability, hence suitable for fiber drawing and sintering into scaffolds. Furthermore, the glasses dissolve congruently in simulated body fluid (SBF) and TRIS buffer solution, eventually leading to the precipitation of a reactive layer. Human adipose stem cells (hASC) were cultured in media enriched with glass extract at different dilutions, to investigate the optimal ion concentration for cell survival. Cells grew in all the extracts, except in the undiluted Cu-doped glass extract. At dilution 1:10, the lactate dehydrogenase (LDH) activity and cell proliferation were comparable to the control, while at 1:100, the cells proliferated faster than the control. Thus, the reference (undoped), Ag and Ce-doped glasses were found to be suitable for cell viability and proliferation. Cytotoxicity assessments using the LDH assay indeed revealed the high cytotoxicity of the Cu extract. This raises questions about the use of Cu in bioactive glasses and its optimal concentration as a dopant.

General information

Publication status: Accepted/In press
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Health Sciences, Karolinska Institutet, Adult Stem Cell Group, Tampere University, Tampere University Hospital
Contributors: Mishra, A., Ojansivu, M., Autio, R., Vanhatupa, S., Miettinen, S., Massera, J.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Biomedical Materials Research - Part A
ISSN (Print): 1549-3296
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Biomaterials, Biomedical Engineering, Metals and Alloys
Keywords: bioactive glass, borophosphate glass, cell proliferation, cytotoxicity, in-vitro dissolution

Bibliographical note

EXT="Ojansivu, Miina"

Source: Scopus
Source-ID: 85066908676

Research output: Contribution to journalArticleScientificpeer-review

Low-dimensional formamidinium lead perovskite architectures via controllable solvent intercalation

We report the formation of a new class of solvent-intercalated two-dimensional (SI-2D) formamidinium lead halide perovskites. They can be mixed with three-dimensional (3D) stoichiometric perovskites by controlling the ratio of the precursor solutions. The composite leads to greatly improved photoluminescence quantum yield (PLQY) over the 3D compound. The enhanced PLQY is attributed to a type-I band alignment between the 3D and SI-2D, as revealed by first-principles calculations, which results in confined excitons with enhanced radiative recombination. The films exhibited excellent thermal and air stability retaining PLQY > 20% over 2 months in ambient conditions. Assemblies of halide perovskites with mixed dimensionality offer a pathway to enhance optoelectronic performance and device lifetimes.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering, Korea Advanced Institute of Science and Technology (KAIST), Yonsei University
Contributors: Shin, M., Kim, J., Jung, Y. K., Ruoko, T., Priimagi, A., Walsh, A., Shin, B.
Number of pages: 7
Pages: 3945-3951
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Materials Chemistry C
Volume: 7
Issue number: 13
ISSN (Print): 2050-7534
Original language: English
ASJC Scopus subject areas: Chemistry(all), Materials Chemistry
Source: Scopus
Source-ID: 85064717293

Research output: Contribution to journalArticleScientificpeer-review

MECSELs with direct emission in the 760 nm to 810 nm spectral range: A single- and double-side pumping comparison and high-power continuous-wave operation

We compared single-side pumping (SSP) and double-side pumping (DSP) of a semiconductor membrane external-cavity surface-emitting laser (MECSEL). The MECSEL's active region was based on a 4×3 AlGaAs quantum well (QW) structure. This structure was embedded between two silicon carbide (SiC) wafer pieces that were used as transparent intra-cavity (IC) heat spreaders creating a symmetrical cooling environment. The MECSEL structure targeted emission at 780nm and was operated at 20°C heat sink temperature. Via DSP the differential efficiency was improved from 31.9% to 34.4 %. The laser threshold was reduced from 0.79 W to 0.69 W of absorbed pump power while the maximum output power was increased from 3.13 W to 3.22 W. The DSP configuration enabled these improvements by a reduced thermal resistance of the gain element by 9 %. The MECSEL operated at a fundamental Gaussian TEM00 mode profile and the beam quality was measured to be M2 <1.09. We further demonstrate a maximum tuning range from 767 nm to 811 nm. A similar active region with about half the thickness (2×3 AlGaAs QWs) was investigated using the DSP configuration and first results are presented here. 500-μm-thick sapphire IC heat spreaders were used instead of SiC. The output power exceeded 0.5W and the emission was spectrally located around 770 nm.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics
Contributors: Kahle, H., Penttinen, J. P., Phung, H. M., Rajala, P., Tukiainen, A., Ranta, S., Guina, M.
Publication date: 2019

Host publication information

Title of host publication: Vertical External Cavity Surface Emitting Lasers (VECSELs) IX
Publisher: SPIE, IEEE
Editor: Keller, U.
Article number: 109010D
ISBN (Electronic): 9781510624443

Publication series

Name: Proceedings of SPIE - The International Society for Optical Engineering
Volume: 10901
ISSN (Print): 0277-786X
ISSN (Electronic): 1996-756X
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Computer Science Applications, Applied Mathematics, Electrical and Electronic Engineering
Keywords: AlGaAs, DBR-free, MECSEL, Near infra-red, Thermal management, Thermal resistance, VECSEL

Bibliographical note

INT=phys,"Rajala, Patrik"
jufoid=71479

Source: Scopus
Source-ID: 85066635597

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Microstructure-property relationships of novel ultra-high strength press hardening steels

The industrial significance of microalloyed martensitic steels manufactured via cold rolling, reaustenitization, and quenching has been typically recognized as low. However, it is currently believed that microalloying can improve the in-service properties of ultra-high-strength press hardening steels. In this work, five 34MnB5-based steels were designed to address the role of Ti and V when combined with Cr or Mo. Microstructure-property relationships were analyzed after die quenching and additional bake hardening (BH) heat treatment using advanced methods of microscopy, glow discharge optical emission spectroscopy, quasi-static tensile tests, and three-point bending tests. Results indicate that both Ti and V can provide grain size refinement through the formation of stabile nanosized precipitates. The BH treatment improved postuniform elongation values, indicating a trend of improved ductility. However, the expected improvements in bendability were clearly confirmed only for two V-microalloyed steels with the alloying concepts of 0.3Cr-0.15V-0.03Al-0.02Ti-0.0020B and 0.3Mo-0.15V-0.0060N (without Al-Ti-B additions) (wt pct). Thus, it was discovered that microalloying with V, when combined with either Cr or Mo, provides a promising combination of mechanical properties as far as the austenitization parameters are appropriately controlled.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Metals Technology, Research group: Materials Characterization, SSAB Europe Oy
Contributors: Järvinen, H., Honkanen, M., Oja, O., Järvenpää, M., Peura, P.
Number of pages: 21
Pages: 816-836
Publication date: 2019
Peer-reviewed: Yes
Early online date: 29 Nov 2018

Publication information

Journal: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume: 50
Issue number: 2
ISSN (Print): 1073-5623
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Mechanics of Materials, Metals and Alloys
Keywords: Press hardening, Bake hardening, Martensite, EBSD, TEM, Mechanical behavior

Research output: Contribution to journalArticleScientificpeer-review

Multiphoton Excitation of CsPbBr3 Perovskite Quantum Dots (PQDs): How Many Electrons Can One PQD Donate to Multiple Molecular Acceptors?

Metastable multiexcitonic states (MESs) of semiconductor quantum dots can be involved in multielectron transfer reactions, which opens new perspectives in nanomaterials-based optoelectronic applications. Herein, we demonstrate the generation of a MES in CsPbBr3 perovskite quantum dots (PQDs) and its dissociation dynamics through multiple electron transfers to molecular electron acceptors, anthraquinones (AQs), bound to the PQD surface by a carboxylic anchor. As many as 14 excitons are produced at an excitation density of roughly 220 μJ cm-2 without detectable PQD degradation. Addition of AQ results in the formation of PQD-AQ hybrids with excess of AQs (PQD:AQ ≈ 1:20), which opens the possibility of multielectron transfer acts from MES to AQs. We found that the electron transfer saturates after roughly five transfer acts and that the first electron transfer (ET) time constant is as short as 1 ps. However, each ET increases the Coulomb potential barrier for the next ET, which decreases the rate of ET, resulting in a saturation after five ETs.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Bio- and Circular Economy, Materials Science and Environmental Engineering
Contributors: Mandal, S., Tkachenko, N. V.
Number of pages: 7
Pages: 2775-2781
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry Letters
ISSN (Print): 1948-7185
Original language: English
ASJC Scopus subject areas: Materials Science(all), Physical and Theoretical Chemistry
Electronic versions: 
Source: Scopus
Source-ID: 85066897133

Research output: Contribution to journalArticleScientificpeer-review

Observation of local electroluminescent cooling and identifying the remaining challenges

The cooling of a light emitting diode (LED) by photons carrying out more energy than was used to electrically bias the device, has been predicted decades ago. 1, 2 While this effect, known as electroluminescent cooling (ELC), may allow e.g. fabricating thermophotonic heat pumps (THP) providing higher efficiencies than the existing solid state coolers, 3 ELC at powers sufficient for practical applications is still not demonstrated. To study high-power ELC we use double diode structures (DDSs), which consist of a double heterojunction (DHJ) LED and a photodiode (PD) grown within a single technological process and, thus, enclosed in a cavity with a homogeneous refractive index. 4, 5 The presence of the PD in the structure allows to more directly probe the efficiency of the LED, without the need for light extraction from the system, reducing undesirable losses. Our analysis of experimentally measured I - V curves for both the LED and the PD suggests that the local efficiency of the high-performance LEDs we have fabricated is approximately 110%, exceeding unity over a wide range of injection current densities of up to about 100A/cm 2 . At present the efficiency of the full DDS, however, still falls short of unity, not allowing direct evidence of the extraction of thermal energy from the LED. Here we review our previous studies of DDS for high-power EL cooling and discuss in more detail the remaining bottlenecks for demonstrating high-power ELC in the DDS context: the LED surface states, resistive and photodetection losses. In particular we report our first surface passivation measurements. Further optimization therefore mainly involves reducing the influence of the surface states, e.g. using more efficient surface passivation techniques and optimizing the PD. This combined with the optimization of the DDS layer thicknesses and contact metallization schemes is expected to finally allow purely experimental observation of high-power ELC.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Physics, Aalto University
Contributors: Radevici, I., Sadi, T., Tripurari, T., Tiira, J., Ranta, S., Tukiainen, A., Guina, M., Oksanen, J.
Publication date: 2019

Host publication information

Title of host publication: Photonic Heat Engines : Science and Applications
Publisher: SPIE, IEEE
Editors: Seletskiy, D. V., Epstein, R. I., Sheik-Bahae, M.
Article number: 109360A
ISBN (Electronic): 9781510625143

Publication series

Name: Proceedings of SPIE - The International Society for Optical Engineering
Volume: 10936
ISSN (Print): 0277-786X
ISSN (Electronic): 1996-756X
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Computer Science Applications, Applied Mathematics, Electrical and Electronic Engineering
Keywords: Double diode structures, Electroluminescent cooling, III-V semiconductors, Quantum efficiency, Surface states

Bibliographical note

jufoid=71479

Source: Scopus
Source-ID: 85065604697

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

On the limit of superhydrophobicity: Defining the minimum amount of TiO2 nanoparticle coating

Fabrication of superhydrophobic surfaces in large scale has been in high interest for several years, also titanium oxide nanostructures having been applied for the purpose. Optimizing the amount and structure of the TiO2 material in the coating will play a key role when considering upscaling. Here, we take a look at fabricating the superhydrophobic surface in a one-step roll-to-roll pilot scale process by depositing TiO2 nanoparticles from a Liquid Flame Spray onto a moving paperboard substrate. In order to find the minimum amount of nanomaterial still sufficient for creating superhydrophobicity, we varied nanoparticle production rate, flame distance from the substrate and line speed. Since the deposited amount of material sideways from the flame path was seen to decrease gradually, spatial analysis enabled us to consistently determine the minimum amount of TiO2 nanoparticles on the substrate needed to achieve superhydrophobicity. Amount as low as 20-30 mg m-2 of TiO2 nanoparticles was observed to be sufficient. The scanning electron microscopy revealed that at this amount, the surface was covered with nanoparticles only partially, but still sufficiently to create a hierarchical structure to affect wetting significantly. Based on XPS analysis, it became apparent that TiO2 gathers hydrocarbons on the surface to develop the surface chemistry towards hydrophobic, but below the critical amount of TiO2 nanoparticles, the chemistry could not enable superhydrophobicity anymore. While varying the deposited amount of TiO2, besides the local spatial variance of the coating amount, also the overall yield was studied. Within the text matrix, a yield up to 44% was achieved. In conclusion, superhydrophobicity was achieved at all tested line speeds (50 to 300 m min-1), even if the amount of TiO2 varied significantly (20 to 230 mg m-2).

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Aerosol Synthesis, Research area: Aerosol Physics, Materials Science, Packaging Technology Research Team, Physics at Interfaces, Max Planck Institute for Polymer Research, Bioscience and Materials/Surface, RISE Research Institutes of Sweden AB, Finnish Environment Institute, Abo Akad Univ, Abo Akademi University, Dept Phys, AGH University of Science and Technology, University of Eastern Finland
Contributors: Haapanen, J., Aromaa, M., Teisala, H., Juuti, P., Tuominen, M., Sillanpää, M., Stepien, M., Saarinen, J. J., Toivakka, M., Kuusipalo, J., Mäkelä, J. M.
Publication date: 2019
Peer-reviewed: Yes
Early online date: 5 Dec 2018

Publication information

Journal: Materials Research Express
Volume: 6
Issue number: 3
Article number: 035004
ISSN (Print): 2053-1591
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Biomaterials, Surfaces, Coatings and Films, Polymers and Plastics, Metals and Alloys
Keywords: liquid flame spray, nanocoatings, nanoparticles, superhydrophobic, TiO, titanium dioxide, wetting
Source: Scopus
Source-ID: 85059238010

Research output: Contribution to journalArticleScientificpeer-review

Packet level performance assessment of mmWave backhauling technology for 3GPP NR Systems

Recently standardized millimeter-wave (mmWave) band 3GPP New Radio systems are expected to bring extraordinary rates to the air interface efficiently providing commercial-grade enhanced mobile broadband services in hotspot areas. One of the challenges of such systems is efficient offloading of the data from access points (AP) to the network infrastructure. This task is of special importance for APs installed in remote areas with no transport network available. In this paper, we assess the packet level performance of mmWave technology for cost-efficient backhauling of remote 3GPP NR APs connectivity 'islands'. Using a queuing system with arrival processes of the same priority competing for transmission resources, we assess the aggregated and per-AP packet loss probability as a function environmental conditions, mmWave system specifics, and generated traffic volume. We show that the autocorrelation in aggregated traffic provides a significant impact on service characteristics of mmWave backhaul and needs to be compensated by increasing either emitted power or the number of antenna array elements. The effect of autocorrelation in the per-AP traffic and background traffic from other APs also negatively affects the per-AP packet loss probability. However, the effect is of different magnitude and heavily depends on the load fraction of per-AP traffic in the aggregated traffic stream. The developed model can be used to parameterize mmWave backhaul links as a function of the propagation environment, system design, and traffic conditions.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, Research group: Wireless Communications and Positioning, National Research University Higher School of Economics, St. Petersburg State Polytechnical University
Contributors: Ometov, A., Moltchanov, D., Komarov, M., Volvenko, S. V., Koucheryavy, Y.
Number of pages: 12
Pages: 9860-9871
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Access
Volume: 7
ISSN (Print): 2169-3536
Original language: English
ASJC Scopus subject areas: Computer Science(all), Materials Science(all), Engineering(all)
Keywords: 5G mobile communication, mathematical model, millimeter wave communication, Next generation networking, queueing analysis, wireless communication

Bibliographical note

EXT="Ometov, Aleksandr"
EXT="Komarov, Mikhail"

Source: Scopus
Source-ID: 85061089480

Research output: Contribution to journalArticleScientificpeer-review

Reliability evaluation of wearable radio frequency identification tags: Design and fabrication of a two-part textile antenna

Passive radio frequency identification-based technology is a convincing approach to the achievement of versatile energy- and cost-efficient wireless platforms for future wearable applications. By using two-part antenna structures, the antenna-electronics interconnections can remain non-stressed, which can significantly improve the reliability of the textile-embedded wireless components. In this article, we describe fabrication of two-part stretchable and non-stretchable passive ultra-high frequency radio frequency identification textile tags using electro-textile and embroidered antennas, and test their reliability when immersed as well as under cyclic strain. The results are compared to tags with traditional one-part dipole antennas fabricated from electro-textiles and by embroidery. Based on the results achieved, the initial read ranges of the two-part antenna tags, around 5 m, were only slightly shorter than those of the one-part antenna tags. In addition, the tag with two-part antennas can maintain high performance in a moist environment and during continuous stretching, unlike the one-part antenna tag where the antenna-integrated circuit attachment is under stress.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Wireless Identification and Sensing Systems Research Group
Contributors: Chen, X., Ukkonen, L., Virkki, J.
Publication date: 2019
Peer-reviewed: Yes
Early online date: 1 Jan 2018

Publication information

Journal: Textile Research Journal
Volume: 89
Issue number: 4
ISSN (Print): 0040-5175
Original language: English
ASJC Scopus subject areas: Chemical Engineering (miscellaneous), Polymers and Plastics
Keywords: E-textile antenna, embroidery antenna, radio frequency identification
Source: Scopus
Source-ID: 85045121603

Research output: Contribution to journalArticleScientificpeer-review

Remote diagnostics application software for remote handling equipment

The ITER Remote Handling Control System (RHCS) controllers provide measurement and diagnostics data about the remote handling equipment and tools they control. This paper presents the Remote Diagnostics Application (RDA) software for the analysis and archiving of the RHCS diagnostics data. The RDA provides a basic set of diagnostics tools, including trends, spectra, histograms, scatter plots, cross-correlation plots, as well as archiving and retrieval of history data. The ITER RH operators can extend diagnostics capabilities for specific RH equipment needs by incorporating custom diagnostics functions. To facilitate customization, RDA implements an architecture with three nested levels: the RDA Framework, its Diagnostics Workbenches and their Diagnostics Primitives. The RDA Framework has a user interface that can load one or several special diagnostics cases implemented as custom Diagnostics Workbenches with custom or default Diagnostics Primitives, such as rules, analysis functions and filters. As a result, the RDA features a diagnostics framework to execute complex and dedicated diagnostics and prognostics for the RH experts to monitor performance data, to run diagnostics tests and rules on equipment systems and to analyse historical data. The RDA helps the RH operators reduce downtime of the Remote Handling systems by exposing failure conditions and maintenance needs.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Automation Technology and Mechanical Engineering, VTT Technical Research Centre of Finland, Fusion For Energy (F4E)
Contributors: Alanen, J., Ruiz Morales, E., Muhammad, A., Saarinen, H., Minkkinen, J.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Fusion Engineering and Design
ISSN (Print): 0920-3796
Original language: English
ASJC Scopus subject areas: Civil and Structural Engineering, Nuclear Energy and Engineering, Materials Science(all), Mechanical Engineering
Keywords: Control system, Diagnostics, Prognostics, Remote handling, Software

Bibliographical note

EXT="Saarinen, Hannu"

Source: Scopus
Source-ID: 85060619368

Research output: Contribution to journalArticleScientificpeer-review

Role of Steel Plate Thickness on the Residual Stress Formation and Cracking Behavior During Flame Cutting

Thick wear-resistant steel plates are utilized in challenging applications, which require a high hardness and toughness. However, utilization of the thick plates is problematic as they often have nonuniform mechanical properties along the thickness direction due to the manufacturing-induced segregations. In addition, the processing of thick plates commonly involves flame cutting, which causes several challenges. Flame cutting forms a heat-affected zone and generates high residual stresses during the cutting process. In the worst case, flame cutting causes cracking of the cut edge. The aim of this study is to investigate the role of plate thickness on the residual stress formation and cracking behavior when utilizing flame cutting. Residual stress profiles are measured by X-ray diffraction, plates and cut edges and are mechanically tested and characterized by electron microscopy. The results show that thicker plates generate more unfavorable residual stress state during flame cutting. Thick plates also contain segregations, which have decreased mechanical properties. The combination of high residual tensile stresses and segregations increase the risk of cracking during flame cutting. To prevent the cracking, the residual stresses should be lowered by lower cutting speeds and preheating. In addition, manufacturing practices should be aimed at lowering segregation formation in thick plates.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science and Environmental Engineering
Contributors: Jokiaho, T., Santa-aho, S., Peura, P., Vippola, M.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
ISSN (Print): 1073-5623
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Mechanics of Materials, Metals and Alloys
Source: Scopus
Source-ID: 85068025007

Research output: Contribution to journalArticleScientificpeer-review

Textile-integrated three-dimensional printed and embroidered structures for wearable wireless platforms

In this paper, we present fabrication and performance evaluation of three-dimensional (3D) printed and embroidered textile-integrated passive ultra high frequency radio frequency identification (RFID) platforms. The antennas were manufactured by 3D printing a stretchable silver conductor directly on an elastic band. The electric and mechanical joint between the 3D printed antennas and microchips was formed by gluing with conductive epoxy glue, by printing the antenna directly on top of the microchip structure, and by embroidering with conductive yarn. Initially, all types of fabricated RFID tags achieved read ranges of 8–9 meters. Next, the components were tested for wetting as well as for harsh cyclic strain and bending. The immersing and cyclic bending slightly affected the performance of the tags. However, they did not stop the tags from working in an acceptable way, nor did they have any permanent effect. The epoxy-glued or 3D printed antenna–microchip interconnections were not able to endure harsh stretching. On the other hand, the tags with the embroidered antenna–microchip interconnections showed excellent wireless performance, both during and after a 100 strong stretching cycles. Thus, the novel approach of combining 3D printing and embroidery seems to be a promising way to fabricate textile-integrated wireless platforms.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Wireless Identification and Sensing Systems Research Group
Contributors: He, H., Chen, X., Ukkonen, L., Virkki, J.
Publication date: 2019
Peer-reviewed: Yes
Early online date: 1 Jan 2018

Publication information

Journal: Textile Research Journal
Volume: 89
Issue number: 4
ISSN (Print): 0040-5175
Original language: English
ASJC Scopus subject areas: Chemical Engineering (miscellaneous), Polymers and Plastics
Keywords: antennas, embroidery, interconnections, passive ultra high frequency radio frequency identification, stretchable electronics, textile-integrated electronics, three-dimensional printing, wearable platforms
Source: Scopus
Source-ID: 85045101109

Research output: Contribution to journalArticleScientificpeer-review

Validation of Printed, Skin-Mounted Multilead Electrode for ECG Measurements

An electrocardiography (ECG) monitoring can be used to detect heart-related abnormalities by recording cardiac activity over a period of time. The conventional 12-lead ECG measurement system is the standard practice for the evaluation of the heart's electrical activity. However, a recent trend is to develop patch-type measurement devices for unobtrusive ECG monitoring by reducing device size and number of electrodes on the skin. This development aims to minimize the discomfort for the user from the wearable recording devices. A printed, bandage-type hybrid system for continuous ECG monitoring to allow as much comfort as possible while maintaining the signal quality required for medical evaluation is proposed. Movement artifacts in recorded ECG signals are a challenge in long-term monitoring while the patients are engaged in their everyday activities. The movement artifacts from the printed skin-conformable electrode are compared to commercial exercise stress-test ECG electrodes during different physical activities and stationary periods. The results show that the signal quality obtained with the multilead patch ECG electrode, manufactured with printing technologies, is comparable to electrodes currently used in healthcare.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, BioMediTech, Univ of Oulu, Tampere University, Tampere Uni. of Applied Sci.
Contributors: Vuorinen, T., Noponen, K., Vehkaoja, A., Onnia, T., Laakso, E., Leppänen, S., Mansikkamäki, K., Seppänen, T., Mäntysalo, M.
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Advanced Materials Technologies
Article number: 1900246
ISSN (Print): 2365-709X
Original language: English
ASJC Scopus subject areas: Materials Science(all), Mechanics of Materials, Industrial and Manufacturing Engineering
Keywords: electrocardiography, epidermal electronics, screen printing, stretchable electronics
Source: Scopus
Source-ID: 85067471725

Research output: Contribution to journalArticleScientificpeer-review

Vocal Effort Based Speaking Style Conversion Using Vocoder Features and Parallel Learning

Speaking style conversion (SSC) is the technology of converting natural speech signals from one style to another. In this study, we aim to provide a general SSC system for converting styles with varying vocal effort and focus on normal-to-Lombard conversion as a case study of this problem. We propose a parametric approach that uses a vocoder to extract speech features. These features are mapped using parallel machine learning models from utterances spoken in normal style to the corresponding features of Lombard speech. Finally, the mapped features are converted to a Lombard speech waveform with the vocoder. A total of three vocoders (GlottDNN, STRAIGHT, and Pulse model in log domain (PML)) and three machine learning mapping methods (standard GMM, Bayesian GMM, and feed-forward DNN) were compared in the proposed normal-to-Lombard style conversion system. The conversion was evaluated using two subjective listening tests measuring perceived Lombardness and quality of the converted speech signals, and by using an instrumental measure called Speech Intelligibility in Bits (SIIB) for speech intelligibility evaluation under various noise levels. The results of the subjective tests show that the system is able to convert normal speech into Lombard speech and that there is a trade-off between quality and Lombardness of the mapped utterances. The GlottDNN and PML stand out as the best vocoders in terms of quality and Lombardness, respectively, whereas the DNN is the best mapping method in terms of Lombardness. PML with the standard GMM seems to give a good compromise between the two attributes. The SIIB experiments indicate that intelligibility of converted speech compared to that of normal speech improved in noisy conditions most effectively when DNN mapping was used with STRAIGHT and PML.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, Aalto University
Contributors: Seshadri, S., Juvela, L., Räsänen, O., Alku, P.
Number of pages: 17
Pages: 17230-17246
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Access
Volume: 7
ISSN (Print): 2169-3536
Original language: English
ASJC Scopus subject areas: Computer Science(all), Materials Science(all), Engineering(all)
Keywords: Bayesian GMM, DNN, GlottDNN, Lombard speech, pulse model in log domain, speaking style conversion, vocal effort
Source: Scopus
Source-ID: 85061789099

Research output: Contribution to journalArticleScientificpeer-review

Oxidation-Induced Changes in the ALD-Al2O3/InAs(100) Interface and Control of the Changes for Device Processing

InAs crystals are emerging materials for various devices like radio frequency transistors and infrared sensors. Control of oxidation-induced changes is essential for decreasing amounts of the harmful InAs surface (or interface) defects because it is hard to avoid the energetically favored oxidation of InAs surface parts in device processing. We have characterized atomic-layer-deposition (ALD) grown Al2O3/InAs interfaces, preoxidized differently, with synchrotron hard X-ray photoelectron spectroscopy (HAXPES), low-energy electron diffraction, scanning tunneling microscopy, and time-of-flight elastic recoil detection analysis. The chemical environment and core-level shifts are clarified for well-embedded InAs interfaces (12 nm Al2O3) to avoid, in particular, effects of a significant potential change at the vacuum-solid interface. High-resolution As 3d spectra reveal that the Al2O3/InAs interface, which was sputter-cleaned before ALD, includes +1.0 eV shift, whereas As 3d of the preoxidized (3 × 1)-O interface exhibits a shift of -0.51 eV. The measurements also indicate that an As2O3 type structure is not crucial in controlling defect densities. Regarding In 4d measurements, the sputtered InAs interface includes only a +0.29 eV shift, while the In 4d shift around -0.3 eV is found to be inherent for the crystalline oxidized interfaces. Thus, the negative shifts, which have been usually associated with dangling bonds, are not necessarily an indication of such point defects as previously expected. In contrast, the negative shifts can arise from bonding with O atoms. Therefore, specific care should be directed in determining the bulk-component positions in photoelectron studies. Finally, we present an approach to transfer the InAs oxidation results to a device process of high electron mobility transistors (HEMT) using an As-rich III-V surface and In deposition. The approach is found to decrease a gate leakage current of HEMT without losing the gate controllability.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Department of Physics and Astronomy, University of Turku, University of Turku, Soft Matter and Functional Materials, Helmholtz-Zentrum Berlin, University of Jyvaskyla
Contributors: Tuominen, M., Mäkelä, J., Yasir, M., Dahl, J., Granroth, S., Lehtiö, J. P., Félix, R., Laukkanen, P., Kuzmin, M., Laitinen, M., Punkkinen, M. P., Hedman, H. P., Punkkinen, R., Polojärvi, V., Lyytikäinen, J., Tukiainen, A., Guina, M., Kokko, K.
Number of pages: 9
Pages: 44932-44940
Publication date: 26 Dec 2018
Peer-reviewed: Yes

Publication information

Journal: ACS Applied Materials and Interfaces
Volume: 10
Issue number: 51
ISSN (Print): 1944-8244
Ratings: 
  • Scopus rating (2018): CiteScore 8.69 SJR 2.596 SNIP 1.539
Original language: English
ASJC Scopus subject areas: Materials Science(all)
Keywords: atomic layer deposition, III-V semiconductor, InAs, oxidation, photoelectron, synchrotron

Bibliographical note

EXT="Mäkelä, Jaakko"
EXT="Kuzmin, Mikhail"
EXT="Laukkanen, Pekka"

Source: Scopus
Source-ID: 85059448335

Research output: Contribution to journalArticleScientificpeer-review

Reversible photodoping of TiO2 nanoparticles

Observations on strong photochromic effect of crystalline TiO2 quantum dots (mean size ≈ 4 nm) are presented. The synthesized quantum dots consist of irregularly shaped anatase TiO2 nanoparticles (NPs) and are dispersed in butanol (8 % by mass). Obtained NPs exhibit a dramatic photo-response to UV light, enabling effective transmittance modula-tion of in a broad wavelength range extending from visible to near-infrared region, and even the thermal black body radiation regime beyond 10 μm. The exceptional photo-response is attributed to hole-scavenging by butanol, TiO2 self-reduction, injection of electrons to the conduction band, and consequent localized surface plasmon resonances in NPs. Observed optical effect is reversible and the initial high transmittance state can be restored simply by exposing the NPs to air. Applied NP synthesis route is economic and can be easily scaled for applications such as smart window technol-ogies.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Surface Science, Univ Tartu, University of Tartu, University of Tartu Institute of Physics, Inst Phys, University of Tartu
Contributors: Joost, U., Sutka, A., Oja, M., Smits, K., Doebelin, N., Loot, A., Järvekülg, M., Hirsimäki, M., Valden, M., Nommiste, E.
Pages: 8968-8974
Publication date: 26 Dec 2018
Peer-reviewed: Yes
Early online date: 10 Dec 2018

Publication information

Journal: Chemistry of Materials
Volume: 30
Issue number: 24
ISSN (Print): 0897-4756
Ratings: 
  • Scopus rating (2018): CiteScore 9.92 SJR 4.224 SNIP 1.769
Original language: English
ASJC Scopus subject areas: Inorganic Chemistry, Materials Chemistry, Surfaces and Interfaces, Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Keywords: tio2, nano, nanoparticle, photochromic, anatase, light, photonics, functional
URLs: 

Bibliographical note

INT=fot,"Joost, Urmas"

Research output: Contribution to journalArticleScientificpeer-review

Less Is More: Enhancement of Second-Harmonic Generation from Metasurfaces by Reduced Nanoparticle Density

We investigate optical second-harmonic generation (SHG) from metasurfaces where noncentrosymmetric V-shaped gold nanoparticles are ordered into regular array configurations. In contrast to expectations, a substantial enhancement of the SHG signal is observed when the number density of the particles in the array is reduced. More specifically, by halving the number density, we obtain over 5-fold enhancement in SHG intensity. This striking result is attributed to favorable interparticle interactions mediated by the lattice, where surface-lattice resonances lead to spectral narrowing of the plasmon resonances. Importantly, however, the results cannot be explained by the improved quality of the plasmon resonance alone. Instead, the lattice interactions also lead to further enhancement of the local fields at the particles. The experimental observations agree very well with results obtained from numerical simulations including lattice interactions.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Institute of Physics, Nicolaus Copernicus University, University of Eastern Finland, CRPP
Contributors: Czaplicki, R., Kiviniemi, A., Huttunen, M. J., Zang, X., Stolt, T., Vartiainen, I., Butet, J., Kuittinen, M., Martin, O. J., Kauranen, M.
Number of pages: 6
Pages: 7709-7714
Publication date: 12 Dec 2018
Peer-reviewed: Yes

Publication information

Journal: Nano Letters
Volume: 18
Issue number: 12
ISSN (Print): 1530-6984
Ratings: 
  • Scopus rating (2018): CiteScore 12.71 SJR 6.211 SNIP 2.396
Original language: English
ASJC Scopus subject areas: Bioengineering, Chemistry(all), Materials Science(all), Condensed Matter Physics, Mechanical Engineering
Keywords: interparticle interactions, Metal nanoparticles, nonlinear optics, plasmonic resonances, second-harmonic generation, surface-lattice resonances
Additional files: 
URLs: 
Source: Scopus
Source-ID: 85058303843

Research output: Contribution to journalArticleScientificpeer-review

Experimental moment resistance of rectangular hollow section T joints

Resistance is the main property of tubular joints. The determination of the joint resistance from the experimental load-deformation curve always represents a challenging task. Currently there are two main methods to find the experimental resistance, which are called plastic and ultimate resistance. However, there is no single opinion on which one should be commonly used. Based on the experimental results, this paper directly compares the two existed approaches. The study is restricted to welded square hollow section T joints under in-plane bending moment. The paper considers only the joints with β < 0.85, i.e. when the behaviour of the joint is governed by chord face failure. The results show that plastic resistance leads to more conservative results than ultimate resistance, providing thus safer results. However, attention should be also paid to the difference between the labour intensity of the presented methods.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Civil Engineering
Contributors: Garifullin, M.
Publication date: 5 Dec 2018
Peer-reviewed: Yes

Publication information

Journal: MATEC Web of Conferences
Volume: 245
Article number: 08003
ISSN (Print): 2274-7214
Ratings: 
  • Scopus rating (2018): CiteScore 0.42 SJR 0.169 SNIP 0.548
Original language: English
ASJC Scopus subject areas: Chemistry(all), Materials Science(all), Engineering(all)
Electronic versions: 
Source: Scopus
Source-ID: 85058463414

Research output: Contribution to journalConference articleScientificpeer-review

Considerations in analysing elemental carbon from marine engine exhaust using residual, distillate and biofuels

Elemental carbon (EC) concentrations in the exhaust of a medium-speed marine engine was evaluated using thermal-optical analysis (TOA). Particulate matter (PM) samples were collected at 75% and 25% engine loads using residual and distillate fuels with sulphur contents of 2.5%, 0.5% and 0.1%, and a biofuel (30% of bio-component). The EC analysis of PM samples from a marine engine proved to be challenging. For example, transformations of structure of the sampled particles in the inert and the oxygen mode were observed for marine engine exhaust samples. The relationship between constituents present in the samples from the marine engine using different fuels, and phenomena observed in the thermograms are discussed. Temperature protocol selection and sample pre-treatment (extractions and drying) affected the reported EC mass. Modifications in the methodology were suggested to increase the accuracy of the analysis. Repeatability and reproducibility of the EC analysis was studied in the round-robin of three laboratories.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: The Instrumentation, Emissions, and Atmospheric Aerosols Group, Research area: Aerosol Physics, VTT Technical Research Centre of Finland, Finnish Meteorological Institute, University of Eastern Finland, Public Health Service (GGD) Amsterdam
Contributors: Aakko-Saksa, P., Koponen, P., Aurela, M., Vesala, H., Piimäkorpi, P., Murtonen, T., Sippula, O., Koponen, H., Karjalainen, P., Kuittinen, N., Panteliadis, P., Rönkkö, T., Timonen, H.
Number of pages: 14
Pages: 191-204
Publication date: Dec 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Aerosol Science
Volume: 126
ISSN (Print): 0021-8502
Ratings: 
  • Scopus rating (2018): CiteScore 2.33 SJR 0.696 SNIP 1.039
Original language: English
ASJC Scopus subject areas: Environmental Chemistry, Materials Science(all), Pollution
Keywords: Elemental carbon EC, Fuel, Marine engine, Round-robin, Thermal-optical analysis TOA, Thermogram
Source: Scopus
Source-ID: 85054296019

Research output: Contribution to journalArticleScientificpeer-review

Effects of Microstructure on the Dynamic Strain Aging in Ferritic-Pearlitic Steels

Effects of microstructure on the high strain rate high temperature mechanical response and dynamic strain aging of C45 and 27MnCr5 ferritic-pearlitic steels were studied using four different microstructural variants of the standard alloys. The high strain rate high temperature behavior of the steels was studied using a compression Split Hopkinson Pressure Bar device with high temperature testing capabilities. The steels were studied at strain rates up to 4500 s−1 and at temperatures from RT to 680 °C. Strong dynamic strain aging was observed for both steels in the studied temperature range. The results also show that the microstructure has a strong effect on the dynamic strain aging sensitivity of the steel. This is especially true at low plastic strains, where the effect of the microstructure is strongest. The effect of microstructure decreases as plastic strain increases. A coarse-grained microstructure showed the strongest dynamic strain aging sensitivity for both steels.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Swerea KIMAB AB, Schmolz+Bichenbach Group CREAS
Contributors: Hokka, M., Rämö, J., Mardoukhi, A., Vuoristo, T., Roth, A., Kuokkala, V. T.
Pages: 452-463
Publication date: Dec 2018
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Journal of Dynamic Behavior of Materials
Volume: 4
Issue number: 4
ISSN (Print): 2199-7446
Ratings: 
  • Scopus rating (2018): CiteScore 2.16 SJR 0.653 SNIP 1.573
Original language: English
ASJC Scopus subject areas: Materials Science (miscellaneous), Mechanics of Materials
Keywords: Dynamic strain aging, Effects of microstructure, High strain rate, High temperature, Steels
Source: Scopus
Source-ID: 85051680227

Research output: Contribution to journalArticleScientificpeer-review

ICED - Inductively Coupled Energy Dissipater for Future High Field Accelerator Magnets

Future high field accelerator magnets, like the ones foreseen in the design study of the FCC project and for the EuCARD2 "Future Magnets" program, operate with magnetic fields in the range of 16<formula><tex>$\times$</tex></formula>20T. For such magnets the energy density is higher than in the accelerator magnets at present in operation, posing a challenge for the quench protection. Traditionally quench protection has relied on generating large normal zones in the coil by firing quench protection heaters. The increase of the coil internal resistance results in a fast current decay. This paper introduces the Inductively Coupled Energy Dissipater (ICED) system, based on low resistance loops which are inductively coupled with the coil. These loops greatly accelerate the current decay by rapidly extracting the energy from the coil, thereby lowering its peak temperature. Because of the potential reduction in stabilizer volume within the conductor, ICED may enable higher engineering current densities in the coil than with the protection relying entirely on dissipating the magnet's energy in the windings. The efficiency of ICED as a passive quench protection system is studied in this paper. We present the effect of such protection structure on the field quality during standard powering of the magnets and on the cryogenic system. We study electromagnetic forces in the loops and mechanically stable geometric locations within the magnet structure. For the proof of the concept, this system has been employed in Feather-M2 dipole demonstrator. We compare our modeling approach to results gained from a cryogenic test.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, European Organization for Nuclear Research
Contributors: Murtomäki, J. S., van Nugteren, J., Kirby, G., DeRijk, G., Rossi, L., Stenvall, A.
Publication date: Dec 2018
Peer-reviewed: Yes
Early online date: 28 May 2018

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 28
Issue number: 8
Article number:  4009015
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2018): CiteScore 1.65 SJR 0.406 SNIP 0.969
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Accelerator magnets, Electromagnetic Induction, Heating systems, High-temperature superconductors, High-Temperature-Superconductors, Magnetomechanical effects, Resistance, Superconducting magnets, Superconducting Magnets, Windings
Source: Scopus
Source-ID: 85047834232

Research output: Contribution to journalArticleScientificpeer-review

Cell response to round and star-shaped polylactide fibers

The surface topography of tissue engineering biomaterials is known to affect cell behavior. Polymer fibers can be processed into a variety of diameters and shapes, which both affect the orientation and organization of cells. The fibers can be used to manufacture tissue engineering scaffolds. The aim of this work was to study cell response to microfibers with round and star-shaped cross-sections. In addition, the retention of fiber properties during hydrolytic degradation was evaluated.

Melt spinning method was used to process poly-L/D-lactide 96/4 (PLDLA 96/4) fibers. Knitted scaffolds were manufactured from the fibers for the cell culture experiment. A hydrolytic degradation experiment was conducted for the fibers to evaluate retention of mechanical properties and changes in crystallinity and thermal properties. Human urothelial cells (hUCs) and human foreskin fibroblasts (hFFs) were used in the cell culture experiment. Cell response was assessed using live/dead analysis and crystal violet staining.

Both fibers had suitable mechanical properties to be processed into knitted scaffolds. The hydrolytic degradation experiment demonstrated good retention of properties for the fibers. The number of cells attached to the fibers increased throughout the experiment. The hFFs oriented to the fiber direction on both fibers. The cell culture experiment demonstrated good biocompatibility and no observable difference in cell response was seen between the fiber types.

General information

Publication status: Published
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Biomaterials and Tissue Engineering Group, University of Tampere, Faculty of Medicine and Life Sciences, Lääkärinkatu 1, 33520 Tampere, Finland, Adult Stem Cell Research Group
Contributors: Kroon, M., Talvitie, E., Miettinen, S., Kellomäki, M.
Publication date: 23 Nov 2018
Peer-reviewed: Unknown
Event: Paper presented at BioMediTech Research Day 2018, Tampere, Finland.
ASJC Scopus subject areas: Biomaterials
Keywords: Polylactide, Tissue Engineering, Cell Culture, Scaffolds, Biotextiles

Research output: Other conference contributionPaper, poster or abstractScientific

Cascaded crystalline raman lasers for extended wavelength coverage: Continuous-wave, third-stokes operation

The development of high-power laser sources with narrow emission, tunable within the water transmission window around 1.7 μm, is of interest for applications as diverse as medical imaging and atmospheric sensing. Where suitable laser gain media are not available, operation in this spectral region is often achieved via nonlinear frequency conversion, and optical parametric oscillators (OPOs) are a common solution. A practical alternative to OPOs, to avoid birefringent-or quasi-phase-matching requirements, is the use of stimulated Raman scattering within a suitable material to convert a pump source to longer wavelengths via one or more Stokes shifts; however, as this is a χ3 nonlinear process, such frequency conversion is usually the preserve of high-energy pulsed lasers. Semiconductor disk lasers (SDLs), on the other hand, have very high-finesse external resonators, suitable for efficient intracavity nonlinear conversion even in continuous-wave (CW) operation. Here we report, to the best of our knowledge, the first continuous-wave third-Stokes crystalline Raman laser and the longest emission wavelength from an SDL-pumped Raman laser, achieving high power, CW output, and broad wavelength tuning around 1.73 μm. The KGd WO4 2 (KGW) Raman laser, which was intracavity-pumped by a 1.18 μm InGaAs-based SDL, demonstrated cascaded CW Stokes oscillation at 1.32 μm, 1.50 μm, and 1.73 μm with watt-level output achievable at each wavelength. The 1.73 μm Stokes emission was diffraction limited (M2 < 1.01) and narrow linewidth (<46 pm FWHM; measurement limited). By rotation of a birefringent filter placed within the fundamental resonator, we attained three tunable emission wavelength bands, one centred at each Stokes component, and achieved up to 65 nm tuning for the third-Stokes Raman laser from 1696 nm to 1761 nm. We have thus demonstrated a platform laser technology that takes well-developed InGaAs-based SDLs and provides spectral coverage and high performance in the near-infrared water transmission windows using commercially available components.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, University of Strathclyde
Contributors: Casula, R., Penttinen, J., Guina, M., Kemp, A. J., Hastie, J. E.
Number of pages: 8
Pages: 1406-1413
Publication date: 20 Nov 2018
Peer-reviewed: Yes

Publication information

Journal: Optica
Volume: 5
Issue number: 11
ISSN (Print): 2334-2536
Ratings: 
  • Scopus rating (2018): CiteScore 10.26 SJR 4.914 SNIP 3.088
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Source: Scopus
Source-ID: 85059018872

Research output: Contribution to journalArticleScientificpeer-review

Optical properties of GaAs1-xBix/GaAs quantum well structures grown by molecular beam epitaxy on (100) and (311)B GaAs substrates

In this work, the electronic bandstructure of GaAs1-xBix/GaAs single quantum well (QW) samples grown by molecular beam epitaxy is investigated by photomodulated reflectance (PR) measurements as a function of Bi content (0.0065 ≤ x ≤ 0.0215) and substrate orientation. The Bi composition is determined via simulation of high-resolution x-ray diffraction measurement and is found to be maximized in the 2.15%Bi and 2.1%Bi samples grown on (100) and (311)B GaAs substrates. However, the simulations indicate that the Bi composition is not only limited in the GaAsBi QW layer but extends out of the GaAsBi QW towards the GaAs barrier and forms a GaAsBi epilayer. PR spectra are fitted with the third derivative function form (TDFF) to identify the optical transition energies. We analyze the TDFF results by considering strain-induced modification on the conduction band (CB) and splitting of the valence band (VB) due to its interaction with the localized Bi level and VB interaction. The PR measurements confirm the existence of a GaAsBi epilayer via observed optical transitions that belong to GaAsBi layers with various Bi compositions. It is found that both Bi composition and substrate orientation have strong effects on the PR signal. Comparison between TDFF and calculated optical transition energies provides a bandgap reduction of 92 meV/%Bi and 36 meV/%Bi and an interaction strength of the isolated Bi atoms with host GaAs valence band (C BiM ) of 1.7 eV and 0.9 eV for (100) and (311)B GaAs substrates, respectively.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC, Adana Science and Technology University, Istanbul University, University of Cukurova, University of Nottingham, Universidade Federal de São Carlos, Leibniz Institute for Crystal Growth
Contributors: Gunes, M., Ukelge, M. O., Donmez, O., Erol, A., Gumus, C., Alghamdi, H., Galeti, H. V., Henini, M., Schmidbauer, M., Hilska, J., Puustinen, J., Guina, M.
Publication date: 13 Nov 2018
Peer-reviewed: Yes

Publication information

Journal: Semiconductor Science and Technology
Volume: 33
Issue number: 12
Article number: 124015
ISSN (Print): 0268-1242
Ratings: 
  • Scopus rating (2018): CiteScore 2.4 SJR 0.744 SNIP 1.002
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering, Materials Chemistry
Keywords: high-index substrate, oriented GaAsBi, photomodulated reflectance, strained quantum well, type I band line-up
Source: Scopus
Source-ID: 85057810892

Research output: Contribution to journalArticleScientificpeer-review

Tunable Reflection Type Plasmon Induced Transparency with Graphene

Plasmon induced transparency (PIT) has always been investigated in transmission mode, which makes the design dependent upon the type of substrate. In this work, we propose a first tunable reflection type PIT (RPIT) device based on simple design of two parallel gold strips on graphene. We have numerically investigated the design by using Finite Difference Time-Domain (FDTD) method. This response is tunable by changing the Fermi level (Ef) of graphene. High tunability of 215 nm shift was observed by changing the Ef of graphene from 0 to 0.8 eV. The spectral contrast ratio of our device is 99.2%.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Photonics, Department of Electrical and Electronics Engineering, Bilkent University, Nanotechnology Research Center
Contributors: Habib, M., Ozbay, E., Caglayan, H.
Number of pages: 3
Pages: 170-172
Publication date: 13 Nov 2018

Host publication information

Title of host publication: 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena, METAMATERIALS 2018
Publisher: IEEE
ISBN (Electronic): 9781538647028
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Acoustics and Ultrasonics, Atomic and Molecular Physics, and Optics, Radiation

Bibliographical note

EXT="Habib, M."

Source: Scopus
Source-ID: 85058538366

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Enhanced multiaxial fatigue criterion that considers stress gradient effects

Modification of a fatigue criterion valid for homogeneous multiaxial stress states to account for the beneficial effect of stress gradients is traditionally performed by modifying the stress terms in the fatigue criterion and thereby introducing new parameters that need to be calibrated. Here the stress terms are left unchanged and, instead, the parameters in the fatigue criterion are modified. This modification is performed, in principle, along the lines of Siebel and Stieler and it introduces Neuber's parameter as the only new parameter; however, as soon as the ultimate strength of the material is known, also Neuber's parameter is known. Therefore, the methodology introduced implies that no new calibration process is needed. Here a specific fatigue criterion valid for homogeneous multiaxial stress states is enhanced by this procedure and predictions of this simple approach are compared with a broad range of experimental data and good accuracy is achieved. Moreover, the approach adopted can be applied to other fatigue criteria than the one considered here.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Civil Engineering, Lund University
Contributors: Ottosen, N. S., Ristinmaa, M., Kouhia, R.
Number of pages: 12
Pages: 128-139
Publication date: 1 Nov 2018
Peer-reviewed: Yes

Publication information

Journal: International Journal of Fatigue
Volume: 116
ISSN (Print): 0142-1123
Ratings: 
  • Scopus rating (2018): CiteScore 4.21 SJR 2.059 SNIP 2.412
Original language: English
ASJC Scopus subject areas: Modelling and Simulation, Materials Science(all), Mechanics of Materials, Mechanical Engineering, Industrial and Manufacturing Engineering
Keywords: Fatigue, Gradient effects, Multiaxial fatigue
Source: Scopus
Source-ID: 85048733879

Research output: Contribution to journalArticleScientificpeer-review

Tribocorrosion behaviour of aluminium bronze in 3.5 wt.% NaCl solution

Tribocorrosion behaviour of aluminium bronze CuAl10Fe5Ni5 in 3.5 wt.% NaCl solution was investigated in a pin-on-disc facility containing an electrochemical cell. Oxidising capacity and contact pressure to alumina counterbody were varied. Pure corrosion occurred as selective dissolution of α phase included in the eutectoid structure. Contact to counterbody introduced plastic deformation, extrusion of the material and abrasive wear. Wear-corrosion interactions varied between the two contact pressures, with lower material losses appearing at the higher pressure. The significant acceleration of material degradation by the interactions was not clearly reflected to kinetics or thermodynamics of corrosion. These results are presented and discussed here.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, VTT Technical Research Centre of Finland
Contributors: Huttunen-Saarivirta, E., Isotahdon, E., Metsäjoki, J., Salminen, T., Carpén, L., Ronkainen, H.
Number of pages: 17
Pages: 207-223
Publication date: 1 Nov 2018
Peer-reviewed: Yes

Publication information

Journal: Corrosion Science
Volume: 144
ISSN (Print): 0010-938X
Ratings: 
  • Scopus rating (2018): CiteScore 6.76 SJR 2.131 SNIP 2.595
Original language: English
ASJC Scopus subject areas: Chemistry(all), Chemical Engineering(all), Materials Science(all)
Keywords: Corrosion, Plastic deformation, Selective dissolution, Tribocorrosion, Wear

Bibliographical note

EXT="Huttunen-Saarivirta, E."
EXT="Isotahdon, E."
EXT="Metsäjoki, J."

Source: Scopus
Source-ID: 85053038794

Research output: Contribution to journalArticleScientificpeer-review

Sensitivity Analysis of Inverse Thermal Modeling to Determine Power Losses in Electrical Machines

Inverse analysis is a known mathematical approach, which has been used to solve physical problems of a particular nature. Nevertheless, it has seldom been applied directly for loss reconstruction of electrical machines. This paper aims to verify the accuracy of an inverse methodology used in mapping power loss distribution in an induction motor. Conjugate gradient method is used to iteratively find the unique inverse solution when simulated temperature measurement data are available. Realistic measurement situations are considered and the measurement errors corresponding to thermographic measurements and temperature sensor measurements are used to generate simulated numerical measurement data. An accurate 2-D finite-element thermal model of a 37 kW cage induction motor serves as the forward solution. The inverse model's objective is to map the power loss density in the motor accurately from noisy temperature measurements made on the motor housing's outer surface. Furthermore, the sensitivity of the adopted inverse methodology to variations in the number of available measurements is also considered. Filtering the applied noise to acceptable ranges is shown to improve the inverse mapping results.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, Aalto University
Contributors: Nair, D. G., Rasilo, P., Arkkio, A.
Publication date: Nov 2018
Peer-reviewed: Yes
Early online date: 23 Jul 2018

Publication information

Journal: IEEE Transactions on Magnetics
Volume: 54
Issue number: 11
Article number: 8109405
ISSN (Print): 0018-9464
Ratings: 
  • Scopus rating (2018): CiteScore 1.71 SJR 0.539 SNIP 0.996
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering
Keywords: Heat transfer, Heating systems, induction motor, Induction motors, inverse problems, Loss measurement, Noise measurement, Stator windings, Temperature measurement
Electronic versions: 
Source: Scopus
Source-ID: 85050587914

Research output: Contribution to journalArticleScientificpeer-review

An efficient highly flexible strain sensor: Enhanced electrical conductivity, piezoresistivity and flexibility of a strongly piezoresistive composite based on conductive carbon black and an ionic liquid

Flexible strain sensors based on conductive carbon black (CB) filled styrene-butadiene rubber were developed. The use of ionic liquid (IL) allows improvement of the filler dispersion, rubber-filler interaction and flexibility of the sample that finally enhances the piezoresistive performance and the sensibility. At filler loading close to the percolation threshold, the electrical conductivity increases by two orders of magnitude when the IL/CB ratio is increased from 0 to 1.5. In contrast to the use of normal plasticisers, the loss in piezoresistivity at low strains is overcome. The sensitivity at 2.5% strain using an IL/CB ratio of 1.5 is about 600% higher compared with the sample without IL. Also, the response consistency becomes better with higher IL/CB ratios. Moreover, the use of IL allows the composites to be deformed more easily while still providing high responsivity to small strains. This enables the construction of better flexible strain sensors with long-term stability.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Mahidol University, Leibniz-Institut für Polymerforschung Dresden E.V., Vodafone Department of Mobile Communications Systems, Mahidol University
Contributors: Narongthong, J., Das, A., Le, H. H., Wießner, S., Sirisinha, C.
Number of pages: 9
Pages: 330-338
Publication date: 1 Oct 2018
Peer-reviewed: Yes

Publication information

Journal: Composites Part A: Applied Science and Manufacturing
Volume: 113
ISSN (Print): 1359-835X
Ratings: 
  • Scopus rating (2018): CiteScore 6.9 SJR 1.907 SNIP 2.592
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Mechanics of Materials
Keywords: A. Polymer-matrix composites (PMCs), B. Electrical properties, B. Mechanical properties, Piezoresistivity
Source: Scopus
Source-ID: 85051249560

Research output: Contribution to journalArticleScientificpeer-review

Demonstration of optical nonlinearity in InGaAsP/InP passive waveguides

We report on the study of the third-order nonlinear optical interactions in InxGa1-xAsyP1-y/InP strip-loaded waveguides. The material composition and waveguide structures were optimized for enhanced nonlinear optical interactions. We performed self-phase modulation, four-wave mixing and nonlinear absorption measurements at the pump wavelength 1568 nm in our waveguides. The nonlinear phase shift of up to 2.5π has been observed in self-phase modulation experiments. The measured value of the two-photon absorption coefficient α2 was 19 cm/GW. The four-wave mixing conversion range, representing the wavelength difference between maximally separated signal and idler spectral components, was observed to be 45 nm. Our results indicate that InGaAsP has a high potential as a material platform for nonlinear photonic devices, provided that the operation wavelength range outside the two-photon absorption window is selected.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, University of Ottawa, Canada, Middle East Technical Univ.
Contributors: Saeidi, S., Rasekh, P., Awan, K. M., Tüğen, A., Huttunen, M. J., Dolgaleva, K.
Number of pages: 7
Pages: 524-530
Publication date: 1 Oct 2018
Peer-reviewed: Yes

Publication information

Journal: Optical Materials
Volume: 84
ISSN (Print): 0925-3467
Ratings: 
  • Scopus rating (2018): CiteScore 2.6 SJR 0.59 SNIP 1.009
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Computer Science(all), Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: Integrated optics, Nonlinear optics, Optical devices
Source: Scopus
Source-ID: 85050358317

Research output: Contribution to journalArticleScientificpeer-review

Novel osteoconductive β-tricalcium phosphate/poly(L-lactide-co-e-caprolactone) scaffold for bone regeneration: a study in a rabbit calvarial defect

The advantages of synthetic bone graft substitutes over autogenous bone grafts include abundant graft volume, lack of complications related to the graft harvesting, and shorter operation and recovery times for the patient. We studied a new synthetic supercritical CO2 –processed porous composite scaffold of β-tricalcium phosphate and poly(L-lactide-co-caprolactone) copolymer as a bone graft substitute in a rabbit calvarial defect. Bilateral 12 mm diameter critical size calvarial defects were successfully created in 18 rabbits. The right defect was filled with a scaffold moistened with bone marrow aspirate, and the other was an empty control. The material was assessed for applicability during surgery. The follow-up times were 4, 12, and 24 weeks. Radiographic and micro-CT studies and histopathological analysis were used to evaluate new bone formation, tissue ingrowth, and biocompatibility. The scaffold was easy to shape and handle during the surgery, and the bone-scaffold contact was tight when visually evaluated after the implantation. The material showed good biocompatibility and its porosity enabled rapid invasion of vasculature and full thickness mesenchymal tissue ingrowth already at four weeks. By 24 weeks, full thickness bone ingrowth within the scaffold and along the dura was generally seen. In contrast, the empty defect had only a thin layer of new bone at 24 weeks. The radiodensity of the material was similar to the density of the intact bone. In conclusion, the new porous scaffold material, composed of microgranular β-TCP bound into the polymer matrix, proved to be a promising osteoconductive bone graft substitute with excellent handling properties. [Figure not available: see fulltext.].

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electronics and Communications Engineering, Faculty of Biomedical Sciences and Engineering, Research group: Computational Biophysics and Imaging Group, Faculty of Veterinary Medicine, University of Helsinki, Orton Orthopaedic Hospital, Muonio Health Center
Contributors: Pihlman, H., Keränen, P., Paakinaho, K., Linden, J., Hannula, M., Manninen, I. K., Hyttinen, J., Manninen, M., Laitinen-Vapaavuori, O.
Publication date: 1 Oct 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Materials Science: Materials in Medicine
Volume: 29
Issue number: 10
Article number: 156
ISSN (Print): 0957-4530
Ratings: 
  • Scopus rating (2018): CiteScore 2.51 SJR 0.612 SNIP 0.824
Original language: English
ASJC Scopus subject areas: Biophysics, Bioengineering, Biomaterials, Biomedical Engineering
Source: Scopus
Source-ID: 85054473480

Research output: Contribution to journalArticleScientificpeer-review

Solvothermal synthesis derived Co-Ga codoped ZnO diluted magnetic degenerated semiconductor nanocrystals

Here we are reporting solvothermal synthesis derived diluted magnetic and plasmonic Co-Ga co-doped ZnO nanocrystals with high magnetization values (from 1.02 to 4.88 emu/g) at room temperature. Co-Ga co-doped ZnO nanocrystals show up to 2 fold increase in saturation magnetization compared to Co doped ZnO nanocrystals at the same Co concentration, with the observed room temperature magnetization higher than previously reported values for multifunctional magnetic and plasmonic nanocrystals, and the effect of Ga suggesting some role of the correspondingly introduced itinerant charge. While at the lowest Ga content the nanoparticles appear homogeneously doped, we note that already a moderate Ga content of several percent triggers a fraction of Co to segregate in metallic form in the bulk of the nanoparticles. However, the amount of segregated Co is not sufficient to account for the total effect, whereas a dominating contribution to the observed magnetism has to be related to itinerant charge mediated exchange interactions.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Institute of Physics, University of Tartu, Riga Technical University, University of Turku, Helmholtz Centre Berlin for Materials and Energy, University of Latvia, RMS Foundation, Institute of Solid State Physics University of Latvia
Contributors: Šutka, A., Käämbre, T., Joost, U., Kooser, K., Kook, M., Duarte, R. F., Kisand, V., Maiorov, M., Döbelin, N., Smits, K.
Number of pages: 9
Pages: 164-172
Publication date: 30 Sep 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Alloys and Compounds
Volume: 763
ISSN (Print): 0925-8388
Ratings: 
  • Scopus rating (2018): CiteScore 4.12 SJR 1.065 SNIP 1.386
Original language: English
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Metals and Alloys, Materials Chemistry
Keywords: Degenerated semiconductors, Diluted magnetic semiconductors, Doping, Plasmonic nanocrystals, Solvothermal synthesis, ZnO

Bibliographical note

int=fot,"Joost, Urmas"

Source: Scopus
Source-ID: 85048730804

Research output: Contribution to journalArticleScientificpeer-review

Processing and Characterization of Bioactive Borosilicate Glasses and Scaffolds with Persistent Luminescence

In this proceeding, we report our latest results on the development of borosilicate glasses with persistent luminescence (PeL). Those PeL glasses were processed by adding PeL microparticles (MPs) in the glass using the direct doping method. First, we explain the challenges to balance the survival and dispersion of MPs when preparing borosilicate glasses using this method. Then, we show that scaffold can be obtained using the sintering process from these glasses but also by adding PeL microparticles (MPs) in the glass powder prior to sintering. Finally, we discuss the impact of the scaffold fabrication process on the PeL properties of the MPs.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Biomaterials and Tissue Engineering Group, Photonics, Research group: Photonics Glasses, Turku University of Applied Science
Contributors: Del Cerro, P. R., Saarinen, M., Massera, J., Norrbo, I., Lastusaari, M., Petit, L.
Number of pages: 5
Publication date: 26 Sep 2018

Host publication information

Title of host publication: 2018 20th International Conference on Transparent Optical Networks, ICTON 2018
Volume: 2018-July
Publisher: IEEE COMPUTER SOCIETY PRESS
Article number: 8473916
ISBN (Electronic): 9781538666043

Publication series

Name: Conference proceedings : International Conference on Transparent Optical Networks
ISSN (Print): 2161-2056
ASJC Scopus subject areas: Computer Networks and Communications, Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Keywords: borosilicate glasses, direct particles doping method, Dy microparticles, persistent luminescence, sintering, SrAlO:Eu

Bibliographical note

INT=fot,"Del Cerro, P. Roldan"

Source: Scopus
Source-ID: 85055532457

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Further enhancement of mechanical properties of conducting rubber composites based on multiwalled carbon nanotubes and Nitrile Rubber by solvent treatment

Post-treatment removal of dispersion agents from carbon nanotube/rubber composites can greatly enhance the mechanical properties by increasing the filler-matrix interaction. In this study, multiwall carbon nanotubes (MWNT) were dispersed in water by sonication and nonionic surfactant, octyl-phenol-ethoxylate was used as a dispersion agent. The dispersed MWNTs were incorporated in thermo-reactive acrylonitrile butadiene rubber (NBR) latex and nanocomposite films were prepared by solution casting. As a post-treatment, the surfactant was removed with acetone and films were dried in air. Dispersion quality of the colloid before casting was determined, and mechanical, electrical and thermal properties of the composites before and after the acetone post-treatment were studied. It was found that removal of dispersion agent increased the storage modulus of films between 160-300% in all samples. Relative enhancement was greater in samples with better dispersion quality, whereas thermal conductivity changed more in samples with smaller dispersion quality values. Electrical properties were not notably affected.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Department of Materials Science, Research group: Plastics and Elastomer Technology, Leibniz-Institut für Polymerforschung Dresden E.V.
Contributors: Keinänen, P., Das, A., Vuorinen, J.
Number of pages: 12
Publication date: 23 Sep 2018
Peer-reviewed: Yes

Publication information

Journal: Materials
Volume: 11
Issue number: 10
Article number: 1806
ISSN (Print): 1996-1944
Ratings: 
  • Scopus rating (2018): CiteScore 3.26 SJR 0.686 SNIP 1.2
Original language: English
ASJC Scopus subject areas: Materials Science(all)
Keywords: CNT, Dispersion, Nanocomposite, NBR, Post-treatment
Electronic versions: 
Source: Scopus
Source-ID: 85053892020

Research output: Contribution to journalArticleScientificpeer-review

Mechanical, thermal, and burning properties of viscose fabric composites: Influence of epoxy resin modification

The influence of epoxy resin modification by 3-aminopropyltriethoxysilane (APTES) on various properties of warp knitted viscose fabric is reported in this study. Dynamic mechanical, impact resistance, flexural, thermal properties, and burning behavior of the epoxy/viscose fabric composites are studied with respect to varying content of silane coupling agent. The results obtained for APTES-modified epoxy resin based composites reinforced with unmodified viscose fabric composites are compared to unmodified epoxy resin based composites reinforced with APTES-modified viscose fabric. The dynamic mechanical behavior of the APTES-modified resin based composites indicates improved interfacial adhesion. The composites prepared from modified epoxy resin exhibited a twofold increase in impact resistance. The improved adhesion between the fiber and modified resin was also visible from the scanning electron microscope analysis of the impact fracture surface. There was less influence of resin modification on the flexural properties of the composites. The 5% APTES modification induced early degradation of composites compared to all other composites. The burning rate of all the composites under study is rated to be satisfactory for use in automotive interior applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Centria University of Applied Sciences, University of Borås, Yanbu Industrial College, Jozef Stefan Institute, Swedish Centre for Resource Recovery
Contributors: Rajan, R., Rainosalo, E., Ramamoorthy, S. K., Thomas, S. P., Zavašnik, J., Vuorinen, J., Skrifvars, M.
Publication date: 20 Sep 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Applied Polymer Science
Volume: 135
Issue number: 36
Article number: 46673
ISSN (Print): 0021-8995
Ratings: 
  • Scopus rating (2018): CiteScore 2.25 SJR 0.554 SNIP 0.814
Original language: English
ASJC Scopus subject areas: Chemistry(all), Surfaces, Coatings and Films, Polymers and Plastics, Materials Chemistry
Keywords: cellulose and other wood products, functionalization of polymers, mechanical properties, thermal properties, thermosets

Bibliographical note

EXT="Skrifvars, Mikael"

Source: Scopus
Source-ID: 85049105961

Research output: Contribution to journalArticleScientificpeer-review

A COMPARATIVE IN VITRO STUDY OF CELL GROWTH ON TEXTILE SCAFFOLDS FOR TISSUE ENGINEERING APPLICATIONS

General information

Publication status: Published
MoE publication type: Not Eligible
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Biomaterials and Tissue Engineering Group, Tampere University of Technology, BioMediTech, University of Tampere, BioMediTech, Adult Stem Cell Research Group
Contributors: Kroon, M., Talvitie, E., Miettinen, S., Kellomäki, M.
Publication date: 12 Sep 2018
Peer-reviewed: Unknown
Event: Paper presented at ESB2018 - 29th Annual Meeting of European Society for Biomaterials, Maastricht, Netherlands.
ASJC Scopus subject areas: Biomaterials, Biomedical Engineering

Research output: Other conference contributionPaper, poster or abstractScientific

Performance evaluation of the HR-ELPI + inversion

Data inversion methods used in aerosol measurement instruments have significant influence on the resolution and quality of the result. A freshly launched new electrical low pressure impactor (ELPI) instrument version, high resolution ELPI+ (HR-ELPI+, Dekati Ltd.), uses an iterative inversion calculation method to improve particle size resolution, concentration, and data analysis quality. In this article, the performance of the HR-ELPI + is critically analyzed by simulations and experiments in laboratory and field conditions, and the results are compared with a conventional inversion data analysis method (cut-point diameter concept) and with common reference instruments (e.g., SMPS and EEPS). The results showed that the HR-ELPI + inversion has limited performance at the lower and upper limits of the instrument’s size range, and can suffer if the raw currents have signal dependent noise more than 50% or electric noise more than 1%. However, the HR-ELPI + clearly provide remarkably better resolution and quality with low oscillation risk compared to the conventional cut-point diameter concept of the ELPI. The HR-ELPI + also showed generally very similar size distributions and number concentrations compared to the reference instruments.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics
Contributors: Saari, S., Arffman, A., Harra, J., Rönkkö, T., Keskinen, J.
Number of pages: 11
Pages: 1037-1047
Publication date: 2 Sep 2018
Peer-reviewed: Yes

Publication information

Journal: Aerosol Science and Technology
Volume: 52
Issue number: 9
ISSN (Print): 0278-6826
Ratings: 
  • Scopus rating (2018): CiteScore 2.35 SJR 0.786 SNIP 0.976
Original language: English
ASJC Scopus subject areas: Environmental Chemistry, Materials Science(all), Pollution
Keywords: Pramod Kulkarni
Source: Scopus
Source-ID: 85052142628

Research output: Contribution to journalArticleScientificpeer-review

Post operation inactivation of acidophilic bioleaching microorganisms using natural chloride-rich mine water

The H2020 BIOMOre project (www.biomore.info, Grant Agreement #642456) tests the feasibility of in situ bioleaching of copper in deep subsurface deposits in the Rudna mine, Poland. Copper is leached using biologically produced ferric iron solution, which is recycled back to the in situ reactor after re-oxidation by iron-oxidizing microorganisms. From a post operational point of view, it is important that the biological processes applied during the operation can be controlled and terminated. Our goal was to determine the possibility to use natural saline mine water for the inactivation of the introduced iron-oxidizing microorganisms remaining in the in situ reactor after completion of the leaching process of the ore block. Aerobic and anaerobic microcosms containing acid-leached (pH 2) sandstone or black shale from the Kupferschiefer in the Rudna mine were further leached with the effluent from a ferric iron generating bioreactor at 30 °C for 10 days to simulate the in situ leaching process. After the removal of the iron solution, residing iron-oxidizing microorganisms were inactivated by filling the microcosms with chloride-rich water (65 g L−1 Cl) originating from the mine. The chloride-rich water irreversibly inactivated the iron-oxidizing microorganisms and showed that the naturally occurring saline water of the mine can be used for long-term post process inactivation of bioleaching microorganisms

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, VTT Technical Research Centre of Finland
Contributors: Bomberg, M., Miettinen, H., Wahlström, M., Kaartinen, T., Ahoranta, S., Lakaniemi, A., Kinnunen, P.
Number of pages: 10
Pages: 236-245
Publication date: 1 Sep 2018
Peer-reviewed: Yes

Publication information

Journal: Hydrometallurgy
Volume: 180
ISSN (Print): 0304-386X
Ratings: 
  • Scopus rating (2018): CiteScore 4 SJR 1.014 SNIP 1.817
Original language: English
ASJC Scopus subject areas: Industrial and Manufacturing Engineering, Metals and Alloys, Materials Chemistry
Keywords: BIOMOre, in situ bioleaching, Inactivation, Iron-oxidizing bacteria, Quantitative PCR
Source: Scopus
Source-ID: 85051388591

Research output: Contribution to journalArticleScientificpeer-review

Recent progress in biohydrometallurgy and microbial characterisation

Since the discovery of microbiological metal dissolution, numerous biohydrometallurgical approaches have been developed to use microbially assisted aqueous extractive metallurgy for the recovery of metals from ores, concentrates, and recycled or residual materials. Biohydrometallurgy has helped to alleviate the challenges related to continually declining ore grades by transforming uneconomic ore resources to reserves. Engineering techniques used for biohydrometallurgy span from above ground reactor, vat, pond, heap and dump leaching to underground in situ leaching. Traditionally biohydrometallurgy has been applied to the bioleaching of base metals and uranium from sulfides and the biooxidation of sulfidic refractory gold ores and concentrates before cyanidation. More recently the interest in using bioleaching for oxide ore and waste processing, as well as extracting other commodities such as rare earth elements has been growing. Bioprospecting, adaptation, engineering and storing of microorganisms has increased the availability of suitable biocatalysts for biohydrometallurgical applications. Moreover, the advancement of microbial characterisation methods has increased the understanding of microbial communities and their capabilities in the processes. This paper reviews recent progress in biohydrometallurgy and microbial characterisation.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, CSIRO Land and Water, School of Biomedical Sciences, University of Western Australia, CSIRO Mineral Resources, Murdoch University
Contributors: Kaksonen, A. H., Boxall, N. J., Gumulya, Y., Khaleque, H. N., Morris, C., Bohu, T., Cheng, K. Y., Usher, K. M., Lakaniemi, A.
Number of pages: 19
Pages: 7-25
Publication date: 1 Sep 2018
Peer-reviewed: Yes

Publication information

Journal: Hydrometallurgy
Volume: 180
ISSN (Print): 0304-386X
Ratings: 
  • Scopus rating (2018): CiteScore 4 SJR 1.014 SNIP 1.817
Original language: English
ASJC Scopus subject areas: Industrial and Manufacturing Engineering, Metals and Alloys, Materials Chemistry
Keywords: Biohydrometallurgy, Bioleaching, Biooxidation, Characterisation, Microbiology

Bibliographical note

EXT="Kaksonen, Anna H."

Source: Scopus
Source-ID: 85049805480

Research output: Contribution to journalArticleScientificpeer-review

Dilute nitride triple junction solar cells for space applications: Progress towards highest AM0 efficiency

We report a detailed performance assessment of triple junction dilute nitride solar cells fabricated by a combined molecular beam epitaxy-metal organic chemical vapor deposition process and designed for space applications. The experimental sample exhibits an efficiency level of 30.8% under AM0 illumination. Analyses of the isotype single junction dilute nitride bottom cells reveal a band gap voltage offset of 0.49 V at one sun illumination and a value as low as 0.47 V for full spectrum excitation without filter layers. The analyses point out the limitation of the design in terms of current balancing. With optimized design, an efficiency of 32.1% is possible, revealing the maturity reached by dilute nitride technology in the quest for improving the efficiency of lattice-matched multijunction solar cells.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC, CESI S.p.A.
Contributors: Aho, A., Isoaho, R., Tukiainen, A., Gori, G., Campesato, R., Guina, M.
Number of pages: 5
Pages: 740-744
Publication date: Sep 2018
Peer-reviewed: Yes
Early online date: Apr 2018

Publication information

Journal: Progress in Photovoltaics: Research and Applications
Volume: 26
Issue number: 19
ISSN (Print): 1062-7995
Ratings: 
  • Scopus rating (2018): CiteScore 6.68 SJR 1.942 SNIP 2.413
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Renewable Energy, Sustainability and the Environment, Condensed Matter Physics, Electrical and Electronic Engineering
Source: Scopus
Source-ID: 85045098254

Research output: Contribution to journalArticleScientificpeer-review

Fluorescence bandwidth of 280nm from broadband Ce3+-doped silica fiber pumped with blue laser diode

Fluorescence properties of a Ce3+-doped silica fiber at different pump wavelengths between 405nm to 450 nm are investigated. With 405 nm pump wavelength and a fiber length of ∼130-140 cm broadband fluorescence of ∼280nm is achieved.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Photonics, Research group: Nanophotonics, Aston University, Fiber Optics Research Center of the Russian Academy of Sciences, Russian Academy of Sciences
Contributors: Yadav, A., Chichkov, N. B., Gumenyuk, R., Zherebtsov, E., Melkumov, M. A., Yashkov, M. V., Dianov, E. M., Rafailov, E. U.
Number of pages: 1
Pages: 133-133
Publication date: 13 Aug 2018

Host publication information

Title of host publication: 2018 International Conference Laser Optics (ICLO)
Publisher: IEEE
Article number: 8435861
ISBN (Electronic): 9781538636121
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Keywords: Broadband source, Ce-doped fiber, Ce ions, Fluorescence
Source: Scopus
Source-ID: 85052525711

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Extending the Faraday cup aerosol electrometer based calibration method up to 5 µm

A Faraday cup aerosol electrometer based electrical aerosol instrument calibration setup from nanometers up to micrometers has been designed, constructed, and characterized. The set-up utilizes singly charged seed particles, which are grown to the desired size by condensation of diethylhexyl sebacate. The calibration particle size is further selected with a Differential Mobility Analyzer (DMA). For micrometer sizes, a large DMA was designed, constructed, and characterized. The DMA electrical mobility resolution was found to be 7.95 for 20 L/min sheath and 2 L/min sample flows. The calibration is based on comparing the instrument’s response against the concentration measured with a reference Faraday cup aerosol electrometer. The set-up produces relatively high concentrations in the micrometer size range (more than 2500 1/cm3 at 5.3 µm). A low bias flow mixing and splitting between the reference and the instrument was constructed from a modified, large-sized mixer and a four-port flow splitter. It was characterized at different flow rates and as a function of the particle size. Using two of the four outlet ports at equal 1.5 L/min flow rates, the particle concentration bias of the flow splitting was found to be less than ±1% in the size range of 3.6 nm–5.3 µm. The developed calibration set-up was used to define the detection efficiency of a condensation particle counter from 3.6 nm to 5.3 µm with an expanded measurement uncertainty (k = 2) of less than 4% over the entire size range and less than 2% for most of the measurement points.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: The Instrumentation, Emissions, and Atmospheric Aerosols Group, Research area: Aerosol Physics
Contributors: Järvinen, A., Keskinen, J., Yli-Ojanperä, J.
Number of pages: 13
Pages: 828-840
Publication date: 3 Aug 2018
Peer-reviewed: Yes

Publication information

Journal: Aerosol Science and Technology
Volume: 52
Issue number: 8
ISSN (Print): 0278-6826
Ratings: 
  • Scopus rating (2018): CiteScore 2.35 SJR 0.786 SNIP 0.976
Original language: English
ASJC Scopus subject areas: Environmental Chemistry, Materials Science(all), Pollution
Keywords: Pramod Kulkarni
Source: Scopus
Source-ID: 85051115278

Research output: Contribution to journalArticleScientificpeer-review

Enhanced resonant nonlinear absorption and optical limiting in Er3+ ions doped multicomponent tellurite glasses

Nonlinear optical properties of multicomponent tellurite glasses doped with Er3+ ions were investigated by open aperture Z-scan measurements. Compositional and linear optical properties of the glasses were examined by the energy dispersive X-ray spectrum and UV–vis–NIR absorption spectrum analysis respectively. The mechanism behind the optical nonlinearity and optical limiting efficiency was successfully explained by evaluating the physical properties such as density, refractive index and polarizability of the glasses. The nonlinear properties critically depend on the polarizability, which is found to increase with the addition of Er3+ ions by the creation of non-bridging oxygen ions. By the systematic addition of Er3+ ions, we have dictated the physical properties and thus tuned the optical limiting efficiency of the glasses. This makes the Er3+-doped multicomponent tellurite glasses flexible tunable optical limiters for potential device applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Mahatma Gandhi University
Contributors: Sajna, M. S., Perumbilavil, S., Prakashan, V. P., Sanu, M. S., Joseph, C., Biju, P. R., Unnikrishnan, N. V.
Number of pages: 9
Pages: 227-235
Publication date: 1 Aug 2018
Peer-reviewed: Yes

Publication information

Journal: Materials Research Bulletin
Volume: 104
ISSN (Print): 0025-5408
Ratings: 
  • Scopus rating (2018): CiteScore 3.12 SJR 0.744 SNIP 0.907
Original language: English
ASJC Scopus subject areas: Materials Science(all), Condensed Matter Physics, Mechanics of Materials, Mechanical Engineering
Keywords: Multiphoton absorption, Optical limiting, Optical nonlinearity, Tellurite glasses, Z-scan technique
Source: Scopus
Source-ID: 85046365437

Research output: Contribution to journalArticleScientificpeer-review

High surface quality welding of aluminum using adjustable ring-mode fiber laser

A method to improve penetration and stabilize the welding phenomenon at a high welding speed has been described through experimental and numerical investigations. Using a high power laser beam consisting of a center and a ring part, influences of shielding gas direction and flow rate, laser power density, and welding mode defined by variable intensity distribution have been clarified. The weld bead was evaluated in terms of width, height, shape and roughness. Dual-mode laser irradiation of center and ring power made it possible to stabilize the welding process. The center power helps to achieve sufficient deep penetration, while ring power ensures good temperature distribution. Good surface quality and deep penetration welding could be achieved with dual-mode welding, using low flow rate of shielding gas supplied from the backside direction.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Mechanical Engineering and Industrial Systems, Okayama University, Corelase Oy
Contributors: Maina, M. R., Okamoto, Y., Okada, A., Närhi, M., Kangastupa, J., Vihinen, J.
Number of pages: 9
Pages: 180-188
Publication date: 1 Aug 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Materials Processing Technology
Volume: 258
ISSN (Print): 0924-0136
Ratings: 
  • Scopus rating (2018): CiteScore 5.08 SJR 1.719 SNIP 2.773
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Computer Science Applications, Metals and Alloys, Industrial and Manufacturing Engineering
Keywords: Adjustable ring-mode fiber laser, Aluminum, Laser welding, Shielding gas, Surface quality
Source: Scopus
Source-ID: 85044959061

Research output: Contribution to journalArticleScientificpeer-review

Near-threshold high spin amplification in a 1300 nm GaInNAs spin laser

Using continuous-wave optical pumping of a spin-VCSEL at room temperature, we find high spin amplification of the pump close to threshold within the communications wavelength window, here at 1300 nm. This facilitates a strong switch from left to right circularly polarised light emission, which has potential applications in polarisation encoding for data communications. We use a simple spin flip model to fit the experimental results and discuss the VCSEL parameters that affect this amplification.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC, Research group: Semiconductor Technology and Applications, University of Essex, University of Bristol
Contributors: Cemlyn, B., Adams, M., Harbord, E., Li, N., Henning, I. D., Oulton, R., Korpijärvi, V. M., Guina, M.
Publication date: 1 Aug 2018
Peer-reviewed: Yes

Publication information

Journal: Semiconductor Science and Technology
Volume: 33
Issue number: 9
Article number: 094005
ISSN (Print): 0268-1242
Ratings: 
  • Scopus rating (2018): CiteScore 2.4 SJR 0.744 SNIP 1.002
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering, Materials Chemistry
Keywords: spin amplification, spin laser, spin VCSEL
Source: Scopus
Source-ID: 85053167963

Research output: Contribution to journalArticleScientificpeer-review

Geometry Analysis in Screen-Printed Stretchable Interconnects

Deformability of interconnects and conductors as the skeleton of soft electronic devices plays an important role in the stretchability of the whole system. To make the interconnects stretchable, either employing deformable materials or tailoring the design are the primary approaches. It is also possible to combine the two strategies. In advanced stretchable electronic circuits, there is a frequently need for the interconnects to transform from a narrow to a wide geometry. Therefore, this paper assesses three different geometries that accommodate a narrow-to-wide transition along the interconnects. First, the geometry is modeled using Finite Element (FE) analysis. Second, in order to verify the accuracy of the FE model, screen-printed interconnects are fabricated accordingly by using silver flake ink on a deformable substrate. The geometrical modification shows a considerable improvement in the stretchability of the whole system. Additionally, the effect of encapsulation with thermoplastic polyurethane (TPU) on the performance of stretchable interconnects is investigated.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electronics and Communications Engineering, Materials Science
Contributors: Mosallaei, M., Jokinen, J., Honkanen, M., Iso-Ketola, P., Vippola, M., Vanhala, J., Kanerva, M., Mantysalo, M.
Pages: 1344-1352
Publication date: Aug 2018
Peer-reviewed: Yes
Early online date: 8 Jul 2018

Publication information

Journal: IEEE Transactions on Components, Packaging and Manufacturing Technology
Volume: 8
Issue number: 8
ISSN (Print): 2156-3950
Ratings: 
  • Scopus rating (2018): CiteScore 2.26 SJR 0.552 SNIP 1.236
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Industrial and Manufacturing Engineering, Electrical and Electronic Engineering
Keywords: Conductivity, finite element analysis, Geometry, Integrated circuit interconnections, Plastics, printed electronics, screen-printing, Strain, Stress, stretchable interconnects., Substrates
Source: Scopus
Source-ID: 85049772255

Research output: Contribution to journalArticleScientificpeer-review

Design aspects of all atomic layer deposited TiO2–Fe2O3 scaffold-absorber photoanodes for water splitting

Iron and titanium oxides have attracted substantial attention in photoelectrochemical water splitting applications. However, both materials suffer from intrinsic limitations that constrain the final device performance. In order to overcome the limitations of the two materials alone, their combination has been proposed as a solution to the problems. Here we report on the fabrication of an atomic layer deposited (ALD) Fe2O3 coating on porous ALD-TiO2. Our results show that successful implementation requires complete mixing of the TiO2 and Fe2O3 layers via annealing resulting in the formation of a photoactive iron titanium oxide on the surface. Moreover, we found that incomplete mixing leads to crystallization of Fe2O3 to hematite that is detrimental to the photoelectrochemical performance. IPCE and transient photocurrent measurements performed using UV and visible light excitation confirmed that the iron titanium oxide extends the photocurrent generation to the visible range. These measurements were complemented by transient absorption spectroscopy (TAS), which revealed a new band absent in pristine hematite or anatase TiO2 that we assign to charge transfer within the structure. Taken together, these results provide design guidelines to be considered when aiming to combine TiO2 and Fe2O3 for photoelectrochemical applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Research group: Chemistry & Advanced Materials, Research group: Surface Science, Photonics, Materials Science, Research group: Plastics and Elastomer Technology
Contributors: Hiltunen, A., Ruoko, T., Iivonen, T., Lahtonen, K., Ali-Löytty, H., Sarlin, E., Valden, M., Leskelä, M., Tkachenko, N.
Pages: 2124-2130
Publication date: 31 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: Sustainable Energy & Fuels
Volume: 2
Issue number: 9
ISSN (Print): 2398-4902
Ratings: 
  • Scopus rating (2018): CiteScore 4.94 SNIP 0.841
Original language: English
ASJC Scopus subject areas: Electrochemistry, Renewable Energy, Sustainability and the Environment, Surfaces, Coatings and Films
Keywords: Water splitting, Atomic layer deposition (ALD), Titanium dioxide, Hematite, Cellulose, Template

Research output: Contribution to journalArticleScientificpeer-review

Processing of printed silver patterns on an ETFE substrate

Printed electronics makes it possible to fabricate devices on thin and flexible substrates at a low cost and with simple processing. However, substrate characteristics can make patterning challenging. Here, we report our approach for processing printed silver patterns on an extremely hydrophobic ethylene-Tetrafluoroethylene (ETFE) foil substrate. The effects of selected surface modification methods on substrate characteristics and final print quality were studied, and the thermal characteristics of ETFE were determined. Conductive silver patterns were fabricated using both screen printing and inkjet printing techniques. Additionally, intense pulse light method was compared to thermal annealing as an alternative annealing method. The surface modification of ETFE was observed to affect ink wetting and print quality. It was concluded that the impact of the chosen annealing method on the final characteristics of the printed structures was significant.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Electronics and Communications Engineering, Trelic Ltd.
Contributors: Mikkonen, R., Lahokallio, S., Frisk, L., Mäntysalo, M.
Number of pages: 7
Pages: 1-7
Publication date: 31 Jul 2018

Host publication information

Title of host publication: Proceedings - 2018 IMAPS Nordic Conference on Microelectronics Packaging, NORDPAC 2018
Publisher: IEEE
Article number: 8423860
ISBN (Print): 9789526815053
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering
Keywords: DSC, ETFE, IPL, Printed electronics, TMA

Bibliographical note

EXT="Lahokallio, Sanna"
EXT="Frisk, Laura"

Source: Scopus
Source-ID: 85051476038

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Wound healing of human embryonic stem cell-derived retinal pigment epithelial cells is affected by maturation stage

Background: Wound healing of retinal pigment epithelium (RPE) is a complex process that may take place in common age-related macular degeneration eye disease. The purpose of this study was to evaluate whether wounding and wound healing has an effect on Ca2+ dynamics in human embryonic stem cell (hESC)-RPEs cultured different periods of time. Methods: The 9-day-cultured or 28-day-cultured hESC-RPEs from two different cell lines were wounded and the dynamics of spontaneous and mechanically induced intracellular Ca2+ activity was measured with live-cell Ca2+ imaging either immediately or 7days after wounding. The healing time and speed were analyzed with time-lapse bright field microscopy. The Ca2+ activity and healing speed were analysed with image analysis. In addition the extracellular matrix deposition was assessed with confocal microscopy. Results: The Ca2+ dynamics in hESC-RPE monolayers differed depending on the culture time: 9-day-cultured cells had higher number of cells with spontaneous Ca2+ activity close to freshly wounded edge compared to control areas, whereas in 28-day-cultured cells there was no difference in wounded and control areas. The 28-day-cultured, wounded and 7-day-healed hESC-RPEs produced wide-spreading intercellular Ca2+ waves upon mechanical stimulation, while in controls propagation was restricted. Most importantly, both wave spreading and spontaneous Ca2+ activity of cells within the healed area, as well as the cell morphology of 28-day-cultured, wounded and thereafter 7-day-healed areas resembled the 9-day-cultured hESC-RPEs. Conclusions: This acquired knowledge about Ca2+ dynamics of wounded hESC-RPE monolayers is important for understanding the dynamics of RPE wound healing, and could offer a reliable functionality test for RPE cells. The data presented in here suggests that assessment of Ca2+ dynamics analysed with image analysis could be used as a reliable non-invasive functionality test for RPE cells.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Computational Biophysics and Imaging Group, University of Eastern Finland, University Central Hospital Kuopio
Contributors: Abu Khamidakh, A. E., Rodriguez-Martinez, A., Kaarniranta, K., Kallioniemi, A., Skottman, H., Hyttinen, J., Juuti-Uusitalo, K.
Publication date: 31 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: BioMedical Engineering Online
Volume: 17
Issue number: 1
Article number: 102
ISSN (Print): 1475-925X
Ratings: 
  • Scopus rating (2018): CiteScore 2.44 SJR 0.595 SNIP 1.047
Original language: English
ASJC Scopus subject areas: Radiological and Ultrasound Technology, Biomaterials, Biomedical Engineering, Radiology Nuclear Medicine and imaging
Keywords: Ca waves, Cell maturation, HESC-RPE, Image analysis, Mechanical stimulation, Mechanically induced intercellular Ca waves, RPE, Spontaneous [Ca] increases, Wound healing
Electronic versions: 
Source: Scopus
Source-ID: 85050745629

Research output: Contribution to journalArticleScientificpeer-review

Exciton localization and structural disorder of GaAs1-xBix/GaAs quantum wells grown by molecular beam epitaxy on (311)B GaAs substrates

In this work, we have investigated the structural and optical properties of GaAs(1-x)Bix/GaAs single quantum wells (QWs) grown by molecular beam epitaxy on GaAs (311)B substrates using x-ray diffraction, atomic force microscopy, Fourier-transform Raman (FT-Raman) and photoluminescence spectroscopy techniques. The FT-Raman results revealed a decrease of the relative intensity ratio of transverse and longitudinal optical modes with the increase of Bi concentration, which indicates a reduction of the structural disorder with increasing Bi incorporation. In addition, the PL results show an enhancement of the optical efficiency of the structures as the Bi concentration is increased due to important effects of exciton localization related to Bi defects, nonradiative centers and alloy disorder. These results provide evidence that Bi is incorporated effectively into the QW region. Finally, the temperature dependence of the PL spectra has evidenced two distinct types of defects related to the Bi incorporation, namely Bi clusters and pairs, and alloy disorder and potential fluctuation.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC, Universidade Federal de São Carlos, University of Nottingham, Adana Science and Technology University, University of São Paulo
Contributors: Prando, G. A., Orsi Gordo, V., Puustinen, J., Hilska, J., Alghamdi, H. M., Som, G., Gunes, M., Akyol, M., Souto, S., Rodrigues, A. D., Galeti, H. V., Henini, M., Gobato, Y. G., Guina, M.
Publication date: 17 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: Semiconductor Science and Technology
Volume: 33
Issue number: 8
Article number: 084002
ISSN (Print): 0268-1242
Ratings: 
  • Scopus rating (2018): CiteScore 2.4 SJR 0.744 SNIP 1.002
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering, Materials Chemistry
Keywords: dilute bismide, exciton localization, photoluminescence, structural disorder
Source: Scopus
Source-ID: 85051332383

Research output: Contribution to journalArticleScientificpeer-review

Fluid flow simulations meet high-speed video: Computer vision comparison of droplet dynamics

Hypothesis: While multiphase flows, particularly droplet dynamics, are ordinary in nature as well as in industrial processes, their mathematical and computational modelling continue to pose challenging research tasks - patent approaches for tackling them are yet to be found. The lack of analytical flow field solutions for non-trivial droplet dynamics hinders validation of computer simulations and, hence, their application in research problems. High-speed videos and computer vision algorithms can provide a viable approach to validate simulations directly against experiments. Experiments: Droplets of water (or glycerol-water mixtures) impacting on both hydrophobic and superhydrophobic surfaces were imaged with a high-speed camera. The corresponding configurations were simulated using a lattice-Boltzmann multiphase scheme. Video frames from experiments and simulations were compared, by means of computer vision, over entire droplet impact events. Findings: The proposed experimental validation procedure provides a detailed, dynamic one-on-one comparison of a droplet impact. The procedure relies on high-speed video recording of the experiments, computer vision, and on a software package for the analyzation routines. The procedure is able to quantitatively validate computer simulations against experiments and it is widely applicable to multiphase flow systems in general.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Natural Resources Institute Finland (Luke), BioFluidix GmbH, Faculty of Information Technology, Jyväskylän yliopisto
Contributors: Kulju, S., Riegger, L., Koltay, P., Mattila, K., Hyväluoma, J.
Number of pages: 9
Pages: 48-56
Publication date: 15 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Colloid and Interface Science
Volume: 522
ISSN (Print): 0021-9797
Ratings: 
  • Scopus rating (2018): CiteScore 5.93 SJR 1.29 SNIP 1.322
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Biomaterials, Surfaces, Coatings and Films, Colloid and Surface Chemistry
Keywords: Computer vision, Droplet, Experimental, High-speed video, Hydrophobic, Lattice Boltzmann, Simulation

Bibliographical note

EXT="Kulju, S."

Source: Scopus
Source-ID: 85044153494

Research output: Contribution to journalArticleScientificpeer-review

Mechanical stress analysis during a quench in CLIQ protected 16 T dipole magnets designed for the future circular collider

Protecting the magnets in case of a quench is a challenge for the 16 T superconducting dipole magnets presently designed for the 100 TeV: Future Circular Collider (FCC). These magnets are driven to the foreseen technological limits in terms of critical current, mechanical strength and quench protection. The magnets are protected with CLIQ (Coupling-Loss Induced Quench) system, which is a recently developed quench protection method based on discharging a capacitor bank across part of the winding. The oscillation of the magnet currents and the dissipation of the high stored energy into the windings cause electrodynamic forces and thermal stresses, which may need to be considered in the magnet mechanical design. This paper focuses on mechanical stress analysis during a quench of the 16 T cos-θ and block type dipole magnets. A finite element model allowed studying the stress due to the non-uniform temperature and current distribution in the superconducting coils. Two different CLIQ configurations were considered for the cos-θ design and one for the block type magnet. The analyses of the mechanical behavior of two magnets during a quench without or with hot spot turn were separately carried out. The simulation results show that the stress related to a quench should be considered when designing a high field magnet.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, Research group: Modelling and superconductivity, Lanzhou University, European Organization for Nuclear Research, Laboratorio Accelatori e Superconduttività Applicata, French Atomic Energy Commission (CEA) Saclay, Università degli Studi di Milano
Contributors: Zhao, J., Prioli, M., Stenvall, A., Salmi, T., Gao, Y., Caiffi, B., Lorin, C., Marinozzi, V., Farinon, S., Sorbi, M.
Number of pages: 8
Pages: 27-34
Publication date: 15 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: Physica C: Superconductivity and its Applications
Volume: 550
ISSN (Print): 0921-4534
Ratings: 
  • Scopus rating (2018): CiteScore 1.46 SJR 0.463 SNIP 0.905
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Energy Engineering and Power Technology, Electrical and Electronic Engineering
Keywords: Accelerator magnet, CLIQ protection system, Finite element analysis, Lorentz forces, Quench, Thermal stress
Source: Scopus
Source-ID: 85045717268

Research output: Contribution to journalArticleScientificpeer-review

Directions in QPPR development to complement the predictive models used in risk assessment of nanomaterials

There is an increasing need for predictive risk assessment of nanomaterials (NMs) using methods that are rapid, accurate and resource efficient. To fulfill this need, the development and use of Quantitative Property Property Relationships (QPPRs) for estimating the hazard of NMs and NM-related parameters in exposure modelling seems eminent. In this study, we analyze a selection of models used for hazard and/or exposure assessment of NMs. This analysis was done by identifying all the NM-related properties used in these models related to three categories of data: (i) Intrinsic properties specific to the NM, matrix or experimental conditions, (ii) Extrinsic NM properties related to interaction between the intrinsic properties and (iii) Measured hazard or exposure data. This analysis is combined with the current state of QPPR development to recommend further development of QPPRs for predictive risk assessment of NMs. In particular, the use of descriptors related to the interaction between a NM and its surroundings, e.g. the attachment efficiency is proposed.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: The Instrumentation, Emissions, and Atmospheric Aerosols Group, Research area: Aerosol Physics, National Institute for Public Health and the Environment, Radboud University Nijmegen, Leiden University
Contributors: Quik, J. T., Bakker, M., van de Meent, D., Poikkimäki, M., Dal Maso, M., Peijnenburg, W.
Number of pages: 9
Pages: 58-66
Publication date: 1 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: NanoImpact
Volume: 11
ISSN (Print): 2452-0748
Ratings: 
  • Scopus rating (2018): CiteScore 5.52 SJR 1.322 SNIP 0.936
Original language: English
ASJC Scopus subject areas: Materials Science (miscellaneous), Safety, Risk, Reliability and Quality, Safety Research, Public Health, Environmental and Occupational Health
Keywords: In silico, Modelling, Nanomaterial, QNAR, QPPR, Risk assessment
URLs: 
Source: Scopus
Source-ID: 85042321286

Research output: Contribution to journalArticleScientificpeer-review

Evaluation of screen printed silver trace performance and long-term reliability against environmental stress on a low surface energy substrate

Otherwise attractive substrate materials for printed electronics may have such surface characteristics that make patterning challenging. This article focuses on the printability and performance characterization of conductive patterns on a low surface energy substrate. Surface characteristics of a hydrophobic polyphenylene ether (PPE) substrate and the effects of surface modification using chemical and physical pre-treatments were studied. In addition, silver ink performance and its reliability on this substrate were evaluated. The surface was characterized by surface energy measurements and surface profile analysis. Screen-printed test patterns were characterized to evaluate print quality and electrical and mechanical performance. A further inspection of substrate-ink interactions was conducted using environmental reliability tests. It was observed that ink adhesion could be significantly promoted by choosing a suitable surface pre-treatment method. Low sheet resistances were obtained, and thus, suitable inks for further characterization were found. In addition, it was observed that environmental stress has a significant impact on ink-substrate interactions.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electronics and Communications Engineering, Nano Communication Centre
Contributors: Mikkonen, R., Mäntysalo, M.
Number of pages: 12
Pages: 54-65
Publication date: 1 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: Microelectronics Reliability
Volume: 86
ISSN (Print): 0026-2714
Ratings: 
  • Scopus rating (2018): CiteScore 1.7 SJR 0.376 SNIP 0.983
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Condensed Matter Physics, Safety, Risk, Reliability and Quality, Surfaces, Coatings and Films, Electrical and Electronic Engineering
Keywords: Adhesion, Environmental stress, PPE, Printed electronics, Reliability, Surface modification
Source: Scopus
Source-ID: 85047240351

Research output: Contribution to journalArticleScientificpeer-review

Persistent luminescent borosilicate glasses using direct particles doping method

Persistent luminescence (PeL) was obtained, from the first time to the best of our knowledge, from borosilicate bulk glasses. The glasses were prepared using direct doping method. Commercial PeL SrAl2O4:Eu2+,Dy3+ microparticles (MPs) were added in the borosilicate glass after melting. The persistent luminescence can be augmented when casting the glass 3 min after adding the MPs at 950 °C. Although the borosilicate glasses exhibit persistent luminescence, the glass melt has a corrosive behavior on the MPs leading to the diffusion of Al and Sr into the glasses.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Turku University of Applied Science
Contributors: Roldán Del Cerro, P., Salminen, T., Lastusaari, M., Petit, L.
Number of pages: 4
Pages: 38-41
Publication date: 1 Jul 2018
Peer-reviewed: Yes

Publication information

Journal: Scripta Materialia
Volume: 151
ISSN (Print): 1359-6462
Ratings: 
  • Scopus rating (2018): CiteScore 5.03 SJR 2.185 SNIP 1.95
Original language: English
ASJC Scopus subject areas: Materials Science(all), Condensed Matter Physics, Mechanics of Materials, Mechanical Engineering, Metals and Alloys
Keywords: Borosilicate glasses, Corrosion, Direct particle doping method, Persistent luminescence, SrAlO:Eu,Dy microparticles
Source: Scopus
Source-ID: 85056171139

Research output: Contribution to journalArticleScientificpeer-review

Luminescence of Er3+ doped oxyfluoride phosphate glasses and glass-ceramics

Glasses with the composition (75 NaPO3-(25-x) CaO-xCaF2) (in mol %) were prepared with 0.15 mol% of Er2O3. The effect of the glass composition and of heat treatment on the spectroscopic properties of the newly developed glasses is reported. With the progressive replacement of CaO by CaF2, the Er3+:4I13/2 lifetime and the intensity of the upconversion emission increase whereas the intensity of the emission at 1.5 μm decreases due to the decrease in the phonon energy in the as-prepared glasses. The glasses were heat treated at 20 °C above their respective glass transition temperature for 17 h to form nuclei and then at their crystallization temperature from 15min to 1 h to grow the nuclei into crystals. The heat treatment leads to the precipitation of crystalline phases, the composition of which depends upon the glass composition. As the Er3+:4I13/2 lifetime increases and the intensity of the upconversion increases for the glass with x = 0 after heat treatment, the Er3+ ions are expected to be incorporated into the phosphate-based crystals. However, as the shape of the emission band at 1.5 μm remains unchanged and the intensity of the upconversion decreases significantly after heat treatment of the glasses with x > 10, the crystals found in the glass-ceramics with x > 10 are thought to free of Er3+ ions. Although Er3+ ions entered in the CaF2 crystals precipitating in aluminosilicate glass, the Er3+ ions are believed to remain in the amorphous phosphate part of the glass-ceramic containing CaF2 crystals.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Faculty of Biomedical Sciences and Engineering, Faculty of Engineering Sciences, Research group: Biomaterials and Tissue Engineering Group, Materials Science, Photonics, Istituto Superiore Mario Boella
Contributors: Nommeots-Nomm, A., Boetti, N. G., Salminen, T., Massera, J., Hokka, M., Petit, L.
Number of pages: 7
Pages: 224-230
Publication date: 30 Jun 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Alloys and Compounds
Volume: 751
ISSN (Print): 0925-8388
Ratings: 
  • Scopus rating (2018): CiteScore 4.12 SJR 1.065 SNIP 1.386
Original language: English
ASJC Scopus subject areas: Mechanics of Materials, Mechanical Engineering, Metals and Alloys, Materials Chemistry
Keywords: CaF crystals in glass, Er luminescence, Oxyfluoride phosphate glasses and glass-ceramics
Source: Scopus
Source-ID: 85045405038

Research output: Contribution to journalArticleScientificpeer-review

Manufacturing of calibration samples for barkhausen noise method: case studies on temperature controlled laser and hydrogen-oxygen flame

Non-destructive magnetic Barkhausen noise (BN) measurements are most widely used for studying the grinding burns from hardened and ground samples. The formation of the grinding burns occurs due to excess of heat generation and produces thus changes in the residual stresses and microstructure. The BN method can be used for quality control purposes because it is sensitive to changes both in stresses and microstructure. The important part of the BN inspection procedure is the verification that the sensor and the equipment are working properly. One option is to use calibration pieces to evaluate the operation of the sensor before the actual measurements. The best way is to use similar components and same measurement procedure as to be studied. The components should have artificially produced burn marks to mimic the damaged areas of grinding burns. To validate the BN measurement results properly, the BN sensor needs to be verified with both thermally damaged and thermally undamaged sample surfaces.

In this work, two different procedures to manufacture artificial burn marks were studied. A temperature controlled, robotic assisted, laser system was used to perform temperature controlled tempering marks to carburised gear wheel teeth surfaces. Also, hydrogen-oxygen flame with robotic control was used to produce artificial burn marks on the surfaces of carburised gear wheel teeth surfaces.

The aim was to analyse the suitability of thermal damages created by these two methods by comparing the BN readings of them to each other. The new, temperature controlled, laser system was found to produce uniform quality thermal damages. While the hydrogen-oxygen process was found to be more unpredictable and it needs to be controlled extremely carefully i.e. with robotic manipulation of the hydrogen-oxygen flame. The speed of the hydrogen-oxygen flame affected the RMS values greater than the other tested parameters.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Materials Science, Research group: Materials Characterization, Stresstech Oy
Contributors: Santa-aho, S., Deveci, M., Savolainen, S., Vippola, M.
Number of pages: 8
Publication date: 11 Jun 2018

Host publication information

Title of host publication: Proceedings of the 12th ECNDT : June 11-15, Gothenburg, Sweden, 2018
ISBN (Print): 978-91-639-6217-2
ASJC Scopus subject areas: Materials Science(all)
Keywords: Barkhausen noise, calibration sample, laser processing, hydrogen-oxygen flame
Electronic versions: 

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Fabrication and reliability evaluation of passive UHF RFID T-shirts

In this paper, we present textile antennas fabricated for T-shirt RFID applications by cutting from commercially available electro-textile, by sewing with conductive thread, and by 3D printing with stretchable silver ink on a 100 % cotton fabric. The ready tags with attached ICs are coated with a protective stretchable encapsulant. The wireless performance of the T-shirt tags is evaluated initially as well as after seven washing cycles, followed by nine washing-drying cycles in a household washing and drying machines. The initial read ranges of all kinds of tags, when measured on-body, are around 3.5 meters. Based on the reliability testing results, the coating effectively protects the components from cyclic washing and drying.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Wireless Identification and Sensing Systems Research Group, Department of Electronic Engineering, City University of Hong Kong
Contributors: Chen, X., He, H., Ukkonen, L., Virkki, J., Lu, Y., Lam, H.
Number of pages: 4
Pages: 1-4
Publication date: 8 Jun 2018

Host publication information

Title of host publication: 2018 IEEE International Workshop on Antenna Technology, iWAT2018 - Proceedings
Publisher: IEEE
ISBN (Electronic): 9781538618516
ASJC Scopus subject areas: Instrumentation, Computer Networks and Communications, Electronic, Optical and Magnetic Materials
Keywords: 3D Printing, electro-textiles, embroidery, passive UHF RFID, T-shirts, textiles, washing, wearable electronics

Bibliographical note

jufoid=79362

Source: Scopus
Source-ID: 85050037887

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Alkali-silica reaction in Southern-Finland's bridges

In Central Europe and Scandinavia, alkali-aggregate reaction (AAR) typically occurs in massive concrete structures such as bridges and dams. Despite of having similar bedrock with Sweden, Finland has been considered as an AAR free country. The scope of this study was to find out the existence of alkali-silica reaction (ASR) in Finnish bridges. It was also studied how the age of the bridge as well as the aggregate type has affected the occurrence of ASR. The research material consists of 97 condition assessment reports from concrete bridges constructed between 1912 and 1999. The condition assessments were carried out during 2001–2014. All studied bridges are situated in southern or south-western Finland. Alkali-silica reaction was detected by petrographic analysis in 27 bridges, which is 27.8% of all studied bridges. Of the bridges built in the 1970s (38 bridges in the sample) 42.1% was affected by ASR. In the 1960s bridges (33 bridges in the sample) 17.6% was affected. The bridges showing ASR were 31–44 and 43–52 years old, respectively. Thus, there is a potential risk for having ASR damage in concrete bridges also in the Finnish construction and climate. The study shows, however, that the reaction has taken a considerable amount of time to be detected.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Civil Engineering
Contributors: Lahdensivu, J., Köliö, A., Husaini, D.
Number of pages: 7
Pages: 469-475
Publication date: 1 Jun 2018
Peer-reviewed: Yes

Publication information

Journal: Case Studies in Construction Materials
Volume: 8
ISSN (Print): 2214-5095
Ratings: 
  • Scopus rating (2018): CiteScore 2.79 SJR 0.584 SNIP 1.709
Original language: English
ASJC Scopus subject areas: Materials Science (miscellaneous)
Keywords: Alkali-silica reaction, Concrete bridges, Initiation period, Portland cement
Electronic versions: 

Bibliographical note

INT=rak,"Husaini, David"

Source: Scopus
Source-ID: 85045094273

Research output: Contribution to journalArticleScientificpeer-review

Progress on HL-LHC Nb3Sn Magnets

The high-luminosity Large Hadron Collider (HL-LHC) project aims at allowing to increase the collisions in the LHC by a factor of ten in the decade 2025-2035. One essential element is the superconducting magnet around the interaction region points, where the large aperture magnets will be installed to allow to further reduce the beam size in the interaction point. The core of this upgrade is the Nb3Sn triplet, made up of 150-mm aperture quadrupoles in the range of 7-8 m. The project is being shared between the European Organization for Nuclear Research and the US Accelerator Upgrade Program, based on the same design, and on the two strand technologies. The project is ending the short model phase, and entering the prototype construction. We will report on the main results of the short model program, including the quench performance and field quality. A second important element is the 11 T dipole that replaces a standard dipole making space for additional collimators. The magnet is also ending the model development and entering the prototype phase. A critical point in the design of this magnet is the large current density, allowing increase of the field from 8 to 11 T with the same coil cross section as in the LHC dipoles. This is also the first two-in-one Nb3Sn magnet developed so far. We will report the main results on the test and the critical aspects.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, Research area: Power engineering, Research group: Modelling and superconductivity, European Organization for Nuclear Research, Brookhaven National Laboratory, Fermi National Accelerator Laboratory, Lawrence Berkeley National Laboratory
Contributors: Todesco, E., Annarella, M., Ambrosio, G., Apollinari, G., Ballarino, A., Bajas, H., Bajko, M., Bordini, B., Bossert, R., Bottura, L., Cavanna, E., Cheng, D., Chlachidze, G., De Rijk, G., Dimarco, J., Ferracin, P., Fleiter, J., Guinchard, M., Hafalia, A., Holik, E., Izquierdo Bermudez, S., Lackner, F., Marchevsky, M., Loeffler, C., Nobrega, A., Perez, J. C., Prestemon, S., Ravaioli, E., Rossi, L., Sabbi, G., Salmi, T., Savary, F., Schmalzle, J., Stoynev, S., Strauss, T., Tartaglia, M., Vallone, G., Velev, G., Wanderer, P., Wang, X., Willering, G., Yu, M.
Publication date: 1 Jun 2018
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 28
Issue number: 4
Article number: 4008809
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2018): CiteScore 1.65 SJR 0.406 SNIP 0.969
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: niobium-tin, superconducting coils, Superconducting magnets, type II superconductors
Source: Scopus
Source-ID: 85046361406

Research output: Contribution to journalArticleScientificpeer-review

Quench simulation results for a 12-T twin-aperture dipole magnet

A 12-T twin-aperture subscale dipole magnet is being developed for SPPC pre-study at the Institute of High Energy Physics (IHEP). The magnet is comprised of 6 double-pancake coils which include 2 Nb3Sn coils and 4 NbTi coils. As the stored energy of the magnet is 0.452 MJ and the operation margin is only about 20% at 4.2 K, a quick and effective quench protection system is necessary during the test of this high field magnet. For the design of the quench protection system, attention was not only paid to the hotspot temperature and terminal voltage, but also the temperature gradient during the quench process due to the poor mechanical characteristics of the Nb3Sn cables. With the adiabatic analysis, numerical simulation and the finite element simulation, an optimized protection method is adopted, which contains a dump resistor and quench heaters. In this paper, the results of adiabatic analysis and quench simulation, such as current decay, hot-spot temperature and terminal voltage are presented in details.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, Research area: Power engineering, Research group: Modelling and superconductivity, Institute of High Energy Physics Chinese Academy of Science, Chinese Academy of Sciences, University of Science and Technology of China
Contributors: Cheng, D., Salmi, T., Xu, Q., Peng, Q., Wang, C., Wang, Y., Kong, E., Zhang, K.
Number of pages: 7
Pages: 13-19
Publication date: 1 Jun 2018
Peer-reviewed: Yes

Publication information

Journal: Cryogenics
Volume: 92
ISSN (Print): 0011-2275
Ratings: 
  • Scopus rating (2018): CiteScore 1.57 SJR 0.523 SNIP 1.204
Original language: English
ASJC Scopus subject areas: Materials Science(all), Physics and Astronomy(all)
Keywords: Adiabatic analysis, Heater design, Quench protection, Quench simulation
Source: Scopus
Source-ID: 85044967086

Research output: Contribution to journalArticleScientificpeer-review

The effect of carbon and nickel additions on the precursor synthesis of Cr3C2-Ni nanopowder

Decreasing crystal size to nanoscale is a proven method to enhance material properties. In this study, nanosize Cr3C2 and Cr3C2-Ni were synthetized and the reaction sequence was studied. Aqueous precursors using only water-soluble raw materials with varying carbon contents and a nickel addition were spray-dried. Glycine was used as a carbon source and chromium acetate hydroxide as a chromium source in the precursor solutions. Nickel nitrate hexahydrate was introduced as a nickel source to yield a metallic binder into the carbide nanopowder.Resulting powders were heat-treating to identify an applicable precursor composition producing the targeted Cr3C2 phase with crystal size of tens of nanometers. Thermal synthesis tests of the precursor powders to yield Cr3C2 took place at a temperature between 900 and 1300 °C under an Argon atmosphere. The synthesis of nanosize Cr3C2-Ni powder was successful at 1000 °C in 30 min, in a case of the best precursor. In order to produce the carbide phase with no residual oxide traces, relative carbon load has to be 48 wt%, while the stoichiometric amount of carbon in Cr3C2 is 13 wt%. When also introducing the nickel source into the precursor, an even higher carbon load was required. The carbon surplus needed to enable the Cr3C2 synthesis attributes to the non-homogeneity of the precursor composition.The chemical synthesis starting from water-soluble raw materials is a promising way of preparing nanosize Cr3C2-Ni with the targeted phase configuration.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Materials Characterization, VTT Technical Research Centre of Finland
Contributors: Kaunisto, K., Kotilainen, M., Karhu, M., Lagerbom, J., Vuorinen, T., Honkanen, M., Vippola, M., Turunen, E.
Pages: 9338-9346
Publication date: 1 Jun 2018
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Ceramics International
Volume: 44
Issue number: 8
ISSN (Print): 0272-8842
Ratings: 
  • Scopus rating (2018): CiteScore 3.5 SJR 0.888 SNIP 1.279
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Process Chemistry and Technology, Surfaces, Coatings and Films, Materials Chemistry
Keywords: A. Nanosize CrC synthesis, A. Powders: chemical preparation, B. Grain size, D. Carbides, E. Wear parts

Bibliographical note

EXT="Vuorinen, Tommi"
EXT="Lagerbom, Juha"
EXT="Kaunisto, Kimmo"

Source: Scopus
Source-ID: 85042300396

Research output: Contribution to journalArticleScientificpeer-review

Computational design of a novel medium-carbon, low-alloy steel microalloyed with niobium

The design of a new steel with specific properties is always challenging owing to the complex interactions of many variables. In this work, this challenge is dealt with by combining metallurgical principles with computational thermodynamics and kinetics to design a novel steel composition suitable for thermomechanical processing and induction heat treatment to achieve a hardness level in excess of 600 HV with the potential for good fracture toughness. CALPHAD-based packages for the thermodynamics and kinetics of phase transformations and diffusion, namely Thermo-Calc® and JMatPro®, have been combined with an interdendritic segregation tool (IDS) to optimize the contents of chromium, molybdenum and niobium in a proposed medium-carbon low-manganese steel composition. Important factors taken into account in the modeling and optimization were hardenability and as-quenched hardness, grain refinement and alloying cost. For further investigations and verification, the designed composition, i.e., in wt.% 0.40C, 0.20Si, 0.25Mn, 0.90Cr, 0.50Mo, was cast with two nominal levels of Nb: 0 and 0.012 wt.%. The results showed that an addition of Nb decreases the austenite grain size during casting and after slab reheating prior to hot rolling. Validation experiments showed that the predicted properties, i.e., hardness, hardenability and level of segregation, for the designed composition were realistic. It is also demonstrated that the applied procedure could be useful in reducing the number of experiments required for developing compositions for other new steels.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Metals Technology, Univ of Oulu, Materials Science Research Group, EFD Induction a.s
Contributors: Javaheri, V., Nyyssönen, T., Grande, B., Porter, D.
Number of pages: 15
Pages: 2978-2992
Publication date: Jun 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Materials Engineering and Performance
Volume: 27
Issue number: 6
ISSN (Print): 1059-9495
Ratings: 
  • Scopus rating (2018): CiteScore 1.67 SJR 0.541 SNIP 0.868
Original language: English
ASJC Scopus subject areas: Materials Science(all), Mechanics of Materials, Mechanical Engineering
Keywords: CALPHAD, computational design, homogenization, IDS, JMatPro, microsegregation, prior austenite grain size, Thermo-Calc, wear resistance steel
Source: Scopus
Source-ID: 85045890232

Research output: Contribution to journalArticleScientificpeer-review

Influence of the phosphate glass melt on the corrosion of functional particles occurring during the preparation of glass-ceramics

We report our findings on the impact of the glass composition on the corrosion of microparticles occurring during the preparation of glass-ceramics using the direct doping method. Microparticles (MPs) with the composition Sr4Al14O25:Eu2+,Dy3+ with blue-green persistent luminescence were chosen as the changes in their spectroscopic properties can be related to the MPs’ corrosion. The MPs were added in phosphate-based glasses with different compositions. When using the same doping parameters, the glass system with the composition 90NaPO3-10Na2O (mol%) was found to be the least corrosive on the MPs whereas the glass system with the composition 90NaPO3-10NaF (mol%) is the most corrosive on the MPs probably due to their different viscosity at 575 °C, the temperature at which the MPs are added in the glass melts.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Nanophotonics, Turun Yliopisto/Turun Biomateriaalikeskus, Laboratory of Photonics
Contributors: Ojha, N., Laihinen, T., Salminen, T., Lastusaari, M., Petit, L.
Pages: 11807-11811
Publication date: Jun 2018
Peer-reviewed: Yes
Early online date: 1 Jan 2018

Publication information

Journal: Ceramics International
Volume: 44
Issue number: 10
ISSN (Print): 0272-8842
Ratings: 
  • Scopus rating (2018): CiteScore 3.5 SJR 0.888 SNIP 1.279
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Process Chemistry and Technology, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Corrosion, Direct doping method, Glass melt, Phosphate glass-ceramics, SrAlO:Eu, Dy microparticles
Source: Scopus
Source-ID: 85044921933

Research output: Contribution to journalArticleScientificpeer-review

Investigation of REBCO Roebel Cable Irreversible Critical Current Degradation Under Transverse Pressure

The Roebel cable utilized in High Field accelerator magnets is subject to high transversal electromagnetic forces. The conductor response to exerted pressure depends from the geometry and materials of the cable. A transverse loading test was performed for an impregnated cable in cryogenic conditions. The test revealed Roebel cable being able to withstand elevated average pressure level common to dipole magnets, when the pressure load is exerted by a stiff press tool. However, the mechanism for irreversible current degradation during the transverse loading during powering remains so far unknown. This paper focuses on finding likely failure mechanisms when a magnet is powered. The cable is wound with a glass-fiber sleeve and impregnated with epoxy. Epoxy has much lower stiffness than the coated conductor. When the cable is subjected to transverse loading, abrupt changes in cable thickness and material properties may lead to irreversible degradation of the conductor. As the tape crosses the epoxy-filled central gap region of the cable, the discontinuous change of the support stiffness generates bending strains and shear stress in the conductor. The cable is mechanically modeled. By modeling, the measured axial strain limit of the conductor is connected to transverse pressure limit of the cable.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, Civil Engineering, European Organization for Nuclear Research
Contributors: Murtomäki, J. S., Kouhia, R., Stenvall, A., Bottura, L., Kirby, G., van Nugteren, J., DeRijk, G., Rossi, L.
Publication date: Jun 2018
Peer-reviewed: Yes
Early online date: 20 Apr 2018

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 28
Issue number: 4
Article number: 4802506
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2018): CiteScore 1.65 SJR 0.406 SNIP 0.969
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Accelerator dipoles, Conductors, Critical current density (superconductivity), Degradation, Finite Element Methods, Geometry, HTS Cables, HTS Magnets, Load modeling, Strain, Superconducting cables
Source: Scopus
Source-ID: 85045735242

Research output: Contribution to journalArticleScientificpeer-review

The effects of laser patterning 10CeTZP-Al2O3 nanocomposite disc surfaces: Osseous differentiation and cellular arrangement in vitro

Customized square grid arrangements of different groove depths (1.0, 1.5 and 3.0 μm) and separations (10 and 30 μm) were successfully laser patterned, using a nanosecond pulsed fibre laser, on the surface of 10 mol% ceria-stabilized zirconia and alumina (10CeTZP-Al2O3) nanocomposite discs (diameter: 10 mm; thickness: 1.5 mm). The patterned surfaces and the in vitro biological response of osteoblasts (SAOS-2) towards them were thoroughly analysed. In terms of composition, the laser treatment was found to cause superficial monoclinic-tetragonal zirconia phase transformation and alumina evaporation. In vitro, the most effective grid configuration for osseous differentiation was found to be 1.5 μm groove depth and 10 μm groove separation, and confocal microscopy revealed that the cells show a tendency to be sorted as groove depth increases. It is thought that custom-made patterns could be produced to guide cell attachment in vivo, which could favour implant integration and reduce healing time.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Mechanical Engineering and Industrial Systems, Nanoker Research, Universidad de Oviedo
Contributors: Goyos-Ball, L., Prado, C., Díaz, R., Fernández, E., Ismailov, A., Kumpulainen, T., Levänen, E., Torrecillas, R., Fernández, A.
Pages: 9472-9478
Publication date: Jun 2018
Peer-reviewed: Yes
Early online date: 2018

Publication information

Journal: Ceramics International
Volume: 44
Issue number: 8
ISSN (Print): 0272-8842
Ratings: 
  • Scopus rating (2018): CiteScore 3.5 SJR 0.888 SNIP 1.279
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Process Chemistry and Technology, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Alumina, Cellular arrangement, Ceramic nanocomposite, Laser patterning, Osseous differentiation, Zirconia
Source: Scopus
Source-ID: 85042621677

Research output: Contribution to journalArticleScientificpeer-review

Towards REBCO 20T+ Dipoles for Accelerators

ReBCO High Temperature Superconducting (HTS) coated conductor tapes are a promising candidate for pushing the magnetic fields in accelerator magnets well beyond 20 T. They are capable of very high current densities in intense applied magnetic field, have a very high thermal stability, can withstand high transverse pressures and allow operation in 20 to 30 K helium gas flow, potentially reducing operating cost significantly. During the EuCARD2 program significant developments have been made in terms of coil design, manufacturing and testing. Now that EuCARD2 has come to an end, CERN and collaborators are initiating a new program to continue the development of HTS accelerator magnets. This paper presents our initial thoughts on the conceptual design of a 20 T+ accelerator magnet, using the results and technologies from EuCARD2 combined with some new ideas. The paper discusses the options available for the cross-sectional layout, the use of a hybrid configurations including Aligned Block, the design of the coil-ends and dual aperture configurations. Also discussed is the quench protection of the magnets. Due to the high thermal stability of the conductor and high energy densities it will be required to explore an entirely new approach.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, European Organization for Nuclear Research
Contributors: van Nugteren, J., Kirby, G., Murtomaki, J., DeRijk, G., Rossi, L., Stenvall, A.
Publication date: Jun 2018
Peer-reviewed: Yes
Early online date: 27 Mar 2018

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 28
Issue number: 4
Article number:  4008509
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2018): CiteScore 1.65 SJR 0.406 SNIP 0.969
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Accelerator Dipoles, Accelerator magnets, Conductors, Current density, High-temperature superconductors, HTS Magnets, Magnet Stability, Magnet Structure, Perpendicular magnetic anisotropy, Quench Protection, Superconducting magnets
Source: Scopus
Source-ID: 85044849023

Research output: Contribution to journalArticleScientificpeer-review

Role of Oxide Defects in ALD grown TiO2 Coatings on Performance as Photoanode Protection Layer

Photoelectrochemical (PEC) water splitting is one of the potential methods of utilizing solar energy. A major issue for the method and for renewable energy production is the development of an efficient, chemically stable and cost-effective semiconductor photoanode. Recently, titanium dioxide (TiO2) coatings grown by atomic layer deposition (ALD) have appeared to be a promising approach to stabilize semiconductor photoanodes under PEC conditions. In particular, amorphous ALD grown TiO2 has shown exceptional charge transfer properties compared to its crystalline form that are not properly understood yet. Therefore, we target to gain better understanding on the defect structure of ALD grown TiO2 and utilize the information in the development of optimal photoanode protection layer for efficient solar water splitting.

In this work, structural, optical and photoelectrochemical properties of the ALD grown TiO2 films were studied in as-deposited condition and after annealing in air at 500 °C. TiO2 films were grown on n-type phosphorus-doped silicon and fused quartz by ALD at 200 °C using tetrakis(dimethylamido)titanium (TDMAT) and deionized water as precursors. The properties of TiO2 were investigated by X-ray photoelectron spectroscopy (XPS), ellipsometry and UV/Vis/NIR spectrophotometry. In addition, results from X-ray diffraction (XRD), Raman spectroscopy and photoelectrochemical (PEC) cell are discussed.

Based on the results, as-deposited TiO2 is amorphous and absorbs visible light as ''black'' TiO2. After annealing in air at 500 °C TiO2 crystallizes as rutile and becomes ''white'' TiO2 that absorbs light only in the UV region. As-deposited TiO2 contains significant amount of Ti3+/2+ oxygen vacancies that are oxidized as Ti4+ upon annealing in air. In addition, nitrogen is found only in as-deposited titanium dioxide. As-deposited TiO2 is not chemically stable under PEC conditions. In contrast, the annealed TiO2 is chemically stable and showed 0.20 % ABPE efficiency for water splitting reaction.

As a conclusion, Ti3+ defects induce photocorrosion of ALD TiO2 under PEC conditions. After annealing in air at 500 °C ALD TiO2 is chemically stable and it can be used as a photoanode protection layer. In the future, research will be focused on optimizing the properties of ALD TiO2/Si interface and studying the structure of the surface after deposition of nickel electrocatalysts on TiO2/Si photoanode.

General information

Publication status: Published
Organisations: Photonics, Research group: Surface Science
Contributors: Saari, J., Ali-Löytty, H., Valden, M.
Publication date: 29 May 2018
Peer-reviewed: Unknown
Event: Paper presented at Optics & Photonics Days 2018, Jyväskylä, Finland.
ASJC Scopus subject areas: Renewable Energy, Sustainability and the Environment, Surfaces, Coatings and Films
Keywords: Atomic layer deposition, Titanium dioxide, Photoelectrochemical water splitting

Research output: Other conference contributionPaper, poster or abstractScientific

Multiple Access for Visible Light Communications: Research Challenges and Future Trends

The ever-increasing demand of mobile Internet and multimedia services poses unique and significant challenges for current and future generation wireless networks. These challenges are mainly related to the support of massive ubiquitous connectivity, low latency, and highly efficient utilization of spectrum resources. Therefore, it is of a paramount importance to address them in the design and deployment of future wireless networks. To this end, this paper provides a comprehensive overview of multiple access schemes in the context of visible light communications (VLC). Specifically, we initially provide a thorough overview of frequency-domain multiple access techniques for single-A nd multi-carrier systems, which is then followed by an in-depth discussion on the technical considerations of optical code-division multiple access techniques and their adoption in indoor VLC applications. Furthermore, we address space-division multiple access and, finally, we revisit and analyze a new promising technology, namely, non-orthogonal multiple access (NOMA). It is shown that NOMA exhibits significant benefits in VLC systems that can outperform conventional multiple access schemes, rendering it a particularly effective solution. Furthermore, it is demonstrated that it can coexist with the above optical multiple access schemes, which can maximize the performance and efficiency of future VLC systems. However, it is also shown that the potential of NOMA in VLC systems requires efficient addressing of a series of related challenges and constraints, such as fast and effective successive interference cancellation techniques, compensation and mitigation of LED non-linearity, and imperfect and/or outdated channel state information.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Wireless Communications and Positioning, Electronics and Communications Engineering, Khalifa University, University of Surrey, Aristotle University of Thessaloniki
Contributors: Bawazir, S. S., Sofotasios, P. C., Muhaidat, S., Al-Hammadi, Y., Karagiannidis, G. K.
Number of pages: 8
Pages: 26167-26174
Publication date: 18 May 2018
Peer-reviewed: Yes

Publication information

Journal: IEEE Access
Volume: 6
ISSN (Print): 2169-3536
Ratings: 
  • Scopus rating (2018): CiteScore 4.96 SJR 0.609 SNIP 1.718
Original language: English
ASJC Scopus subject areas: Computer Science(all), Materials Science(all), Engineering(all)
Keywords: Non-orthogonal multiple access, optical multiple access, optical wireless communications, visible light communications
Source: Scopus
Source-ID: 85047225994

Research output: Contribution to journalArticleScientificpeer-review

Morphology evolution of PS-b-PDMS block copolymer and its hierarchical directed self-assembly on block copolymer templates

Cylinder-forming polystyrene-block-polydimethylsiloxane (PS-b-PDMS, 27.2k-b-11.7k, SD39) block copolymer having a total molecular weight of 39 kg mol−1 was exploited to achieve in-plane morphologies of lines, dots and antidots. Brush-free self-assembly of the SD39 on silicon substrates was investigated using solvents that were PS or PDMS selective, neutral and non-solvents based on their Hansen solubility parameters. The different morphologies were achieved with annealing times ranging from 10 min to 1 h at room temperature. The SD39 patterns were used as an etch mask for transferring the pattern into the underlying substrate. Directed self-assembly and hierarchical directed self-assembly on block copolymer templates for confinement of dots was successfully demonstrated. The strategy for achieving multiple morphologies using one BCP by mere choice of the annealing solvents on unmodified substrates provides a simplified method for surface nanopatterning, templated growth of nanomaterials and nanofabrication.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Danmarks Tekniske Universitet, DTU Informatik, Trinity College Dublin, Laboratory of Photonics
Contributors: Rasappa, S., Schulte, L., Borah, D., Hulkkonen, H., Ndoni, S., Salminen, T., Senthamaraikanan, R., Morris, M. A., Niemi, T.
Number of pages: 7
Pages: 1-7
Publication date: 15 May 2018
Peer-reviewed: Yes

Publication information

Journal: Microelectronic Engineering
Volume: 192
ISSN (Print): 0167-9317
Ratings: 
  • Scopus rating (2018): CiteScore 1.91 SJR 0.561 SNIP 0.917
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Condensed Matter Physics, Surfaces, Coatings and Films, Electrical and Electronic Engineering
Keywords: Block copolymer, Hansen solubility, Hierarchical self-assembly, Selective solvent
Source: Scopus
Source-ID: 85041706803

Research output: Contribution to journalArticleScientificpeer-review

Wet etching of dilute nitride GaInNAs, GaInNAsSb, and GaNAsSb alloys lattice-matched to GaAs

We have studied the etching of GaInNAs, GaInNAsSb, and GaNAsSb alloys by NH4OH, H2SO4, and H3PO4 based solutions. NH4OH based solutions resulted in smooth surface, while other solutions created rougher and granular surfaces. The etch rates were found to increase with the Sb content. For GaInNAs, x-ray photoelectron spectroscopy revealed the enrichment of In on the etched surfaces, indicating In or In oxides having a smaller removal rate compared to Ga or Ga oxides. The enrichment of In was associated with smoother surfaces after etching and an enhanced photoluminescence caused by lower surface recombination due to reduced surface state density.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC, Department of Physics and Astronomy, University of Turku, Turun Yliopisto/Turun Biomateriaalikeskus
Contributors: Raappana, M., Polojärvi, V., Aho, A., Mäkelä, J., Aho, T., Tukiainen, A., Laukkanen, P., Guina, M.
Number of pages: 7
Pages: 268-274
Publication date: 15 May 2018
Peer-reviewed: Yes

Publication information

Journal: Corrosion Science
Volume: 136
ISSN (Print): 0010-938X
Ratings: 
  • Scopus rating (2018): CiteScore 6.76 SJR 2.131 SNIP 2.595
Original language: English
ASJC Scopus subject areas: Chemistry(all), Chemical Engineering(all), Materials Science(all)
Keywords: A. Alloy, B. AFM, B. XPS, C. Acid corrosion, C. Alkaline corrosion, C. Passivity

Bibliographical note

EXT="Mäkelä, Jaakko"
EXT="Laukkanen, Pekka"

Source: Scopus
Source-ID: 85044276587

Research output: Contribution to journalArticleScientificpeer-review

Nanofibrillated and bacterial celluloses as renewable piezoelectric sensor materials

Cellulose based nanomaterials, generally known as nanocellulose, are interesting renewable biomaterial which has potential applications for example in material science, electronics and biomedical engineering and diagnostics [1]. Cellulose has a strong ability to form light-weight, highly porous, entangled networks makes nanocellulose suitable as substrate or membrane material for various applications, for example as a material for in supercapacitors in different ways [2, 3, 4]. The piezoelectricity of wood was proposed already in 1950’s [5], but only slightly studied since. Here, we report the experimental evidence of significant piezoelectric activity of different type nanocellulose films. We have studied both wood-based cellulose nanofibril (CNF) films [6] and bacterial nanocellulose (BC) films [7] (see Figure 1), as well as composite of chitosan and cellulose nanocrystals (CNC) [8]. Our results suggest that nanocellulose is a potential bio-based piezoelectric sensor material. [1] R. J. Moon et al., Chemical Society Reviews 40(7), 3941 (2007). [2] S. Tuukkanen, S. Lehtimäki, F. Jahangir, A. P. Eskelinen, D. Lupo, S. Franssila, Proceedings of Electronics System-Integration Technology Conference (ESTC) 1-6 (2014). [3] K. Torvinen, S. Lehtimäki, J. T. Keränen, J. Sievänen, J. Vartiainen, E. Hellén, D. Lupo, S. Tuukkanen, Electronic Materials Letters 11(6), 1040 (2015). [4] J. Virtanen, J. Keskinen, A. Pammo, E. Sarlin, S. Tuukkanen, Cellulose 24(8), 3387 (2017). [5] E. Fukada, J Phys Soc Japan, 10, 149 (1955). [6] S. Rajala, T. Siponkoski, E. Sarlin, M. Mettänen, M. Vuoriluoto, A. Pammo, J. Juuti, O. J. Rojas, S. Franssila, S. Tuukkanen, ACS Applied Materials & Interfaces 8(24), 15607 (2016). [7] R. Mangayil, S. Rajala, A. Pammo, E. Sarlin, J. Luo, V. Santala, M. Karp, S. Tuukkanen, ACS Applied Materials & Interfaces 9(22), 19048 (2017). [8] A. Hänninen, S. Rajala, T. Salpavaara, M. Kellomäki, S. Tuukkanen, Procedia Engineering 168, 1176 (2016).

General information

Publication status: Published
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Sensor Technology and Biomeasurements (STB), Research group: Nanoscale Phenomena and Measurements (NPM)
Contributors: Tuukkanen, S.
Number of pages: 1
Publication date: 14 May 2018
Peer-reviewed: Unknown
Event: Paper presented at Micronano System Workshop, Espoo, Finland.
ASJC Scopus subject areas: Engineering(all), Materials Science(all)
Keywords: nanocellulose, Bacterial cellulose, piezoelectric sensor

Research output: Other conference contributionPaper, poster or abstractScientific

A study of electric transport in n- and p-type modulation-doped GaInNAs/GaAs quantum well structures under a high electric field

We present the results of longitudinal carrier transport under a high electrical field in n- and p-type modulation-doped Ga0.68In0.32NyAs1-y/GaAs (y = 0.009, 0.017) quantum well (QW) structures. Nitrogen composition-dependent drift velocities of electrons are observed to be saturated at and at 77 K for the samples with y = 0.009 and y = 0.017, respectively, while the drift velocities of holes do not saturate but slightly increase at the applied electric field in the range of interest. The hole drift velocity is observed to be higher than the electron drift velocity. The electron mobility exhibits an almost temperature-independent characteristic. On the other hand, the hole mobility exhibits a conventional temperature dependence of modulation-doped QW structures. As the temperature increases, the drift velocity of the electrons exhibits an almost an temperature-insensitive characteristic, but, on the other hand, for holes, drift velocity decreases approximately from 107-106 cm s-1. It is observed that the drift velocities of electrons and holes are N-dependent and suppressed at higher electric fields. Furthermore, experimental results show that there is no evidence of negative differential velocity (NDV) behaviour for both n- and p-type samples. To explore the observed electron and hole drift velocity characteristic at high electric fields, we use a simple theoretical model for carrier transport, which takes into account the effect of non-drifting hot phonons. The mobility mapping technique (comparison method) is used to extract hot hole temperature in order to employ it in the non-drifted phonon distribution and to obtain the drift velocity-electric field curves. Then hot electron temperatures are obtained from the drift velocity-electric field curves as a fit parameter using non-drifted hot phonon dynamics. The analytical model is well-matched to the experimental -E curves, indicating that carrier-hot phonon scattering is the main reason for suppressing the NDV mechanism in GaInNAs/GaAs QW structures with a carrier density higher than 1017 cm-3.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC, Istanbul University
Contributors: Sarcan, F., Mutlu, S., Cokduygulular, E., Donmez, O., Erol, A., Puustinen, J., Guina, M.
Publication date: 4 May 2018
Peer-reviewed: Yes

Publication information

Journal: Semiconductor Science and Technology
Volume: 33
Issue number: 6
Article number: 064003
ISSN (Print): 0268-1242
Ratings: 
  • Scopus rating (2018): CiteScore 2.4 SJR 0.744 SNIP 1.002
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering, Materials Chemistry
Keywords: dilute nitride, GaInNAs, hot phonons, hot-electron and hole temperature, modulation-doped GaInNAs/GaAs quantum well
Source: Scopus
Source-ID: 85048073763

Research output: Contribution to journalArticleScientificpeer-review

Switchable light reflectance in dilute magneto-optical colloids based on nickel ferrite nanowires

Optical properties of diluted narrow band gap magnetic semiconductor nanowire colloids are controlled by modest magnetic fields under 100 Oe. High aspect ratio NiFe2O4 nanowires are used to achieve responsiveness to magnetic field, light absorption and -scattering. Visible light reflectance of the diluted colloids can be either increased or decreased depending on the nanowire alignment relative to the direction of the light propagation. The prepared colloids can be applied as magneto-optical switches or as smart window devices.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Institute of Physics, University of Tartu, Riga Technical University, CRPP, University of Latvia
Contributors: Sutka, A., Timusk, M., Joost, U., Ignatans, R., Maiorov, M.
Number of pages: 3
Pages: 119-121
Publication date: 2 May 2018
Peer-reviewed: Yes

Publication information

Journal: e-Journal of Surface Science and Nanotechnology
Volume: 16
ISSN (Print): 1348-0391
Ratings: 
  • Scopus rating (2018): CiteScore 0.58 SJR 0.216 SNIP 0.337
Original language: English
ASJC Scopus subject areas: Biotechnology, Bioengineering, Condensed Matter Physics, Mechanics of Materials, Surfaces and Interfaces, Surfaces, Coatings and Films
Keywords: Colloid, Ferrimagnetic, Magneto-optical, Nanowire, NiFe2O4

Bibliographical note

INT=fot,"Joost, Urmas"

Source: Scopus
Source-ID: 85047369076

Research output: Contribution to journalArticleScientificpeer-review

Characteristics of nFOG, an aerosol-based wet thin film coating technique

An atmospheric pressure aerosol-based wet thin film coating technique called the nFOG is characterized and applied in polymer film coatings. In the nFOG, a fog of droplets is formed by two air-assist atomizers oriented toward each other inside a deposition chamber. The droplets settle gravitationally and deposit on a substrate, forming a wet film. In this study, the continuous deposition mode of the nFOG is explored. We determined the size distribution of water droplets inside the chamber in a wide side range of 0.1–100 µm and on the substrate using aerosol measurement instruments and optical microscopy, respectively. The droplet size distribution was found to be bimodal with droplets of approximately 30–50 µm contributing the most to the mass of the formed wet film. The complementary measurement methods allow us to estimate the role of different droplet deposition mechanisms. The obtained results suggest that the deposition velocity of the droplets is lower than the calculated terminal settling velocity, likely due to the flow fields inside the chamber. Furthermore, the mass flux of the droplets onto the substrate is determined to be in the order of 1 g/m3s, corresponding to a wet film growth rate of 1 µm/s. Finally, the nFOG technique is demonstrated by preparing polymer films with thicknesses in the range of approximately 0.1–20 µm.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Materials Science, RISE Bioscience and Materials, Research Institutes of Sweden, Lund University
Contributors: Harra, J., Tuominen, M., Juuti, P., Rissler, J., Koivuluoto, H., Haapanen, J., Niemelä-Anttonen, H., Stenroos, C., Teisala, H., Lahti, J., Kuusipalo, J., Vuoristo, P., Mäkelä, J. M.
Number of pages: 10
Pages: 623-632
Publication date: May 2018
Peer-reviewed: Yes
Early online date: 1 Feb 2018

Publication information

Journal: Journal of Coatings Technology Research
Volume: 15
Issue number: 3
ISSN (Print): 1547-0091
Ratings: 
  • Scopus rating (2018): CiteScore 1.66
Original language: English
ASJC Scopus subject areas: Chemistry(all), Surfaces and Interfaces, Surfaces, Coatings and Films, Colloid and Surface Chemistry
Keywords: Aerosol measurement, Droplet size distribution, nFOG, Polymer film, Wet coating technique

Bibliographical note

EXT="Tuominen, Mikko"

Source: Scopus
Source-ID: 85045145179

Research output: Contribution to journalArticleScientificpeer-review

Accurate Binding of Sodium and Calcium to a POPC Bilayer by Effective Inclusion of Electronic Polarization

Binding affinities and stoichiometries of Na+ and Ca2+ ions to phospholipid bilayers are of paramount significance in the properties and functionality of cellular membranes. Current estimates of binding affinities and stoichiometries of cations are, however, inconsistent due to limitations in the available experimental and computational methods. In this work, we improve the description of the binding details of Na+ and Ca2+ ions to a 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayer by implicitly including electronic polarization as a mean field correction, known as the electronic continuum correction (ECC). This is applied by scaling the partial charges of a selected state-of-the-art POPC lipid model for molecular dynamics simulations. Our improved ECC-POPC model reproduces not only the experimentally measured structural parameters for the ion-free membrane, but also the response of lipid headgroup to a strongly bound cationic amphiphile, as well as the binding affinities of Na+ and Ca2+ ions. With our new model, we observe on the one side negligible binding of Na+ ions to POPC bilayer, while on the other side stronger interactions of Ca2+ primarily with phosphate oxygens, which is in agreement with the previous interpretations of the experimental spectroscopic data. The present model results in Ca2+ ions forming complexes with one to three POPC molecules with almost equal probabilities, suggesting more complex binding stoichiometries than those from simple models used to interpret the NMR data previously. The results of this work pave the way to quantitative molecular simulations with realistic electrostatic interactions of complex biochemical systems at cellular membranes.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Biological Physics and Soft Matter, Research area: Computational Physics, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Department of Physical Chemistry, University of Helsinki Institute of Biotechnology
Contributors: Melcr, J., Martinez-Seara, H., Nencini, R., Kolafa, J., Jungwirth, P., Ollila, O. H. S.
Number of pages: 12
Pages: 4546-4557
Publication date: 26 Apr 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry B
Volume: 122
Issue number: 16
ISSN (Print): 1520-6106
Ratings: 
  • Scopus rating (2018): CiteScore 3.03 SJR 1.109 SNIP 0.965
Original language: English
ASJC Scopus subject areas: Physical and Theoretical Chemistry, Surfaces, Coatings and Films, Materials Chemistry

Bibliographical note

EXT=”Martinez-Seara, Hector”
EXT="Ollila, O. H. Samuli"

Source: Scopus
Source-ID: 85046019210

Research output: Contribution to journalArticleScientificpeer-review

Powering of an HTS dipole insert-magnet operated standalone in helium gas between 5 and 85 K

This paper describes the standalone magnet cold testing of the high temperature superconducting (HTS) magnet Feather-M2.1-2. This magnet was constructed within the European funded FP7-EUCARD2 collaboration to test a Roebel type HTS cable, and is one of the first high temperature superconducting dipole magnets in the world. The magnet was operated in forced flow helium gas with temperatures ranging between 5 and 85 K. During the tests a magnetic dipole field of 3.1 T was reached inside the aperture at a current of 6.5 kA and a temperature of 5.7 K. These values are in agreement with the self-field critical current of the used SuperOx cable assembled with Sunam tapes (low-performance batch), thereby confirming that no degradation occurred during winding, impregnation, assembly and cool-down of the magnet. The magnet was quenched many tens of times by ramping over the critical current and no degradation nor training was evident. During the tests the voltage over the coil was monitored in the microvolt range. An inductive cancellation wire was used to remove the inductive component, thereby significantly reducing noise levels. Close to the quench current, drift was detected both in temperature and voltage over the coil. This drifting happens in a time scale of minutes and is a clear indication that the magnet has reached its limit. All quenches happened approximately at the same average electric field and thus none of the quenches occurred unexpectedly.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, European Organization for Nuclear Research, University of Twente, French Atomic Energy Commission (CEA) Saclay, Karlsruhe Institute of Technology, Insitute for Technical Physics, Germany, SuperOx, Victoria University of Wellington, Bruker HTS, University of Southampton
Contributors: Nugteren, J. V., Kirby, G., Bajas, H., Bajko, M., Ballarino, A., Bottura, L., Chiuchiolo, A., Contat, P. A., Dhallé, M., Durante, M., Fazilleau, P., Fontalva, A., Gao, P., Goldacker, W., Kate, H. T., Kario, A., Lahtinen, V., Lorin, C., Markelov, A., Mazet, J., Molodyk, A., Murtomäki, J., Long, N., Perez, J., Petrone, C., Pincot, F., Rijk, G. D., Rossi, L., Russenschuck, S., Ruuskanen, J., Schmitz, K., Stenvall, A., Usoskin, A., Willering, G., Yang, Y.
Publication date: 25 Apr 2018
Peer-reviewed: Yes

Publication information

Journal: Superconductor Science and Technology
Volume: 31
Issue number: 6
Article number: 065002
ISSN (Print): 0953-2048
Ratings: 
  • Scopus rating (2018): CiteScore 2.59 SJR 0.879 SNIP 1.344
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Condensed Matter Physics, Metals and Alloys, Electrical and Electronic Engineering, Materials Chemistry
Keywords: cold testing, high temperature superconductors, superconducting accelerator magnets, superconducting magnets

Bibliographical note

EXT="Murtomäki, J."

Source: Scopus
Source-ID: 85046942716

Research output: Contribution to journalArticleScientificpeer-review

Quantum-well Laser Emitting at 1.2 μm-1.3 μm Window Monolithically Integrated on Ge Substrate

We report a quantum-well laser diode monolithically integrated on Ge substrate. The gain is provided by two GaInNAsSb/GaAs quantum-wells with emission at 1.2 μm-1.3 μm. The diode exhibits continuous-wave operation with mW-level output power at room temperature.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Photonics, Research group: ORC
Contributors: Guina, M., Isoaho, R., Viheriälä, J., Aho, A., Aho, A., Tukiainen, A.
Number of pages: 3
Pages: 1-3
Publication date: 24 Apr 2018

Host publication information

Title of host publication: 43rd European Conference on Optical Communication, ECOC 2017
Publisher: IEEE
ISBN (Electronic): 9781538656242
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Source: Scopus
Source-ID: 85046978554

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Composite Hydrogels Using Bioinspired Approach with in Situ Fast Gelation and Self-Healing Ability as Future Injectable Biomaterial

Biopolymers are attractive candidates to fabricate biocompatible hydrogels, but the low water solubility of most of them at physiological pH has hindered their applications. To prepare a water-soluble derivative of chitosan (WSC) biopolymer, it was grafted with a small anionic amino acid, l-glutamic acid, using a single-step 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide coupling reaction. This resulted in a zwitterion-tethered structure onto the polymer backbone. The degree of substitution range was 13–16 ± 1.25%, which was controlled by varying the feeding reagent ratios. Differential scanning calorimetry- and X-ray diffraction-based analysis confirmed a transition from amorphous into a moderately amorphous/crystalline morphology after amino acid grafting, which made the derivative water-soluble at physiological pH. Composite hydrogels gelated within 60 s when using this WSC together with benzaldehyde-terminated 4-arm poly(ethylene glycol) as cross-linker. The compressive modulus of these hydrogels could be easily tuned between 4.0 ± 1.0 and 31 ± 2.5 kPa, either by changing the cross-linker concentration or total solid content in the final gel. The gels were injectable at the lowest cross-linker as well as total solid content, due to the enhanced elastic behavior. These hydrogels showed biodegradability during a 1 month incubation period in phosphate-buffered saline with weight remaining of 60 ± 1.5 and 44 ± 1.45% at pHs 7.4 and 6.5, respectively. The cytocompatibility of the gels was tested using the fibroblast cell line (i.e., WI-38), which showed good cell viability on the gel surface. Therefore, these hydrogels could be an important injectable biomaterial for delivery purpose in the future.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Faculty of Biomedical Sciences and Engineering, Chemistry and Bioengineering, Materials Science, Research group: Biomaterials and Tissue Engineering Group, BioMediTech, Institute of Chemical Sciences, 25120 Peshawar, Pakistan
Contributors: Khan, M., Koivisto, J., Hukka, T., Hokka, M., Kellomäki, M.
Pages: 11950-11960
Publication date: 11 Apr 2018
Peer-reviewed: Yes
Early online date: 15 Mar 2018

Publication information

Journal: ACS Applied Materials & Interfaces
Volume: 10
Issue number: 14
ISSN (Print): 1944-8244
Ratings: 
  • Scopus rating (2018): CiteScore 8.69 SJR 2.596 SNIP 1.539
Original language: English
ASJC Scopus subject areas: Materials Science(all), Chemistry(all)

Research output: Contribution to journalArticleScientificpeer-review

Membrane bound COMT isoform is an interfacial enzyme: General mechanism and new drug design paradigm

The enzyme catechol-O-methyltransferase (COMT) has water soluble (S-COMT) and membrane associated (MB-COMT), bitopic, isoforms. Of these MB-COMT is a drug target in relation to the treatment of Parkinson's disease. Using a combination of computational and experimental protocols, we have determined the substrate selection mechanism specific to MB-COMT. We show: (1) substrates with preferred affinity for MB-COMT over S-COMT orient in the membrane in a fashion conducive to catalysis from the membrane surface and (2) binding of COMT to its cofactor ADOMET induces conformational change that drives the catalytic surface of the protein to the membrane surface, where the substrates and Mg2+ ions, required for catalysis, are found. Bioinformatics analysis reveals evidence of this mechanism in other proteins, including several existing drug targets. The development of new COMT inhibitors with preferential affinity for MB-COMT over S-COMT is now possible and insight of broader relevance, into the function of bitopic enzymes, is provided.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Universite de Geneve
Contributors: Magarkar, A., Parkkila, P., Viitala, T., Lajunen, T., Mobarak, E., Licari, G., Cramariuc, O., Vauthey, E., Róg, T., Bunker, A.
Number of pages: 4
Pages: 3440-3443
Publication date: 11 Apr 2018
Peer-reviewed: Yes

Publication information

Journal: Chemical Communications
Volume: 54
Issue number: 28
ISSN (Print): 1359-7345
Ratings: 
  • Scopus rating (2018): CiteScore 6.12 SJR 2.177 SNIP 1.133
Original language: English
ASJC Scopus subject areas: Catalysis, Electronic, Optical and Magnetic Materials, Ceramics and Composites, Chemistry(all), Surfaces, Coatings and Films, Metals and Alloys, Materials Chemistry
Source: Scopus
Source-ID: 85044968200

Research output: Contribution to journalArticleScientificpeer-review

Non-intersecting leaf insertion algorithm for tree structure models

We present an algorithm and an implementation to insert broadleaves or needleleaves into a quantitative structure model according to an arbitrary distribution, and a data structure to store the required information efficiently. A structure model contains the geometry and branching structure of a tree. The purpose of this work is to offer a tool for making more realistic simulations of tree models with leaves, particularly for tree models developed from terrestrial laser scanning (TLS) measurements. We demonstrate leaf insertion using cylinder-based structure models, but the associated software implementation is written in a way that enables the easy use of other types of structure models. Distributions controlling leaf location, size and angles as well as the shape of individual leaves are user definable, allowing any type of distribution. The leaf generation process consist of two stages, the first of which generates individual leaf geometry following the input distributions, while in the other stage intersections are prevented by carrying out transformations when required. Initial testing was carried out on English oak trees to demonstrate the approach and to assess the required computational resources. Depending on the size and complexity of the tree, leaf generation takes between 6 and 18 min. Various leaf area density distributions were defined, and the resulting leaf covers were compared with manual leaf harvesting measurements. The results are not conclusive, but they show great potential for the method. In the future, if our method is demonstrated to work well for TLS data from multiple tree types, the approach is likely to be very useful for three-dimensional structure and radiative transfer simulation applications, including remote sensing, ecology and forestry, among others.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Mathematics, Forest Research, Department of Applied Health Research, NERC National Centre for Earth Observation (NCEO), University of Salford, Newcastle University, United Kingdom, York St John University
Contributors: Åkerblom, M., Raumonen, P., Casella, E., Disney, M. I., Danson, F. M., Gaulton, R., Schofield, L. A., Kaasalainen, M.
Publication date: 6 Apr 2018
Peer-reviewed: Yes

Publication information

Journal: Interface Focus
Volume: 8
Issue number: 2
Article number: 20170045
ISSN (Print): 2042-8898
Ratings: 
  • Scopus rating (2018): CiteScore 2.97 SJR 1.138 SNIP 0.939
Original language: English
ASJC Scopus subject areas: Biotechnology, Biophysics, Bioengineering, Biochemistry, Biomaterials, Biomedical Engineering
Keywords: Laser scanning, Leaf distribution, Leaf insertion, Quantitative structure model, Tree reconstruction
Electronic versions: 
Source: Scopus
Source-ID: 85043466694

Research output: Contribution to journalArticleScientificpeer-review

Uncertainty in multispectral lidar signals caused by incidence angle effects

Multispectral terrestrial laser scanning (TLS) is an emerging technology. Several manufacturers already offer commercial dual or three wavelength airborne laser scanners, while multispectral TLS is still carried out mainly with research instruments. Many of these research efforts have focused on the study of vegetation. The aim of this paper is to study the uncertainty of the measurement of spectral indices of vegetation with multispectral lidar. Using two spectral indices as examples, we find that the uncertainty is due to systematic errors caused by the wavelength dependency of laser incidence angle effects. This finding is empirical, and the error cannot be removed by modelling or instrument modification. The discovery and study of these effects has been enabled by hyperspectral and multispectral TLS, and it has become a subject of active research within the past few years. We summarize the most recent studies on multi-wavelength incidence angle effects and present new results on the effect of specular reflection from the leaf surface, and the surface structure, which have been suggested to play a key role. We also discuss the consequences to the measurement of spectral indices with multispectral TLS, and a possible correction scheme using a synthetic laser footprint.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Mathematics, Department of Navigation and Positioning, FGI
Contributors: Kaasalainen, S., Åkerblom, M., Nevalainen, O., Hakala, T., Kaasalainen, M.
Publication date: 6 Apr 2018
Peer-reviewed: Yes

Publication information

Journal: Interface Focus
Volume: 8
Issue number: 2
Article number: 20170033
ISSN (Print): 2042-8898
Ratings: 
  • Scopus rating (2018): CiteScore 2.97 SJR 1.138 SNIP 0.939
Original language: English
ASJC Scopus subject areas: Biotechnology, Biophysics, Bioengineering, Biochemistry, Biomaterials, Biomedical Engineering
Keywords: Hyperspectral, Incidence angle, Laser scanning, Vegetation
Electronic versions: 
Source: Scopus
Source-ID: 85043458754

Research output: Contribution to journalArticleScientificpeer-review

Weighing trees with lasers: Advances, challenges and opportunities

Terrestrial laser scanning (TLS) is providing exciting new ways to quantify tree and forest structure, particularly above-ground biomass (AGB). We show how TLS can address some of the key uncertainties and limitations of current approaches to estimating AGB based on empirical allometric scaling equations (ASEs) that underpin all large-scale estimates of AGB. TLS provides extremely detailed non-destructive measurements of tree form independent of tree size and shape. We show examples of three-dimensional (3D) TLS measurements from various tropical and temperate forests and describe how the resulting TLS point clouds can be used to produce quantitative 3D models of branch and trunk size, shape and distribution. These models can drastically improve estimates of AGB, provide new, improved large-scale ASEs, and deliver insights into a range of fundamental tree properties related to structure. Large quantities of detailed measurements of individual 3D tree structure also have the potential to open new and exciting avenues of research in areas where difficulties of measurement have until now prevented statistical approaches to detecting and understanding underlying patterns of scaling, form and function. We discuss these opportunities and some of the challenges that remain to be overcome to enable wider adoption of TLS methods.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Mathematics, Department of Applied Health Research, NERC National Centre for Earth Observation (NCEO), National Physical Laboratory, Universiteit Gent, School of Geography, University of Leeds
Contributors: Disney, M. I., Boni Vicari, M., Burt, A., Calders, K., Lewis, S. L., Raumonen, P., Wilkes, P.
Publication date: 6 Apr 2018
Peer-reviewed: Yes

Publication information

Journal: Interface Focus
Volume: 8
Issue number: 2
Article number: 20170048
ISSN (Print): 2042-8898
Ratings: 
  • Scopus rating (2018): CiteScore 2.97 SJR 1.138 SNIP 0.939
Original language: English
ASJC Scopus subject areas: Biotechnology, Biophysics, Bioengineering, Biochemistry, Biomaterials, Biomedical Engineering
Keywords: Above-ground biomass, Buttress, Canopy, Lidar, Structure, Terrestrial laser scanning
Electronic versions: 

Bibliographical note

EXT="Lewis, S. L."

Source: Scopus
Source-ID: 85043466280

Research output: Contribution to journalArticleScientificpeer-review

Effect of nozzle geometry on the microstructure and properties of hvaf-sprayed wc-10co4cr and cr3c2-25nicr coatings

Thermally sprayed hard metal coatings are the industrial standard solution for numerous demanding applications to improve wear resistance. In the aim of improving coating quality by utilising finer particle size distributions, several approaches have been studied to control the spray temperature. The most viable solution is to use the modern high velocity air-fuel (HVAF) spray process, which has already proven to produce high-quality coatings with dense structures. In HVAF spray process, the particle heating and acceleration can be efficiently controlled by changing the nozzle geometry. In this study, fine WC-10Co4Cr and Cr3C2-25NiCr powders were sprayed with three nozzle geometries to investigate their effect on the particle temperature, velocity and coating microstructure. The study demonstrates that the particle melting and resulting carbide dissolution can be efficiently controlled by changing the nozzle geometry from cylindrical to convergent–divergent. Moreover, the average particle velocity was increased from 780 to over 900 m/s. The increase in particle velocity significantly improved the coating structure and density. Further evaluation was carried out to resolve the effect of particle in-flight parameters on coating structure and cavitation erosion resistance, which was significantly improved in the case of WC-10Co4Cr coatings with the increasing average particle velocity.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Surface Engineering, VZÚ Plzeň - Research and Testing Institute, University of West Bohemia
Contributors: Matikainen, V., Koivuluoto, H., Vuoristo, P., Schubert, J., Houdková
Number of pages: 15
Pages: 680-694
Publication date: 1 Apr 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Thermal Spray Technology
Volume: 27
Issue number: 4
ISSN (Print): 1059-9630
Ratings: 
  • Scopus rating (2018): CiteScore 2.3 SJR 0.694 SNIP 1.087
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Surfaces, Coatings and Films, Materials Chemistry
Keywords: cavitation erosion < properties, chromium carbide < feedstock, diagnostics < processing, HP/HVOF < processing, HVAF < processing, HVOF < processing, WC-CO-Cr < feedstock
Source: Scopus
Source-ID: 85045088095

Research output: Contribution to journalArticleScientificpeer-review

Graphene-based tunable plasmon induced transparency in gold strips

Plasmon induced transparency (PIT) has been numerically investigated and experimentally realized by two parallel gold strips on graphene for the mid-infrared (MIR) range. The PIT response is realized by the weak hybridization of two bright modes of the gold strips. The response of the device is adjusted with the lengths of two strips and tuned electrically in real time by changing the Fermi level (Ef) of the graphene. Ef is changed to tune the resonance frequency of the transparency window. A top gating is used to achieve high tunability and a 263 nm shift is obtained by changing the gate voltage from -0.6 V to 2.4 V. The spectral contrast ratio of our devices is up to 82%. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Bilkent University, Department of Electrical and Electronics Engineering, Laboratory of Photonics
Contributors: Habib, M., Rashed, A. R., Ozbay, E., Caglayan, H.
Number of pages: 6
Pages: 1069-1074
Publication date: 1 Apr 2018
Peer-reviewed: Yes

Publication information

Journal: Optical Materials Express
Volume: 8
Issue number: 4
ISSN (Print): 2159-3930
Ratings: 
  • Scopus rating (2018): CiteScore 2.76 SJR 0.886 SNIP 1.018
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials
Keywords: ELECTROMAGNETICALLY INDUCED TRANSPARENCY, SLOW LIGHT, METAMATERIAL, SPECTROSCOPY, RESONATORS, DYNAMICS, ANALOG
Electronic versions: 
Source: Scopus
Source-ID: 85044841180

Research output: Contribution to journalArticleScientificpeer-review

Optimization of an E3SPreSSO Energy-Extraction System for High-Field Superconducting Magnets

High-temperature superconducting magnets (HTS) suffer from slow quench propagation and have in large fraction high thermal margin. Due to the high thermal margin, quench protection systems (QPS) based on initiating large normal zones, with, e.g., quench protection heaters or CLIQ, are not effective with HTS, and energy extraction is needed. In large magnets, energy extraction with a single dump is not effective and new solutions are looked for. Recently, a concept E 3SPreSSO for HTS magnet protection has been presented in the scope of European project EuCARD-2. E 3 SPreSSO utilizes a series-connected bifilar HTS or LTS coil. In this work, we present a methodology to design QPS based on E 3 SPreSSO for HTS magnets. Then, we utilize this methodology to design and analyze the suitability of such QPS for a 20 T HTS accelerator dipole.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering
Contributors: Ruuskanen, J., Stenvall, A., Van Nugteren, J., Lahtinen, V.
Publication date: 1 Apr 2018
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 28
Issue number: 3
Article number: 4700805
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2018): CiteScore 1.65 SJR 0.406 SNIP 0.969
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Accelerator magnets, HTS cables, modeling, quench protection

Bibliographical note

INT=eee,"Van Nugteren, Jeroen"

Source: Scopus
Source-ID: 85041649824

Research output: Contribution to journalArticleScientificpeer-review

Hydrazone crosslinked hyaluronan-based hydrogels for therapeutic delivery of adipose stem cells to treat corneal defects

Corneal blindness is a worldwide problem, plagued by insufficient amount of high-quality donor tissue. Cell therapy using human adipose stem cells (hASCs) has risen as an alternative to regenerate damaged corneal stromal tissue, the main structural and refractive layer of the cornea. Herein we propose a method to deliver hASCs into corneal defects in hyaluronan (HA)-based hydrogels, which form rapidly in situ by hydrazone crosslinking. We fabricated two different HA-based hydrazone-crosslinked hydrogels (HALD1-HACDH and HALD2-HAADH), and characterized their swelling, degradation, mechanical, rheological and optical properties and their ability to support hASC survival. To promote hASC attachment and survival, we incorporated collagen I (col I) to the more stable HALD1-HACDH hydrogel, since the HALD2-HAADH hydrogel suffered swift degradation in culture conditions. We then used an organ culture model with excised porcine corneas to study the delivery of hASCs in these three hydrogels for stromal defect repair. Although all hydrogels showed good hASC survival directly after encapsulation, only the collagen-containing HALD1-HACDH-col I hydrogel showed cells with elongated morphology, and significantly higher cell metabolic activity than the HALD1-HACDH gel. The addition of col I also increased the stiffness and reduced the swelling ratio of the resulting hydrogel. Most importantly, the corneal organ culture model demonstrated these hydrogels as clinically feasible cell delivery vehicles to corneal defects, allowing efficient hASC integration to the corneal stroma and overgrowth of corneal epithelial cells.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Faculty of Biomedical Sciences and Engineering, Materials Science, Research group: Micro and Nanosystems Research Group, Research group: Biomaterials and Tissue Engineering Group, BioMediTech Institute and Faculty of Medicine and Life Sciences, BioMediTech Institute and Faculty of Biomedical Sciences and Engineering
Contributors: Koivusalo, L., Karvinen, J., Sorsa, E., Jönkkäri, I., Väliaho, J., Kallio, P., Ilmarinen, T., Miettinen, S., Skottman, H., Kellomäki, M.
Number of pages: 11
Pages: 68-78
Publication date: Apr 2018
Peer-reviewed: Yes
Early online date: 18 Dec 2017

Publication information

Journal: Materials Science and Engineering C
Volume: 85
ISSN (Print): 0928-4931
Ratings: 
  • Scopus rating (2018): CiteScore 5.07 SJR 1.149 SNIP 1.344
Original language: English
ASJC Scopus subject areas: Materials Science(all), Condensed Matter Physics, Mechanics of Materials, Mechanical Engineering
Keywords: Adipose stem cells, Cell delivery, Collagen I, Corneal stroma, Hyaluronan, Hydrogel

Bibliographical note

INT=tut-bmt,"Sorsa, Eetu"

Source: Scopus
Source-ID: 85038877709

Research output: Contribution to journalArticleScientificpeer-review

The EuCARD2 Future Magnets Program for particle accelerator high field dipoles: review of results and next steps

The EuCARD2 collaboration aims at the development of a 10 kA-class superconducting, high current density cable suitable for accelerator magnets, to be tested in small coils and magnets capable to deliver 3-5 T when energized in stand-alone mode, and 15-18 T when inserted in a 12-13 T background magnet. REBCO tape, assembled in a Roebel cable, was selected as conductor. The developed REBCO tape has reached a record engineering critical current density, at 4.2 K and 18 T of 956 A/mm2. Roebel cable carried up to 13 kA at 20K when tested in a small coil (FeatherM0.4). Then a first dipole magnet, wound with two low grade Roebel cables of 25 m each, was assembled and tested. The dipole reached the short sample critical current of 6 kA generating more than 3 T central field at about 5.7 K, with indications of good current transfer among cable strands and of relatively soft transition. The construction of a costheta dipole is also discussed. Eucard2 is reaching its objective and is continuing with the H2020-ARIES program aiming at doubling the Je at 20 T to obtain 6 T as standalone and 18 T as insert in a high field facility.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, European Organization for Nuclear Research, CNRS Centre National de la Recherche Scientifique, Universite de Geneve, Istituto Nazionale Di Fisica Nucleare, Frascati, University of Twente, IRFM, Institut de Recherche sur les Lois Fondamentales de l'Univers, Karlsruhe Institute of Technology, Insitute for Technical Physics, Germany, Karlsruhe Institute for Technology, Geneva University Hospital, Institut NÉEL, University of Southampton, United Kingdom, Danish Technological Institute
Contributors: Rossi, L., Badel, A., Bajas, H., Bajko, M., Ballarino, A., Barth, C., Betz, U., Bottura, L., Broggi, F., Chiuchiolo, A., Dhalle, M., Durante, M., Fazilleau, P., Fleiter, J., Gao, P., Goldacker, W., Kario, A., Kirby, G., Lorin, C., Murtomaeki, J. S., van Nugteren, J., Petrone, C., DeRijk, G., Senatore, C., Statera, M., Stenvall, A., Tixador, P., Yang, Y., Usoskin, A., Zangenberg, N.
Publication date: Apr 2018
Peer-reviewed: Yes
Early online date: 22 Dec 2017

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 28
Issue number: 3
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2018): CiteScore 1.65 SJR 0.406 SNIP 0.969
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Accelerator Magnets, Coils, Collaboration, Conductors, Critical current density (superconductivity), High-temperature superconductors, HTS conductor, HTS dipoles, Superconducting magnets
Source: Scopus
Source-ID: 85039777831

Research output: Contribution to journalArticleScientificpeer-review

Online quality evaluation of tissue paper structure on new generation tissue machines

At present, the tissue paper manufacturing is mostly based on the dry crepe technology. During the last decade, the manufacturers have introduced new tissue machines concepts that increase the softness, bulk, and absorption capacity. Such machines produce a strong regular three-dimensional (3D) structure to the sheet before the Yankee cylinder. At present, the quality of the 3D structure is not evaluated, or it is evaluated only subjectively at the mill. This is mostly because of the difficulties to separate reliably the regular 3D pattern from other variations. This paper introduces a frequency analysis based method which separates the surface profile variances in tissue paper to the creping, to the regular 3D pattern and to the residual variation. The 3D surface profiles and their variances were determined online with the photometric stereo method. We show that the introduced analysis method evaluates the variance portions reliably and the results are consistent with the visual perception of the 3D surfaces. In one particular product, the regular 3D pattern explains 74 % of total surface variance; the creping explains 10 % and residual variations 16 %. Furthermore, the creping and residual variances are quite stable over time whereas the variance of the regular 3D pattern fluctuates significantly.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Automation and Hydraulic Engineering, Research group: Robotics and Automation, Valmet Technologies Oy
Contributors: Raunio, J., Löyttyniemi, T., Ritala, R.
Number of pages: 9
Pages: 133-141
Publication date: 26 Mar 2018
Peer-reviewed: Yes

Publication information

Journal: Nordic Pulp and Paper Research Journal
Volume: 33
Issue number: 1
ISSN (Print): 0283-2631
Ratings: 
  • Scopus rating (2018): CiteScore 0.92 SJR 0.386 SNIP 0.585
Original language: English
ASJC Scopus subject areas: Forestry, Materials Science(all)
Keywords: frequency analysis, photometric stereo, regular 3D structure, tissue paper
Source: Scopus
Source-ID: 85047979196

Research output: Contribution to journalArticleScientificpeer-review

Properties of HVOF-sprayed Stellite-6 coatings

Stellite-6 coatings were deposited onto AISI 304 stainless steel substrate by gas-fueled HVOF spraying, systematically varying the process parameter settings. By operating the HVOF torch with a fuel-rich mixture, dense coatings (<1% porosity) are produced, containing up to ≈3 vol% oxide inclusions. A substantial amount of a Cr-rich f.c.c. phase is found, mainly produced by quenching of molten lamellae, and distinct from the equilibrium, Co-based f.c.c. solid solution retained in unmelted particles. These coatings exhibit pseudo-passive behavior and survive 5 cycles (100 h) of the Corrodkote test (ASTM B380-97) with no substrate corrosion. Coatings obtained from oxygen-rich mixtures, on the other hand, contain fewer oxide inclusions but also greater porosity, and do not protect the substrate against corrosion. The wear behavior of the coatings is less influenced by deposition conditions. In ball-on-disk dry sliding tests, all coatings exhibit wear rates of 2–3 × 10−5 mm3/(N·m), higher than those reported for bulk or clad Stellite, because of interlamellar delamination. Strain-induced, “martensitic” phase transformation from the f.c.c. structure to a h.c.p. one is observed over a 1–2 μm depth below the contact surface. Additional tribo-oxidation is onset when frictional heat dissipation has heated the wear debris enough to trigger its reaction with the environment. Correspondingly, a transition to a regime of higher friction occurs (from ≈0.6 to ≈0.8). At 400 °C, lamellar delamination is suppressed but wear rates rise to 5–8 × 10−5 mm3/(N·m) because of abrasive and adhesive wear. At 800 °C, a dense “glaze” tribofilm is formed by sintered debris particles, firmly bonded to a thermally grown oxide scale on the underlying metal surface. The “glaze” protects the coating, lowering the wear rate to ≈1 × 10−5 mm3/(N·m) and the friction coefficient to <0.45. Under high-stress particle abrasion conditions, wear rates of ≈1 × 10−3 mm3/(N·m) are found.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Materials Characterization, Universita degli Studi di Modena e Reggio Emilia, Il Sentiero International Campus S.r.l., Univ of Oulu, ECOR Research SpA
Contributors: Sassatelli, P., Bolelli, G., Lassinantti Gualtieri, M., Heinonen, E., Honkanen, M., Lusvarghi, L., Manfredini, T., Rigon, R., Vippola, M.
Number of pages: 18
Pages: 45-62
Publication date: 25 Mar 2018
Peer-reviewed: Yes

Publication information

Journal: Surface and Coatings Technology
Volume: 338
ISSN (Print): 0257-8972
Ratings: 
  • Scopus rating (2018): CiteScore 3.44 SJR 0.973 SNIP 1.435
Original language: English
ASJC Scopus subject areas: Chemistry(all), Condensed Matter Physics, Surfaces and Interfaces, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Dry particles abrasion, Electrochemical corrosion test, High velocity oxygen-fuel (HVOF), High-temperature tribology, Sliding wear, Stellite coating
Source: Scopus
Source-ID: 85041473768

Research output: Contribution to journalArticleScientificpeer-review

Thermal Isomerization of Hydroxyazobenzenes as a Platform for Vapor Sensing

Photoisomerization of azobenzene derivatives is a versatile tool for devising light-responsive materials for a broad range of applications in photonics, robotics, microfabrication, and biomaterials science. Some applications rely on fast isomerization kinetics, while for others, bistable azobenzenes are preferred. However, solid-state materials where the isomerization kinetics depends on the environmental conditions have been largely overlooked. Herein, an approach to utilize the environmental sensitivity of isomerization kinetics is developed. It is demonstrated that thin polymer films containing hydroxyazobenzenes offer a conceptually novel platform for sensing hydrogen-bonding vapors in the environment. The concept is based on accelerating the thermal cis-trans isomerization rate through hydrogen-bond-catalyzed changes in the thermal isomerization pathway, which allows for devising a relative humidity sensor with high sensitivity and quick response to relative humidity changes. The approach is also applicable for detecting other hydrogen-bonding vapors such as methanol and ethanol. Employing isomerization kinetics of azobenzenes for vapor sensing opens new intriguing possibilities for using azobenzene molecules in the future.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Aalto University
Contributors: Poutanen, M., Ahmed, Z., Rautkari, L., Ikkala, O., Priimägi, A.
Number of pages: 6
Pages: 381-386
Publication date: 20 Mar 2018
Peer-reviewed: Yes

Publication information

Journal: ACS Macro Letters
Volume: 7
Issue number: 3
ISSN (Print): 2161-1653
Ratings: 
  • Scopus rating (2018): CiteScore 5.82 SJR 2.201 SNIP 1.255
Original language: English
ASJC Scopus subject areas: Organic Chemistry, Polymers and Plastics, Inorganic Chemistry, Materials Chemistry
Source: Scopus
Source-ID: 85044222959

Research output: Contribution to journalArticleScientificpeer-review

Improving the high temperature abrasion resistance of thermally sprayed Cr3C2-NiCr coatings by WC addition

Two experimental agglomerated and sintered (a&s) feedstock powders were prepared, in order to reveal the role of WC addition on the microstructure, hardness, and the abrasion resistance of HVOF-sprayed Cr3C2-NiCr coatings. These powders contained 10 wt.% of sub-micron WC, 20 or 10 wt.% of nickel binder, and Cr3C2 as balance. Experimental coatings were deposited by a liquid fueled high velocity oxygen-fuel (HVOF) spray process and subsequently heat treated at 800 °C for 8 h to simulate elevated temperature service conditions. The microstructures of the powders and coatings were studied by SEM and X-ray diffraction, and the hardnesses of coatings were probed by means of micro and nanoindentation. In addition, the high stress abrasion resistance was tested in a temperature range from room temperature up to 800 °C. The microstructural characterization of the coatings displayed the presence of WC and tungsten containing Cr3C2 grains. The coating hardness increased after heat treatment, which stemmed from precipitation of secondary carbides and solid solution strengthening of the binder by tungsten. In addition, the study revealed that both experimental coatings have high wear resistance at room and elevated temperatures.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Surface Engineering, Viktor-Kaplan-Straße 2/C, Fraunhofer Institut für Keramische Technologien und Systeme, Fraunhofer Institut für Werkstoff- und Strahltechnik, Treibacher Industrie AG
Contributors: Janka, L., Berger, L. M., Norpoth, J., Trache, R., Thiele, S., Tomastik, C., Matikainen, V., Vuoristo, P.
Number of pages: 10
Pages: 296-305
Publication date: 15 Mar 2018
Peer-reviewed: Yes

Publication information

Journal: Surface and Coatings Technology
Volume: 337
ISSN (Print): 0257-8972
Ratings: 
  • Scopus rating (2018): CiteScore 3.44 SJR 0.973 SNIP 1.435
Original language: English
ASJC Scopus subject areas: Chemistry(all), Condensed Matter Physics, Surfaces and Interfaces, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Abrasive wear, CrC-NiCr, Hardmetal, High temperature, Thermal spray, WC
Source: Scopus
Source-ID: 85041378943

Research output: Contribution to journalArticleScientificpeer-review

Bobbing of Oxysterols: Molecular Mechanism for Translocation of Tail-Oxidized Sterols through Biological Membranes

Translocation of sterols between cellular membrane leaflets is of key importance in membrane organization, dynamics, and signaling. We present a novel translocation mechanism that differs in a unique manner from the established ones. The bobbing mechanism identified here is demonstrated for tail-oxidized sterols, but is expected to be viable for any molecule containing two polar centers at the opposite sides of the molecule. The mechanism renders translocation across a lipid membrane possible without a change in molecular orientation. For tail-oxidized sterols, the bobbing mechanism provides an exceptionally facile means to translocate these signaling molecules across membrane structures and may thus represent an important pathway in the course of their biological action.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, University of Helsinki, J. Heyrovský Institute of Physical Chemistry, Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, MEMPHYS-Center for Biomembrane Physics, Laboratory of Physics
Contributors: Kulig, W., Mikkolainen, H., Olżyńska, A., Jurkiewicz, P., Cwiklik, L., Hof, M., Vattulainen, I., Jungwirth, P., Rog, T.
Number of pages: 6
Pages: 1118-1123
Publication date: 1 Mar 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry Letters
Volume: 9
Issue number: 5
ISSN (Print): 1948-7185
Ratings: 
  • Scopus rating (2018): CiteScore 7.91 SJR 3.618 SNIP 1.476
Original language: English
ASJC Scopus subject areas: Materials Science(all)

Bibliographical note

INT=fys,"Mikkolainen, Heikki"
EXT="Cwiklik, Lukasz"

Source: Scopus
Source-ID: 85042702390

Research output: Contribution to journalArticleScientificpeer-review

High-performance elastomeric strain sensors based on nanostructured carbon fillers for potential tire applications

For the development of intelligent vehicle tires, especially for future self-driving cars, suitable strain sensors are mandatory. The design of such a strain sensor must fulfil several criteria, most important of all, it must be easily mounted or implanted into the tire and the elastic nature of the sensors must be synchronized with the deformation behaviour of the tire. To our knowledge, we evaluate for the first time, the piezoresistive characteristics of a composite developed from tire rubber, taking into account the morphology (distribution and dispersion of the fillers), filler network structure, crosslinking density and the stiffness (hardness) of the rubber matrix. We use a commercially available synthetic solution polymerized styrene butadiene rubber (SSBR) which is widely used in modern car tire industries. As the internal structure of the filler particles can rearrange or alter during deformation, it is extremely important to study the piezo-resistive performance with respect to crosslinking density, hardness and modulus of the rubber composites in details. The present paper focusses on the development of strain sensors by exploiting conductive elastomeric composites based on SSBR with conducting carbon fillers like carbon black and carbon nanotubes. The sensors can be stretched to several hundred percent of their original length and a sensitivity could be achieved as much as ∼1000 (gauge factor) in a given strain regime of ∼100%, while maintaining the mechanical robustness. Some of the mechanical properties like tensile strength (∼20 MPa), and modulus at 100% elongation are found to be quite satisfactory indicating the suitability of the materials for real applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Leibniz-Institut für Polymerforschung Dresden E.V., Vodafone Department of Mobile Communications Systems
Contributors: Bhagavatheswaran, E. S., Vaikuntam, S. R., Stöckelhuber, K. W., Wießner, S., Heinrich, G., Das, A.
Number of pages: 9
Pages: 240-248
Publication date: 1 Mar 2018
Peer-reviewed: Yes

Publication information

Journal: Materials Today Communications
Volume: 14
ISSN (Print): 2352-4928
Ratings: 
  • Scopus rating (2018): CiteScore 1.98 SJR 0.462 SNIP 0.686
Original language: English
ASJC Scopus subject areas: Materials Science(all), Mechanics of Materials, Materials Chemistry
Source: Scopus
Source-ID: 85044867652

Research output: Contribution to journalArticleScientificpeer-review

Soft hydrazone crosslinked hyaluronan- and alginate-based hydrogels as 3D supportive matrices for human pluripotent stem cell-derived neuronal cells

Regenerative medicine, especially cell therapy combined with a supportive biomaterial scaffold, is considered to be a potential treatment for various deficits in humans. Here, we have produced and investigated the detailed properties of injectable hydrazone crosslinked hyaluronan-polyvinyl alcohol (HA-PVA) and alginate-polyvinyl alcohol (AL-PVA) hydrogels to be used as a supportive biomaterial for 3D neural cell cultures. To the best of our knowledge, this is the first time the polymerization and properties of hydrazone crosslinked AL-PVA hydrogel have been reported. The effect of the degree of substitution and molecular weight of the polymer components as well as the polymer concentration of the hydrogel on the swelling, degradation and mechanical properties of the hydrogels is reported. Furthermore, we studied the effect of the above parameters on the growth of human pluripotent stem cell-derived neuronal cells. The most neural cell supportive HA-PVA hydrogel was composed of high molecular weight HA component with brain-mimicking mechanical properties and decreased polymer concentration. AL-PVA hydrogel, with stiffness quite similar to brain tissue, was also shown to be similarly supportive. Neuronal spreading and 3D network formation was enhanced inside the softest hydrogels.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Faculty of Biomedical Sciences and Engineering, Research group: Biomaterials and Tissue Engineering Group, BioMediTech Institute and Faculty of Medicine and Life Sciences
Contributors: Karvinen, J., Joki, T., Ylä-Outinen, L., Koivisto, J. T., Narkilahti, S., Kellomäki, M.
Number of pages: 11
Pages: 29-39
Publication date: 1 Mar 2018
Peer-reviewed: Yes

Publication information

Journal: Reactive and Functional Polymers
Volume: 124
ISSN (Print): 1381-5148
Ratings: 
  • Scopus rating (2018): CiteScore 3.21 SJR 0.712 SNIP 0.901
Original language: English
ASJC Scopus subject areas: Chemistry(all), Environmental Chemistry, Biochemistry, Chemical Engineering(all), Polymers and Plastics, Materials Chemistry
Keywords: 3D neuronal culture, Alginate, Hyaluronan, Hydrazone, Hydrogel
Source: Scopus
Source-ID: 85040229275

Research output: Contribution to journalArticleScientificpeer-review

Improved Stability of Atomic Layer Deposited Amorphous TiO2 Photoelectrode Coatings by Thermally Induced Oxygen Defects

Amorphous titanium dioxide (a-TiO2) combined with an electrocatalyst has shown to be a promising coating for stabilizing traditional semiconductor materials used in artificial photosynthesis for efficient photoelectrochemical solar-to-fuel energy conversion. In this study we report a detailed analysis of two methods of modifying an undoped thin film of atomic layer deposited (ALD) a-TiO2 without an electrocatalyst to affect its performance in water splitting reaction as a protective photoelectrode coating. The methods are high-temperature annealing in ultrahigh vacuum and atomic hydrogen exposure. A key feature in both methods is that they preserve the amorphous structure of the film. Special attention is paid to the changes in the molecular and electronic structure of a-TiO2 induced by these treatments. On the basis of the photoelectrochemical results, the a-TiO2 is susceptible to photocorrosion but significant improvement in stability is achieved after heat treatment in vacuum at temperatures above 500 °C. On the other hand, the hydrogen treatment does not increase the stability despite the ostensibly similar reduction of a-TiO2. The surface analysis allows us to interpret the improved stability to the thermally induced formation of O- species within a-TiO2 that are essentially electronic defects in the anionic framework.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Materials Science
Contributors: Hannula, M., Ali-Löytty, H., Lahtonen, K., Sarlin, E., Saari, J., Valden, M.
Number of pages: 10
Pages: 1199-1208
Publication date: 27 Feb 2018
Peer-reviewed: Yes

Publication information

Journal: Chemistry of Materials
Volume: 30
Issue number: 4
ISSN (Print): 0897-4756
Ratings: 
  • Scopus rating (2018): CiteScore 9.92 SJR 4.224 SNIP 1.769
Original language: English
ASJC Scopus subject areas: Chemistry(all), Chemical Engineering(all), Materials Chemistry
Electronic versions: 
Source: Scopus
Source-ID: 85042704048

Research output: Contribution to journalArticleScientificpeer-review

UV-Blocking Synthetic Biopolymer from Biomass-Based Bifuran Diester and Ethylene Glycol

A furan-based synthetic biopolymer composed of a bifuran monomer and ethylene glycol was synthesized through melt polycondensation, and the resulting polyester was found to have promising thermal and mechanical properties. The bifuran monomer, dimethyl 2,2′-bifuran-5,5′-dicarboxylate, was prepared using a palladium-catalyzed, phosphine ligand-free direct coupling protocol. A titanium-catalyzed polycondensation procedure was found effective at polymerizing the bifuran monomer with ethylene glycol. The prepared bifuran polyester exhibited several intriguing properties including high tensile modulus. In addition, the bifuran monomer furnished the polyester with a relatively high glass transition temperature. Films prepared from the new polyester also had excellent oxygen and water barrier properties, which were found to be superior to those of poly(ethylene terephthalate). Moreover, the novel polyester also has good ultraviolet radiation blocking properties.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Research group: Chemistry & Advanced Materials, University of Oulu, Research Unit of Sustainable Chemistry, P.O. Box 3000, FI-90014 Oulu, University of Oulu, Fibre and Particle Engineering Research Unit, P.O. Box 4300, FI-90014 Oulu
Contributors: Kainulainen, T. P., Sirviö, J. A., Sethi, J., Hukka, T. I., Heiskanen, J. P.
Number of pages: 8
Pages: 1822-1829
Publication date: 21 Feb 2018
Peer-reviewed: Yes
Early online date: 21 Feb 2018

Publication information

Journal: Macromolecules
Volume: 51
Issue number: 5
ISSN (Print): 0024-9297
Ratings: 
  • Scopus rating (2018): CiteScore 5.88 SJR 2.243 SNIP 1.475
Original language: English
ASJC Scopus subject areas: Chemistry(all), Materials Science(all)
Keywords: Biopolymers, Synthesis, Characterization, Thermal analysis, Spectroscopy

Research output: Contribution to journalArticleScientificpeer-review

Entrapped Styrene Butadiene Polymer Chains by Sol-Gel-Derived Silica Nanoparticles with Hierarchical Raspberry Structures

A sol-gel transformation of liquid silica precursor to solid silica particles was carried out in a one-pot synthesis way, where a solution of styrene butadiene elastomer was present. The composites, thus produced, offered remarkable improvements of mechanical and dynamic mechanical performances compared to precipitated silica. The morphological analysis reveals that the alkoxy-based silica particles resemble a raspberry structure when the synthesis of the silica was carried out in the presence of polymer molecules and represent a much more open silica-network structure. However, in the absence of the polymer, the morphology of the silica particles is found to be different. It is envisaged that the special morphology of the in situ synthesized silica particles contributes to the superior reinforcement effects, which are associated with a strong silica-rubber interaction by rubber chains trapped inside the raspberry-like silica aggregates. Therefore, the interfaces are characterized in detail by low-field solid-state 1H NMR spectroscopy, 29Si solid-state NMR spectroscopy, and energy-dispersive X-ray spectroscopy. Low-field 1H NMR-based double-quantum experiments provide a quantitative information about the cross-link density of the silica-filled rubber composites and about the influence of silane coupling agent on the chemical cross-link density of the network and correlates well with equilibrium swelling measurements. The special microstructure of the alkoxy-based silica was found to be associated with the interaction between alkoxy-based silica and rubber chains as a consequence of particle growth in the presence of rubber chains.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Leibniz-Institut für Polymerforschung Dresden E.V., Vodafone Department of Mobile Communications Systems, Martin-Luther-Universität Halle-Wittenberg
Contributors: Vaikuntam, S. R., Stöckelhuber, K. W., Subramani Bhagavatheswaran, E., Wießner, S., Scheler, U., Saalwächter, K., Formanek, P., Heinrich, G., Das, A.
Number of pages: 13
Pages: 2010-2022
Publication date: 15 Feb 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry B
Volume: 122
Issue number: 6
ISSN (Print): 1520-6106
Ratings: 
  • Scopus rating (2018): CiteScore 3.03 SJR 1.109 SNIP 0.965
Original language: English
ASJC Scopus subject areas: Physical and Theoretical Chemistry, Surfaces, Coatings and Films, Materials Chemistry
Source: Scopus
Source-ID: 85042152539

Research output: Contribution to journalArticleScientificpeer-review

Arc-sprayed Fe-based coatings from coredwires for wear and corrosion protection in power engineering

High wear and corrosion of parts lead to an increase in operating costs at thermal power plants. The present paper shows a possible solution to this problem through the arc spraying of protective coatings. Cored wires of the base alloying system Fe-Cr-C were used as a feedstock. Rise of wear- and heat-resistance of the coatings was achieved by additional alloying with Al, B, Ti, and Y. The wear and heat resistance of the coatings were tested via a two-body wear test accompanied by microhardness measurement and the gravimetric method, respectively. A high-temperature corrosion test was performed at 550 °C under KCl salt deposition. The porosity and adhesion strengths of the coatings were also evaluated. The microstructure was investigated with a scanning electron microscope (SEM) unit equipped with an energy dispersive X-ray (EDX) microanalyzer, and the phase composition was assessed by X-ray diffractometry. The test results showed the positive influence of additional alloying with Y on the coating properties. A comparison with commercial boiler materials showed that the coatings have the same level of heat resistance as austenite steels and are an order of magnitude higher than that of pearlite and martensite-ferrite steels. The coatings can be applied to wear- and heat-resistant applications at 20-700 °C.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, B. N. Yeltsin Ural Federal University, Russian Academy of Sciences, Ural Branch of the Russian Academy of Sciences
Contributors: Yury, K., Filippov, M., Makarov, A., Malygina, I., Soboleva, N., Fantozzi, D., Andrea, M., Koivuluoto, H., Vuoristo, P.
Publication date: 1 Feb 2018
Peer-reviewed: Yes

Publication information

Journal: Coatings
Volume: 8
Issue number: 2
Article number: 71
ISSN (Print): 2079-6412
Ratings: 
  • Scopus rating (2018): CiteScore 2.42 SNIP 1.186
Original language: English
ASJC Scopus subject areas: Surfaces, Coatings and Films, Materials Chemistry, Surfaces and Interfaces
Keywords: Adhesion, Arc spraying, Coating, Cored wire, Waste-to-energy boilers, Wear and corrosion resistance
Electronic versions: 
Source: Scopus
Source-ID: 85047907541

Research output: Contribution to journalArticleScientificpeer-review

Azobenzene-based polymers: Emerging applications as cell culture platforms

The fabrication of biomaterials whose properties are activated or inhibited on demand via light is appealing for fundamental biological studies as well as for the development of new applications in tissue engineering and regenerative medicine. One of the most widely used molecules in light-controlled systems is azobenzene for its ability to isomerise in response to light. In this minireview, the fundamental landmarks towards the application of azobenzene-containing materials as cell culture substrates will be highlighted, foreseeing their massive use as next-generation cell-instructive materials.

General information

Publication status: Published
MoE publication type: A2 Review article in a scientific journal
Organisations: Dipartimento di Ingegneria Chimica dei Materiali e della Produzione Industriale, ENEA/CREATE/Università Degli Studi Napoli Federico II, Center for Advanced Biomaterials for Healthcare, Italian Institute of Technology
Contributors: Fedele, C., Netti, P. A., Cavalli, S.
Number of pages: 6
Pages: 990-995
Publication date: Feb 2018
Peer-reviewed: Yes

Publication information

Journal: Biomaterials Science
Volume: 6
Issue number: 5
ISSN (Print): 2047-4830
Ratings: 
  • Scopus rating (2018): CiteScore 5.31 SJR 1.539 SNIP 0.99
Original language: English
ASJC Scopus subject areas: Biomedical Engineering, Materials Science(all)

Bibliographical note

EXT="Fedele, C."

Source: Scopus
Source-ID: 85046293996

Research output: Contribution to journalReview ArticleScientificpeer-review

Controlled Growth of Supported ZnO Inverted Nanopyramids with Downward Pointing Tips

High purity porous ZnO nanopyramids with controllable properties are grown on their tips on Si(100) substrates by means of a catalyst-free vapor phase deposition route in a wet oxygen reaction environment. The system degree of preferential [001] orientation, as well as nanopyramid size, geometrical shape, and density distribution, can be finely tuned by varying the growth temperature between 300 and 400 °C, whereas higher temperatures lead to more compact systems with a three-dimensional (3D) morphology. A growth mechanism of the obtained ZnO nanostructures based on a self-catalytic vapor-solid (VS) mode is proposed, in order to explain the evolution of nanostructure morphologies as a function of the adopted process conditions. The results obtained by a thorough chemico-physical characterization enable us to get an improved control over the properties of ZnO nanopyramids grown by this technique. Taken together, they are of noticeable importance not only for fundamental research on ZnO nanomaterials with controlled nano-organization but also to tailor ZnO functionalities in view of various potential applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Supramolecular photochemistry, Chemistry and Bioengineering, Universita degli Studi di Padova, Italy, Universiteit Antwerpen, VTT Technical Research Centre of Finland
Contributors: Barreca, D., Carraro, G., Maccato, C., Altantzis, T., Kaunisto, K., Gasparotto, A.
Number of pages: 9
Pages: 2579-2587
Publication date: Feb 2018
Peer-reviewed: Yes

Publication information

Journal: Crystal Growth and Design
Volume: 18
Issue number: 4
ISSN (Print): 1528-7483
Ratings: 
  • Scopus rating (2018): CiteScore 4.01 SJR 1.046 SNIP 1.107
Original language: English
ASJC Scopus subject areas: Chemistry(all), Materials Science(all), Condensed Matter Physics
Source: Scopus
Source-ID: 85044992194

Research output: Contribution to journalArticleScientificpeer-review

Temperature scanning stress relaxation of an autonomous self-healing elastomer containing non-covalent reversible network junctions

In this work, we report about the mechanical relaxation characteristics of an intrinsically self-healable imidazole modified commercial rubber. This kind of self-healing rubber was prepared by melt mixing of 1-butyl imidazole with bromo-butyl rubber (bromine modified isoprene-isobutylene copolymer, BIIR). By this melt mixing process, the reactive allylic bromine of bromo-butyl rubber was converted into imidazole bromide salt. The resulting development of an ionic character to the polymer backbone leads to an ionic association of the groups which ultimately results to the formation of a network structure of the rubber chains. The modified BIIR thus behaves like a robust crosslinked rubber and shows unusual self-healing properties. The non-covalent reversible network has been studied in detail with respect to stress relaxation experiments, scanning electron microscopic and X-ray scattering.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Vodafone Department of Mobile Communications Systems, University of Applied Sciences Osnabrück, Leibniz-Institut für Polymerforschung Dresden E.V.
Contributors: Das, A., Sallat, A., Böhme, F., Sarlin, E., Vuorinen, J., Vennemann, N., Heinrich, G., Stöckelhuber, K. W.
Publication date: 19 Jan 2018
Peer-reviewed: Yes

Publication information

Journal: Polymers
Volume: 10
Issue number: 1
Article number: 94
ISSN (Print): 2073-4360
Ratings: 
  • Scopus rating (2018): CiteScore 3.25 SJR 0.724 SNIP 1.057
Original language: English
ASJC Scopus subject areas: Chemistry(all), Polymers and Plastics
Keywords: Bromo-butyl rubber, Ionic modification, Reversible polymer network, Self-healing, Stress-relaxation
Electronic versions: 
Source: Scopus
Source-ID: 85040774453

Research output: Contribution to journalArticleScientificpeer-review

Three-Dimensional Microstructured Azobenzene-Containing Gelatin as a Photoactuable Cell Confining System

In materials science, there is a considerable interest in the fabrication of highly engineered biomaterials that can interact with cells and control their shape. In particular, from the literature, the role played by physical cell confinement in cellular structural organization and thus in the regulation of its functions has been well-established. In this context, the addition of a dynamic feature to physically confining platforms aiming at reproducing in vitro the well-known dynamic interaction between the cells and their microenvironment would be highly desirable. To this aim, we have developed an advanced gelatin-based hydrogel that can be finely micropatterned by two-photon polymerization and stimulated in a controlled way by light irradiation thanks to the presence of an azobenzene cross-linker. Light-triggered expansion of gelatin microstructures induced an in-plane nuclear deformation of physically confined NIH-3T3 cells. The microfabricated photoactuable gelatin shown in this work paves the way to new "dynamic" caging culture systems that can find applications, for example, as "engineered stem cell niches".

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Italian Institute of Technology, ENEA/CREATE/Università Degli Studi Napoli Federico II, Center for Advanced Biomaterials for Healthcare, Dipartimento di Ingegneria Chimica dei Materiali e della Produzione Industriale
Contributors: Pennacchio, F. A., Fedele, C., De Martino, S., Cavalli, S., Vecchione, R., Netti, P. A.
Number of pages: 7
Pages: 91-97
Publication date: 10 Jan 2018
Peer-reviewed: Yes

Publication information

Journal: ACS Applied Materials and Interfaces
Volume: 10
Issue number: 1
ISSN (Print): 1944-8244
Ratings: 
  • Scopus rating (2018): CiteScore 8.69 SJR 2.596 SNIP 1.539
Original language: English
ASJC Scopus subject areas: Materials Science(all)
Keywords: azobenzene, cell confinement, hydrogel, photoactuation, two-photon lithography

Bibliographical note

EXT="Fedele, Chiara"

Source: Scopus
Source-ID: 85040442926

Research output: Contribution to journalArticleScientificpeer-review

Design, synthesis, and structure-property relationships of Er3+ -doped TiO2 luminescent particles synthesized by sol-gel

Titania particles doped with various concentrations of Erbium were synthesized by the sol-gel method followed by different heat treatments. The shape and the grain growth of the particles were noticeably affected by the concentration of Erbium and the heat treatment conditions. An infrared emission at 1530 nm, as well as green and red up-conversion emissions at 550 and 670 nm, were observed under excitation at 976 nm from all of the synthesized particles. The emission spectra and lifetime values appeared to be strongly influenced by the presence of the different crystalline phases. This work presents important guidelines for the synthesis of functional Er3+ -doped titania particles with controlled and tailored spectroscopic properties for photonic applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Photonics Glasses, Politecnico di Torino, Istituto Superiore Mario Boella, CERICOL, nLIGHT Corporation, Centro S3
Contributors: Lopez-Iscoa, P., Pugliese, D., Boetti, N. G., Janner, D., Baldi, G., Petit, L., Milanese, D.
Publication date: 2 Jan 2018
Peer-reviewed: Yes

Publication information

Journal: Nanomaterials
Volume: 8
Issue number: 1
Article number: 20
ISSN (Print): 2079-4991
Ratings: 
  • Scopus rating (2018): CiteScore 4.21 SJR 0.896 SNIP 1.112
Original language: English
ASJC Scopus subject areas: Materials Science(all), Chemical Engineering(all)
Keywords: Erbium-doped titania, Photoluminescence, Sol-gel synthesis
Electronic versions: 
Source: Scopus
Source-ID: 85041603664

Research output: Contribution to journalArticleScientificpeer-review

Multiwavelength surface contouring from phase-coded diffraction patterns

We propose a new algorithm for absolute phase retrieval from multiwavelength noisy phase coded diffraction patterns in the task of surface contouring. A lensless optical setup is considered with a set of successive single wavelength experiments. The phase masks are applied for modulation of the multiwavelength object wavefronts. The algorithm uses the forward and backward propagation for coherent light beams and sparsely encoding wavefronts which leads to the complex-domain block-matching 3D filtering. The key-element of the algorithm is an original aggregation of the multiwavelength object wavefronts for high-dynamic-range profile measurement. Numerical experiments demonstrate that the developed approach leads to the effective solutions explicitly using the sparsity for noise suppression and high-accuracy object profile reconstruction.

General information

Publication status: Published
MoE publication type: A4 Article in a conference publication
Organisations: Signal Processing, Research group: Computational Imaging-CI, ITMO University
Contributors: Katkovnik, V., Shevkunov, I., Petrov, N. V., Eguiazarian, K.
Publication date: 1 Jan 2018

Host publication information

Title of host publication: Unconventional Optical Imaging 2018. Strasbourg, France
Volume: 10677
Publisher: SPIE
Article number: 106771B
ISBN (Print): 978-1-5106-1880-0

Publication series

Name: Proceedings of SPIE - The International Society for Optical Engineering
Volume: 10677
ISSN (Electronic): 0277-786X
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Computer Science Applications, Applied Mathematics, Electrical and Electronic Engineering
Keywords: absolute phase retrieval, discrete optical signal processing, Multiwavelength phase retrieval, phase imaging, surface contouring
Source: Scopus
Source-ID: 85052446644

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Ortho-Fluorination of azophenols increases the mesophase stability of photoresponsive hydrogen-bonded liquid crystals

Photoresponsive liquid crystals (LCs) whose alignment can be controlled with UV-Visible light are appealing for a range of photonic applications. From the perspective of exploring the interplay between the light response and the self-assembly of the molecular components, supramolecular liquid crystals are of particular interest. They allow elaborating the structure-property relationships that govern the optical performance of LC materials by subtle variation of the chemical structures of the building blocks. Herein we present a supramolecular system comprising azophenols and stilbazoles as hydrogen-bond donors and acceptors, respectively, and show that ortho-fluorination of the azophenol dramatically increases the thermal stability of the LC phases, an important characteristics in their further utilization in photonics. The systems exhibit fast photoinduced order-disorder transitions, and rapid recovery of the liquid-crystalline state once the light irradiation is ceased, due to the photochemical properties of azophenols.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Research group: Chemistry & Advanced Materials, University of Duisburg-Essen
Contributors: Saccone, M., Kuntze, K., Ahmed, Z., Siiskonen, A., Giese, M., Priimagi, A.
Number of pages: 6
Pages: 9958-9963
Publication date: 1 Jan 2018
Peer-reviewed: Yes

Publication information

Journal: Journal of Materials Chemistry C
Volume: 6
Issue number: 37
ISSN (Print): 2050-7534
Ratings: 
  • Scopus rating (2018): CiteScore 6.28 SJR 1.885 SNIP 1.321
Original language: English
ASJC Scopus subject areas: Chemistry(all), Materials Chemistry
URLs: 
Source: Scopus
Source-ID: 85054152271

Research output