Precipitate formation in aluminium alloys: Multi-scale modelling approach

Ternary Al–Mg–Si alloys have been modelled based on a multi-scale approach that spans across atomistic and mesoscale models and uses theoretically determined parameters. First, a cluster expansion model for total energy has been trained for atomistic configurations (FCC lattice) based on the data from density functional simulations of electronic structure. Free energy curves as a function of solute (Mg, Si) concentrations and disorder have been obtained by using this parameterisation together with meta-dynamics Monte Carlo sampling. In addition, free energy data, surface tensions as well as strain energy using the linear elasticity theory have been collected to be combined for a mesoscale phase-field model. The application of this approach shows that the formation of a layered MgSi phase, with (100) planes, is a particularly stable solute aggregation motif within the Al host matrix. Moreover, the phase-field model demonstrates that the preferred shape of the MgSi precipitates is needle-like (in FCC), and they can act as precursors for the important and well-known β″-type precipitates which are formed by translating one Mg column by a 1/2 lattice vector. The results provide theoretical evidence that the solute aggregation into needle-like MgSi domains (precipitates) is an inherent property of Al-Mg-Si alloys, and that it takes place even without the presence of vacancies which is a precondition for the eventual formation β″ precipitates.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Materials and Molecular Modeling, Norwegian Univ. of Sci. and Technol.
Contributors: Kleiven, D., Akola, J.
Number of pages: 9
Pages: 123-131
Publication date: 15 Aug 2020
Peer-reviewed: Yes

Publication information

Journal: Acta Materialia
Volume: 195
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: Aluminium alloys, Cluster expansion, Multi-scale modelling, Nucleation, Phase-field
Source: Scopus
Source ID: 85086074670

Research output: Contribution to journalArticleScientificpeer-review

Analytical and Numerical Methods to Estimate the Effective Mechanical Properties of Rutherford Cables

Superconducting Nb3Sn Rutherford cables can be used in the accelerator magnets above 10 T regions that cannot be reached with NbTi. These cables are composed of superconducting multifilamentary strands, interstitial epoxy, and insulation materials. To properly design the magnets made from these cables, it is essential to analyze their mechanical behavior. The prerequisite for this is the knowledge of the mechanical performance of Rutherford cables. In large magnets, these cables cannot be modeled with all details but effective properties and homogenization are typically required. In this work, an analytical model and numerical approach for predicting the effective mechanical properties of Rutherford cables are developed. The analytical model is established on a two-step homogenization and mechanical analysis for composite. The effective mechanical properties of the filament area and the transverse Young's modulus of the strand are first determined by means of utilizing the mechanical theory of the unit cell approach. The composite effective mechanical properties of the strand and interstitial epoxy are homogenized in the first step. The second step homogenization derives the effective mechanical properties of the strands epoxy composite and insulation layers. The numerical approach to determine the effective mechanical properties is based on the finite-element analysis. The developed methodologies are used to obtain the effective mechanical properties of two Nb3Sn Rutherford cables. The influence of the insulation thickness and modulus, the strand's modulus, is studied.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, Lanzhou University
Contributors: Zhao, J., Stenvall, A., Gao, Y., Salmi, T.
Publication date: 1 Aug 2020
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 30
Issue number: 5
Article number: 8400808
ISSN (Print): 1051-8223
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Composite modeling, finite-element analysis (FEA), homogenization, Rutherford cable
Source: Scopus
Source ID: 85080860589

Research output: Contribution to journalArticleScientificpeer-review

Semantics of HTS AC Loss Modeling: Theories, Models, and Experiments

Computer-Assisted modeling is an essential approach to design new devices. It speeds up the process from the initial idea to an actual device and saves resources by reducing the number of built prototypes. This is also a significant practical motivator behind scientific research in contemporary high-Temperature superconductor (HTS) ac loss modeling. However, in the scientific literature in this field, consistent practices about modeling terminology have not been established. Then, it is up to the reader to decide, what is the true intent and meaning of the authors. Consequently, the interpretation of such literature might be very much reader dependent. An inseparable part of the whole modeling process is the development of modeling approaches and numerical methods and comparing the predictions obtained via modeling to experimentally achieved results. It is commonplace to discuss the accuracy of modeling results or the validation of a model. In this article, we discuss the terminology related to theories, models, and experiments in the context of HTS ac loss modeling. We discuss the recursive nature of theories and models in this context, discuss the compatibility of discrete formulations of physics utilized in our field with the corresponding continuum description, and interpret the perceived meaning of validation of a self-consistent model, shedding light on the relationships between theories, models, and measurements. We present our view on understanding these relations in the familiar context of ac losses in HTS, studying case examples through simulations and literature. As a result, we end this article with four conjectures describing our views.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering
Contributors: Lahtinen, V., Stenvall, A.
Publication date: 1 Aug 2020
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 30
Issue number: 5
Article number: 5900809
ISSN (Print): 1051-8223
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: AC losses, experiment, high-Temperature superconductors (HTS), model, modeling, theory
Source: Scopus
Source ID: 85082393173

Research output: Contribution to journalArticleScientificpeer-review

Effect of heat-treatment on the upconversion of NaYF4:Yb3+, Er3+ nanocrystals containing silver phosphate glass

Novel NaYF4:Yb3+, Er3+ nanocrystals containing phosphate glass with composition 83.25NaPO3–9.25NaF-5ZnO-2.5Ag2O (in mol%) was prepared by adding the NaYF4:Yb3+, Er3+ nanocrystals in the glass using the direct doping method. The optical and luminescence properties of this new glass are presented and discussed. The newly developed glass exhibits visible emission under 980 nm pumping with high intensity confirming the presence of the NaYF4:Yb3+, Er3+ nanocrystals in the glass. From the absorption spectrum of the as-prepared glass, it is showed that the as-prepared glasses contains already Ag nanoparticles which are thought to precipitate due to the decomposition of some of the NaYF4:Yb3+, Er3+ nanocrystals occurring during the glass preparation. A heat treatment of the glass was found to lead to the migration of Ag species at the surface of the glass as evidenced using SEM and to a decrease of the intensity of the upconversion mostly due to an increase of the inter defects in the NaYF4:Yb3+, Er3+ nanocrystals due to the heat treatment.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Technical University of Cluj-NapocaUniversitatea Tehnica din Cluj-Napoca
Contributors: Ojha, N., Bogdan, M., Galatus, R., Petit, L.
Publication date: 15 Sep 2020
Peer-reviewed: Yes
Early online date: Jun 2020

Publication information

Journal: Journal of Non-Crystalline Solids
Volume: 544
Article number: 120243
ISSN (Print): 0022-3093
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Condensed Matter Physics, Materials Chemistry
Keywords: Absorption, Luminescence, NaYF:Yb, Er nanocrystals, Phosphate glass, Silver nanoparticles
Source: Scopus
Source ID: 85086450328

Research output: Contribution to journalArticleScientificpeer-review

Hyperspectral phase imaging based on denoising in complex-valued eigensubspace

A novel algorithm for reconstruction of hyperspectral 3D complex domain images (phase/amplitude) from noisy complex domain observations has been developed and studied. This algorithm starts from the SVD (singular value decomposition) analysis of the observed complex-valued data and looks for the optimal low dimension eigenspace. These eigenspace images are processed based on special non-local block-matching complex domain filters. The accuracy and quantitative advantage of the new algorithm for phase and amplitude imaging are demonstrated in simulation tests and in processing of the experimental data. It is shown that the algorithm is effective and provides reliable results even for highly noisy data.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computing Sciences, Research group: Computational Imaging-CI, ITMO University, University of Ulm Medical Center, University of Stuttgart
Contributors: Shevkunov, I., Katkovnik, V., Claus, D., Pedrini, G., Petrov, N. V., Egiazarian, K.
Number of pages: 10
Publication date: 1 Apr 2020
Peer-reviewed: Yes
Early online date: 6 Dec 2019

Publication information

Journal: Optics and Lasers in Engineering
Volume: 127
Article number: 105973
ISSN (Print): 0143-8166
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Mechanical Engineering, Electrical and Electronic Engineering
Keywords: Hyperspectral imaging, Noise filtering, Noise in imaging systems, Phase imaging, Singular value decomposition, Sparse representation
Electronic versions: 
Source: Scopus
Source ID: 85076060273

Research output: Contribution to journalArticleScientificpeer-review

Structure and in vitro dissolution of Mg and Sr containing borosilicate bioactive glasses for bone tissue engineering

Borosilicate bioactive glasses are promising for bone tissue engineering. The objective was to assess the impact of magnesium and/or strontium, when substituted for calcium on the glasses' thermal and dissolution properties. Both Mg and Sr substitution appeared to enhance the hot forming domain, i.e. the ability to hot process (sinter, draw fibres) without adverse crystallization. Structural analysis indicated that substitution of MgO and/or SrO for CaO results in changes in the BO3/BO4 ratio as well as in the ratio between bridging and non-bridging oxygen atoms in the silicate structure. Additionally, a de-shielding effect was noticed when Ca, Mg and Sr are present together in the glass network, possibly owing to PO4 3− charge-balanced preferentially by Na+. The Mg and/or Sr substitution resulted in a lower ion release in simulated body fluid and delayed formation of hydroxyapatite. However, once this layer formed it consisted of a Mg/Sr-substituted apatite. This work highlights the effect of combined ionic substitutions on bioactive glass structure and properties.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Faculty of Biomedical Sciences and Engineering, Friedrich-Schiller-University Jena, Universite de Rennes, CNRS, Centre National de la Recherche Scientifique (CNRS), Universite de Bordeaux - PRES, Lab Bordelais Rech Informat, PICTURA Res Grp, UMR 5800
Contributors: Tainio, J. M., Salazar, D. A., Nommeots-Nomm, A., Roiland, C., Bureau, B., Neuville, D. R., Brauer, D. S., Massera, J.
Publication date: 1 Apr 2020
Peer-reviewed: Yes

Publication information

Journal: Journal of Non-Crystalline Solids
Volume: 533
Article number: 119893
ISSN (Print): 0022-3093
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Condensed Matter Physics, Materials Chemistry
Keywords: Bioactive glasses, Borosilicate glasses, In vitro dissolution, Structural properties, Tissue engineering
Source: Scopus
Source ID: 85078095947

Research output: Contribution to journalArticleScientificpeer-review

High-dimensional quantum gates using full-field spatial modes of photons

Unitary transformations are the fundamental building blocks of gates and operations in quantum information processing, allowing the complete manipulation of quantum systems in a coherent manner. In the case of photons, optical elements that can perform unitary transformations are readily available only for some degrees of freedom, e.g., wave plates for polarization. However, for high-dimensional states encoded in the transverse spatial modes of light, performing arbitrary unitary transformations remains a challenging task for both theoretical proposals and actual implementations. Following the idea of multi-plane light conversion, we show that it is possible to perform a broad variety of unitary operations at high quality by using only a few phase modulation planes. More importantly, we experimentally implement several high-dimensional quantum gates for up to five-dimensional states encoded in the full-field mode structure of photons. In particular, we realize cyclic and quantum Fourier transformations, known as Pauli X -gates and Hadamard Ĥ-gates, respectively, with an average visibility of more than 90%. In addition, we demonstrate near-perfect “unitarity” by means of quantum process tomography, unveiling a process purity of 99%. Last, we demonstrate the benefit of the two independent spatial degrees of freedom, i.e., azimuthal and radial, and implement a two-qubit controlled-NOT quantum operation on a single photon. Thus, our demonstrations open up new paths to implement high-dimensional quantum operations, which can be applied to various tasks in quantum communication, computation, and sensing schemes.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Austrian Academy of Sciences, University of Ottawa, Canada
Contributors: Brandt, F., Hiekkamäki, M., Bouchard, F., Huber, M., Fickler, R.
Number of pages: 10
Pages: 98-107
Publication date: 20 Feb 2020
Peer-reviewed: Yes

Publication information

Journal: Optica
Volume: 7
Issue number: 2
ISSN (Print): 2334-2536
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85079614867

Research output: Contribution to journalArticleScientificpeer-review

Comparative Analysis of Injection Microdisk Lasers Based on InGaAsN Quantum Wells and InAs/InGaAs Quantum Dots

Abstract: The results of comparative analysis of the spectral and threshold characteristics of room-temperature injection microdisk lasers of the spectral range 1.2×× μm with different active regions, notably, InGaAsN/GaAs quantum wells or InAs/InGaAs/GaAs quantum dots are presented. It is found that microlasers of a comparable size with quantum wells possess a larger laser generation threshold when compared with microlasers with quantum dots. At the same time, the latter are characterized by a noticeably smaller fraction of emitted power corresponding to laser modes. The jump to lasing via an excited-state optical transition is also characteristic for them. Microdisk lasers based on InGaAsN alloy do not have these disadvantages.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Russian Academy of Science, St. Petersburg State Polytechnical University, Ioffe Physico-Technical Institute
Contributors: Moiseev, E. I., Maximov, M. V., Kryzhanovskaya, N. V., Simchuk, O. I., Kulagina, M. M., Kadinskaya, S. A., Guina, M., Zhukov, A. E.
Number of pages: 5
Pages: 263-267
Publication date: 1 Feb 2020
Peer-reviewed: Yes

Publication information

Journal: Semiconductors
Volume: 54
Issue number: 2
ISSN (Print): 1063-7826
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Condensed Matter Physics
Keywords: microlaser, nitrogen-containing semiconductors, quantum dots, quantum wells
Source: Scopus
Source ID: 85081636724

Research output: Contribution to journalArticleScientificpeer-review

Superfluid weight and Berezinskii-Kosterlitz-Thouless transition temperature of twisted bilayer graphene

We study superconductivity of twisted bilayer graphene with local and nonlocal attractive interactions. We obtain the superfluid weight and Berezinskii-Kosterlitz-Thouless (BKT) transition temperature for microscopic tight-binding and low-energy continuum models. We predict qualitative differences between local and nonlocal interaction schemes which could be distinguished experimentally. In the flat-band limit where the pair potential exceeds the band width we show that the superfluid weight and BKT temperature are determined by multiband processes and quantum geometry of the band.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Aalto University, University of Jyvaskyla
Contributors: Julku, A., Peltonen, T. J., Liang, L., Heikkilä, T. T., Törmä, P.
Publication date: 1 Feb 2020
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 101
Issue number: 6
Article number: 060505
ISSN (Print): 2469-9950
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics

Bibliographical note

INT=phys,"Liang, L."

Source: Scopus
Source ID: 85082866595

Research output: Contribution to journalArticleScientificpeer-review

Goos-Hänchen and Imbert-Fedorov shifts for epsilon-near-zero materials

We investigate the reflection of a Gaussian beam impinging upon the surface of an epsilon-near-zero (ENZ) medium. In particular, we discuss the occurrence of Goos-Hänchen and Imbert-Fedorov shifts. Our calculations reveal that spatial shifts are significantly enhanced owing to the ENZ nature of the medium, and that their value and angular position can be tuned by tuning the plasma frequency of the medium.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Università dell'Aquila
Contributors: Nieminen, A., Marini, A., Ornigotti, M.
Publication date: 28 Jan 2020
Peer-reviewed: Yes

Publication information

Journal: Journal of Optics
Volume: 22
Issue number: 3
Article number: 035601
ISSN (Print): 2040-8978
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Keywords: beam shifts, Epsilon-near-zero, physical reflection
Source: Scopus
Source ID: 85080149323

Research output: Contribution to journalArticleScientificpeer-review

Plasmon lifetime enhancement in a bright-dark mode coupled system

Metallic nanoparticles can localize the incident light to hot spots as plasmon oscillations, where the intensity can be enhanced by up to four orders of magnitude. Even though the lifetime of plasmons is typically short, it can be increased via interactions with quantum emitters, e.g., spaser nanolasers. However, molecules can bleach in days. Here, we study the lifetime enhancement of plasmon excitations due to the coupling with longer-lifetime dark plasmon modes. We apply an analytical model based on harmonic oscillators to demonstrate that a coupled system of bright and dark plasmon modes decays more slowly than the bright mode alone. Furthermore, exact solutions of the three-dimensional Maxwell equations, i.e., finite-difference time domain, demonstrate that the lifetime of the coupled system significantly increases at the hot spot, which is not predictable by far-field response. The decay of the overall energy of such a coupled system, which can be extracted from experimental absorption measurements, is substantially different from the decay of the hot spot field. This observation enlightens the plasmonic applications in which the hot spot intensity enables the detection of the optical responses.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Hacettepe University, Middle East Technical University
Contributors: Yildiz, B. C., Bek, A., Tasgin, M. E.
Number of pages: 8
Publication date: 16 Jan 2020
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 101
Issue number: 3
Article number: 035416
ISSN (Print): 2469-9950
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 85078332332

Research output: Contribution to journalArticleScientificpeer-review

Transparent Yb3+ doped phosphate glass-ceramics

Yb3+ doped oxyfluorophosphate glasses with the composition (98.75) [90NaPO3-(10-x) Na2O-xNaF] - 1.25Yb2O3 (in mol%) with x = 0, 2.5, 5, 7.5 and 10 were prepared using a standard melting process. The progressive replacement of Na2O by NaF leads to an increase in the number of Q2 units at the expense of the Q1 units. This increase in the polymerization of the glass network leads to a shift of the optical band gap to lower wavelength, to a slight increase in the intensity of the emission at 1000 nm and more importantly to a change in the glass crystallization process. Indeed, both surface and bulk crystallization were observed in the glass with x = 0 while surface crystallization only occurs when NaF is added in the phosphate network. The heat treatment leads to the precipitation of at least three crystalline phases: as x increases, the NaPO3 phase grows at the expense of Na5P3O10. All glasses precipitate the Yb containing crystal, NaYbP2O7 which leads to an increase in the intensity of the emission at 1000 nm compared to the emission at 975 nm. We show for the first time to the best of our knowledge that transparent Yb3+ doped phosphate glass-ceramics can be obtained within this glass system when free of NaF.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Fondazione LINKS – Leading Innovation & Knowledge for Society, CNRS, Université de Bordeaux, ICMCB
Contributors: Hongisto, M., Veber, A., Boetti, N. G., Danto, S., Jubera, V., Petit, L.
Publication date: 1 Jan 2020
Peer-reviewed: Yes

Publication information

Journal: Ceramics International
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: Glass-ceramic, Luminescence, Phosphate glass, XRD, Yb
Source: Scopus
Source ID: 85077933290

Research output: Contribution to journalArticleScientificpeer-review

Sub-microwatt direct laser writing of fluorescent gold nanoclusters in polymer films

We report on the micro-pattering of fluorescent gold nanoclusters embedded in polyvinyl alcohol film using a low-cost continuous-wave laser. We show that the formation of gold nanoclusters requires low-level laser irradiation (<100 W/cm2), corresponding to a sub-microwatt focused beam. This low-intensity requirement enables substantially higher speed and cost-effective light patterning process. As a result of using only small intensities during gold nanoclusters production, no microscopic topological changes were observed in the polymer film. This class of gold nanoclusters potentially finds application in high-speed authenticity marking and similar labeling applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Applied Optics
Contributors: Bitarafan, M. H., Suomala, S., Toivonen, J.
Number of pages: 11
Pages: 138-148
Publication date: 2020
Peer-reviewed: Yes

Publication information

Journal: Optical Materials Express
Volume: 10
Issue number: 1
ISSN (Print): 2159-3930
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials

Bibliographical note

INT=phys,"Bitarafan, Mohammad H."
INT=phys,"Suomala, Sofia"

Source: Scopus
Source ID: 85079045790

Research output: Contribution to journalArticleScientificpeer-review

Full-field mode sorter using two optimized phase transformations for high-dimensional quantum cryptography

High-dimensional encoding schemes have emerged as a novel way to perform quantum information tasks. For high dimensionality, temporal and transverse spatial modes of photons are the two paradigmatic degrees of freedom commonly used in such experiments. Nevertheless, general devices for multi-outcome measurements are still needed to take full advantage of the high-dimensional nature of encoding schemes. We propose a general full-field mode sorting scheme consisting of only up to two optimized phase elements based on evolutionary algorithms that allows for joint sorting of azimuthal and radial modes. We further study the performance of our scheme through simulations in the context of high-dimensional quantum cryptography, where sorting in different mutually unbiased bases and high-fidelity measurement schemes are crucial.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Austrian Academy of Sciences, University of Ottawa, Canada, University of Ulm Medical Center, Centro S3, Max Planck Institute for the Science of Light, Friedrich-Alexander-Universität Erlangen-Nürnberg
Contributors: Fickler, R., Bouchard, F., Giese, E., Grillo, V., Leuchs, G., Karimi, E.
Number of pages: 7
Publication date: 2020
Peer-reviewed: Yes

Publication information

Journal: Journal of Optics (United Kingdom)
Volume: 22
Issue number: 2
Article number: 024001
ISSN (Print): 2040-8978
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Keywords: mode demultiplexing high-dimensional quantum information, quantum cryptography, transverse spatial modes
Electronic versions: 
Source: Scopus
Source ID: 85079689477

Research output: Contribution to journalArticleScientificpeer-review

Electronic transport in n-type modulation-doped AlGaAs/GaAsBi quantum well structures: Influence of Bi and thermal annealing on electron effective mass and electron mobility

We investigate electronic transport properties of as-grown and annealed n-type modulation-doped Al0.15Ga0.85As/GaAs1-xBix (x = 0 and 0.04) quantum well (QW) structures using magnetotransport measurements in the temperature range 4.2 K and 60 K and at magnetic fields up to 18 T. Thermal annealing process was applied at two different temperatures, 700 °C and 350 °C during 60 s and 180 s, respectively. We find that electron effective mass and 2D electron density in as-grown Bi-containing sample are slightly lower than that in Bi-free one. Furthermore, quantum electron mobility and quantum scattering time are observed to be decreased in Bi-containing samples. The annealing process at 700 °C causes a slight increase in electron effective mass and 2D electron density. A negligible decrease in electron effective mass and an increase in 2D electron density are determined following annealing at 350 °C. The observed change in electron effective mass following thermal annealing process is attributed to changing 2D electron density in the samples. No improvement on quantum electron mobility and quantum scattering time are observed following thermal annealing at both process temperatures. We determine that one electron subband (e1) for as-grown and annealed (at 700 °C for 60 s) Bi-containing QWs and two electron subbands (e1 and e2) for the annealed (at 350 °C for 180 s) GaAsBi QW sample and the Bi-free QW sample contribute to electronic transport. Our results reveal that there is no significant direct effect of Bi on effective electron mass, but an indirect effect, in which Bi can provoke changes in 2D electron density and hence causes not to observe actual band-edge electron mass but a deviation from its band-edge value. Therefore, it can be concluded that dispersion curve of conduction band does not change as an effect of Bi incorporation in GaAs.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Istanbul University, Eskişehir Technical University (ESTU), Istanbul University-Cerrahpasa
Contributors: Donmez, O., Aydin, M., Ardali, Yildirim, S., Tiraş, E., Nutku, F., Cetinkaya, C., okduygulular, E., Puustinen, J., Hilska, J., Guina, M., Erol, A.
Publication date: 2020
Peer-reviewed: Yes

Publication information

Journal: Semiconductor Science and Technology
Volume: 35
Issue number: 2
Article number: 025009
ISSN (Print): 0268-1242
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering, Materials Chemistry
Keywords: bismuthindependent effective mass, Electron effective mass in GaAsBi, electron mobility in GaAsBi, electronic transport in GaAsBi, n-type GaAsBi
Source: Scopus
Source ID: 85082305824

Research output: Contribution to journalArticleScientificpeer-review

Hematite Surface Modification toward Efficient Sunlight-Driven Water Splitting Activity: The Role of Gold Nanoparticle Addition

Localized surface plasmon resonance has been investigated to enhance light harvesting in hematite-based photoelectrodes modified with gold nanoparticles (AuNPs); meanwhile, an extensive understanding about the different processes involved in the hematite-AuNP system remains unclear. This work addresses a majority of effects associated with AuNP addition by comparing charge transfer, catalytic and light harvesting efficiencies. The obtained results revealed that the lower AuNP amount leads to a higher photocurrent response of 1.20 mA cm-2 at 1.23 VRHE in comparison with all photoelectrodes designed here. X-ray photoelectron data revealed that hematite photoelectrodes loaded with higher concentrations of AuNPs immersed in an alkaline electrolyte showed hydrated/oxidized gold phase formation at the electrode/electrolyte interface. This change on the semiconductor-metal interface may affect the conductivity impairing the photocatalytic performance because of the passivation layer on the AuNP surface, decreasing the efficiency of charge transfer. Notoriously, increasing AuNP amount supported on the hematite surface clearly promoted higher light absorption, which was surprisingly not followed by photoelectrochemical efficiency. This result suggests here that the plasmon effect is not a dominant phenomenon that drives the photoelectrode performance. In fact, a deeper analysis showed that the loaded hematite photoelectrodes with low amounts of AuNPs provides a Schottky contact at the semiconductor-metal interface leading to Fermi level equilibration enhancing charge transport efficiency, which is classified as the predominant effect leading to higher photoresponse in the system.

General information

Publication status: E-pub ahead of print
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Universidade Federal do ABC, Microscopy Centre
Contributors: Tofanello, A., Freitas, A. L., Carvalho, W. M., Salminen, T., Niemi, T., Souza, F. L.
Publication date: 2020
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry C
ISSN (Print): 1932-7447
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Energy(all), Physical and Theoretical Chemistry, Surfaces, Coatings and Films
Source: Scopus
Source ID: 85082009064

Research output: Contribution to journalArticleScientificpeer-review

Tuneable topological domain wall states in engineered atomic chains

Topological modes in one- and two-dimensional systems have been proposed for numerous applications utilizing their exotic electronic responses. The 1D, zero-energy, topologically protected end modes can be realized in structures implementing the Su–Schrieffer–Heeger (SSH) model. While the edge modes in the SSH model are at exactly the mid-gap energy, other paradigmatic 1D models such as trimer and coupled dimer chains have non-zero energy boundary states. However, these structures have not been realized in an atomically tuneable system that would allow explicit control of the edge modes. Here, we demonstrate atomically controlled trimer and coupled dimer chains realized using chlorine vacancies in the c(2 × 2) adsorption layer on Cu(100). This system allows wide tuneability of the domain wall modes that we experimentally demonstrate using low-temperature scanning tunneling microscopy (STM).

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research area: Computational Physics, Aalto University, Helsinki Institute of Physics, Max-Planck-Institut für Festkörperforschung
Contributors: Huda, M. N., Kezilebieke, S., Ojanen, T., Drost, R., Liljeroth, P.
Number of pages: 5
Publication date: 2020
Peer-reviewed: Yes

Publication information

Journal: npj Quantum Materials
Volume: 5
Issue number: 1
Article number: 17
ISSN (Print): 2397-4648
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 85081728975

Research output: Contribution to journalArticleScientificpeer-review

Improvements in the electromechanical properties of stretchable interconnects by locally tuning the stiffness

Recent advances in materials science and structural design have changed electronic applications from being bulky and rigid objects to small and soft products that have emerged for a wide range of applications, especially human-related products for which mechanical adoption is the key requirement. A typical stretchable application consists of small-sized, rigid IC-chips and passive components interconnected by conductive tracks on soft substrates. The early failure of such devices initiates from the rigid-soft interface due to the accumulation of stress. Therefore, special attention is needed to reduce the strain concentration at the interface. In this paper, stretchable interconnects were fabricated using a screen-printing method and surface mounted devices (SMDs) were bonded using an isotropic conductive adhesive. By partially removing material from the substrate in areas a little way from the rigid components, the stiffness is locally reduced, and this leads to an increase in the local stiffness around the SMDs and hence shields the soft-rigid interface against the stress. Materials can be removed by two different patterns. A finite element analysis and experimental data show 11%-19% improvements in single pull-up tests for the modified samples. This approach makes the electromechanical behaviour independent of encapsulation properties.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, Research group: Wireless Communications and Positioning, Research group: Laboratory for Future Electronics
Contributors: Mosallaei, M., Di Vito, D., Khorramdel, B., Mäntysalo, M.
Publication date: 2020
Peer-reviewed: Yes

Publication information

Journal: Flexible and Printed Electronics
Volume: 5
Issue number: 1
Article number: 015004
ISSN (Print): 2058-8585
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering
Keywords: electromechanical properties, finite element (FE) analysis, printed electronics, screen-printing, strain concentration, stress distribution, stretchable electronics
URLs: 
Source: Scopus
Source ID: 85081953534

Research output: Contribution to journalArticleScientificpeer-review

A Database for Storing Magnet Parameters and Analysis of Quench Test Results in HL-LHC Nb3Sn Short Model Magnets

In recent years, several Nb3Sn high field magnet prototypes have been designed and tested in preparation for the LHC Luminosity upgrade and also for the potential Future Circular Collider (FCC). In this paper we present a Microsoft Excel-based database tool for storing magnet design parameters and results from quench protection tests. The hierarchical and flexible structure of the relational database allows for systematic and coherent analysis of the test data from different magnet assemblies and works as a practical reference for magnet design evolution. Data from quench protection heater tests in several high-field Nb3Sn magnet prototypes has been stored in the database. We use this data to validate the quench simulation assumptions used in FCC 16 T dipole magnet design.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, Research group: Modelling and superconductivity, CERN, European Organization for Nuclear Research (CERN)
Contributors: Salmi, T., Tarhasaari, T., Izquierdo-Bermudez, S.
Number of pages: 5
Publication date: 2020
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 30
Issue number: 4
Article number: 4703705
ISSN (Print): 1051-8223
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: quench protection, quench protection heaters, Superconducting magnets
Source: Scopus
Source ID: 85084795321

Research output: Contribution to journalArticleScientificpeer-review

Novel borosilicate bioactive scaffolds with persistent luminescence

Persistent luminescent amorphous borosilicate scaffolds were successfully prepared, for the first time, with a porosity of >70% using the burn-off technique. The persistent luminescence was obtained by adding the SrAl2O4:Eu2+,Dy3+ microparticles: i) in the glass melt or ii) in the glass crushed into powder prior to the sintering. The scaffolds prepared by adding the microparticles in the glass melt exhibits lower persistent luminescence and a slower reaction rate in simulated body fluid than the scaffolds prepared by adding the microparticles in the glass powder due to the release of strontium from the microparticles into the glass during the glass melting.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Research group: Biomaterials and Tissue Engineering Group, Physics, Research group: Photonics Glasses, Turun yliopisto
Contributors: Del Cerro, P. R., Teittinen, H., Norrbo, I., Lastusaari, M., Massera, J., Petit, L.
Number of pages: 9
Pages: 1-9
Publication date: 2020
Peer-reviewed: Yes

Publication information

Journal: Biomedical Glasses
Volume: 6
Issue number: 1
ISSN (Print): 2299-3932
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Borosilicate glasses, Direct particle doping method, Dy microparticles, In-vitro testing, Persistent luminescence, Scaffold, SrAlO:Eu

Bibliographical note

INT=phys,"Del Cerro, Paloma Roldan"
INT=bmte,"Teittinen, Henriikka"

Source: Scopus
Source ID: 85085038962

Research output: Contribution to journalArticleScientificpeer-review

First principles prediction of the solar cell efficiency of chalcopyrite materials  AgMX2(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
Ratings: 
  • Scopus rating (2019): CiteScore 1.7 SJR 0.341 SNIP 0.706
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

Bursty magnetic friction between polycrystalline thin films with domain walls

Two magnets in relative motion interact through their dipolar fields, making individual magnetic moments dynamically adapt to the changes in the energy landscape and bringing about collective magnetization dynamics. Some of the energy of the system is irrevocably lost through various coupling mechanisms between the spin degrees of freedom and those of the underlying lattice, resulting in magnetic friction. In this work, we use micromagnetic simulations to study magnetic friction in a system of two thin ferromagnetic films containing quenched disorder mimicking a polycrystalline structure. We observe bursts of magnetic activity resulting from repeated domain wall pinning due to the disorder and subsequent depinning triggered by the dipolar interaction between the moving films. These domain wall jumps result in strong energy dissipation peaks. We study how the properties of the polycrystalline structure such as grain size and strength of the disorder, along with the driving velocity and the width of the films, affect the magnetization dynamics, average energy dissipation, and the statistical properties of the energy dissipation bursts.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Aalto University
Contributors: Rissanen, I., Laurson, L.
Number of pages: 9
Publication date: 4 Oct 2019
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 100
Issue number: 14
Article number: 144408
ISSN (Print): 2469-9950
Ratings: 
  • Scopus rating (2019): SJR 1.811 SNIP 1.025
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 85073384530

Research output: Contribution to journalArticleScientificpeer-review

Realization of Free-Space Long-Distance Self-Healing Bessel Beams

A new approach for generating long-distance self-healing Bessel beams, which is based on a ring-shaped (annular) lens and a spherical lens in 4f-configuration, is reported. With this, diffraction-free light evolution of a zeroth order Bessel beam over several meters is shown and available scaling opportunities that surpass current technologies by far are discussed. Furthermore, it is demonstrated how this setup can be adapted to create Bessel beam superpositions, realizing the longest ever reported optical conveyor beam and helicon beam, respectively. Last, the self-healing capabilities of the beams are tested against strong opaque and non-opaque scatterers, which again emphasizes the great potential of this new method.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Friedrich-Schiller-University Jena, UMR 6174, Fraunhofer Institute for Applied Optics and Precision Engineering IOF, Vacom GmbH, Institute of Applied Physics, Institut für Physik, Universität Rostock, Albert
Contributors: Vetter, C., Steinkopf, R., Bergner, K., Ornigotti, M., Nolte, S., Gross, H., Szameit, A.
Publication date: 1 Oct 2019
Peer-reviewed: Yes

Publication information

Journal: Laser and Photonics Reviews
Volume: 13
Issue number: 10
Article number: 1900103
ISSN (Print): 1863-8880
Ratings: 
  • Scopus rating (2019): SJR 4.014 SNIP 2.903
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Condensed Matter Physics
Keywords: beam-shaping, Bessel-beams, laser-technology, self-healing, telecommunication
Source: Scopus
Source ID: 85073597306

Research output: Contribution to journalArticleScientificpeer-review

Analytical computation of the demagnetizing energy of thin-film domain walls

Due to its nonlocal nature, calculating the demagnetizing field remains the biggest challenge in understanding domain structures in ferromagnetic materials. Analytical descriptions of demagnetizing effects typically approximate domain walls as uniformly magnetized ellipsoids, neglecting both the smooth rotation of magnetization from one domain to the other and the interaction between the two domains. Here, instead of the demagnetizing field, we compute analytically the demagnetizing energy of a straight domain wall described by the classical tanh magnetization profile in a thin film with perpendicular magnetic anisotropy. We then use our expression for the demagnetizing energy to derive an improved version of the 1D model of field-driven domain wall motion, resulting in accurate expressions for important properties of the domain wall such as the domain wall width and the Walker breakdown field. We verify the accuracy of our analytical results by micromagnetic simulations.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research area: Computational Physics
Contributors: Skaugen, A., Murray, P., Laurson, L.
Publication date: 25 Sep 2019
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 100
Issue number: 9
Article number: 094440
ISSN (Print): 2469-9950
Ratings: 
  • Scopus rating (2019): SJR 1.811 SNIP 1.025
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 85072773246

Research output: Contribution to journalArticleScientificpeer-review

Observation of PT-symmetric quantum interference

A common wisdom in quantum mechanics is that the Hamiltonian has to be Hermitian in order to ensure a real eigenvalue spectrum. Yet, parity–time (PT)-symmetric Hamiltonians are sufficient for real eigenvalues and therefore constitute a complex extension of quantum mechanics beyond the constraints of Hermiticity. However, as only single-particle or classical wave physics has been exploited so far, an experimental demonstration of the true quantum nature of PT symmetry has been elusive. In our work, we demonstrate two-particle quantum interference in a PT-symmetric system. We employ integrated photonic waveguides to reveal that the quantum dynamics of indistinguishable photons shows strongly counterintuitive features. To substantiate our experimental data, we analytically solve the quantum master equation using Lie algebra methods. The ideas and results presented here pave the way for non-local PT-symmetric quantum mechanics as a novel building block for future quantum devices.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Universität Rostock, Albert
Contributors: Klauck, F., Teuber, L., Ornigotti, M., Heinrich, M., Scheel, S., Szameit, A.
Publication date: 16 Sep 2019
Peer-reviewed: Yes

Publication information

Journal: Nature Photonics
ISSN (Print): 1749-4885
Ratings: 
  • Scopus rating (2019): CiteScore 58.3 SJR 13.614 SNIP 7.931
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85073826086

Research output: Contribution to journalArticleScientificpeer-review

Magnetic non-contact friction from domain wall dynamics actuated by oscillatory mechanical motion

Magnetic friction is a form of non-contact friction arising from the dissipation of energy in a magnet due to spin reorientation in a magnetic field. In this paper, we study magnetic friction in the context of micromagnetics, using our recent implementation of smooth spring-driven motion (Rissanen and Laurson 2018 Phys. Rev. E 97 053301) to simulate ring-down measurements in two setups where domain wall dynamics is induced by mechanical motion. These include a single thin film with a domain wall in an external field and a setup mimicking a magnetic cantilever tip and substrate, in which the two magnets interact through dipolar interactions. We investigate how various micromagnetic parameters influence the domain wall dynamics actuated by the oscillatory spring-driven mechanical motion and the resulting damping coefficient. Our simulations show that the magnitude of magnetic friction can be comparable to other forms of non-contact friction. For oscillation frequencies lower than those inducing excitations of the internal structure of the domain walls, the damping coefficient is found to be independent of frequency. Hence, our results obtained in the frequency range from 8-112 MHz are expected to be relevant also for typical experimental setups operating in the 100 kHz range.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research area: Computational Physics, Aalto University, COMP Centre of Excellence
Contributors: Rissanen, I., Laurson, L.
Publication date: 13 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: Journal of Physics D: Applied Physics
Volume: 52
Issue number: 44
Article number: 445002
ISSN (Print): 0022-3727
Ratings: 
  • Scopus rating (2019): CiteScore 5.3 SJR 0.899 SNIP 1.144
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Acoustics and Ultrasonics, Surfaces, Coatings and Films
Keywords: magnetic friction, micromagnetics, thin films
Source: Scopus
Source ID: 85072336407

Research output: Contribution to journalArticleScientificpeer-review

Exploration of Two Layer Nb3Sn 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
Ratings: 
  • Scopus rating (2019): SJR 0.419 SNIP 1.108
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
Ratings: 
  • Scopus rating (2019): CiteScore 13.8 SJR 3.662 SNIP 3.037
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

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
Ratings: 
  • Scopus rating (2019): SJR 0.419 SNIP 1.108
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

AlGaAs/AlGaInP VECSELs with Direct Emission at 740-770 nm

An optically-pumped vertical-external-cavity surface-emitting laser (OP-VECSEL) with 3.25-W output power emitting around 750 nm is demonstrated. The gain structure incorporates AlGaAs quantum wells (QWs) and barriers, and AlGaInP claddings. The emission wavelength could be tuned from 740 to 770 nm. The development addresses the need for high brightness lasers at a wavelength range that has proven difficult to reach. The demonstrated structure exhibits polarization-related peculiarities, which cause polarization switching under increased pump power due to mode competition. The presence of birefringence inside the active region is attributed to known long-range ordering within the AlGaInP claddings which causes distorted beam profiles. This influence on laser features has not been reported in VECSELs so far.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics
Contributors: Nechay, K., Kahle, H., Penttinen, J., Rajala, P., Tukiainen, A., Ranta, S., Guina, M.
Number of pages: 4
Pages: 1245-1248
Publication date: 1 Aug 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Photonics Technology Letters
Volume: 31
Issue number: 15
ISSN (Print): 1041-1135
Ratings: 
  • Scopus rating (2019): SJR 0.945 SNIP 1.212
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: AlGaAs, AlGaInP, quantum well lasers, semiconductor disk lasers, semiconductor growth, semiconductor laser, vertical-external-cavity surface-emitting lasers (VECSELs)

Bibliographical note

INT=phys,"Rajala, Patrik"

Source: Scopus
Source ID: 85069529749

Research output: Contribution to journalArticleScientificpeer-review

Temporal ghost imaging using wavelength conversion and two-color detection

Ghost imaging constructs an image by correlating two signals: one that interacts with an object but possesses no spatial information, and the other that contains spatial information but does not interact with the object. Ghost imaging can be extended into the time domain by using laser intensity fluctuations to reconstruct an unknown time-varying pattern, but this requires the measurement of laser fluctuations on ultrafast timescales, a significant limitation at wavelengths where ultrafast detectors are not available.We overcome this by using wavelength conversion to shift the probe laser into a spectral region where ultrafast detectors are available, and we apply this technique to image a temporal object at 2 μm. Our results demonstrate that temporal correlation information can be transferred to an arbitrary spectral region, opening possibilities for ultrafast ghost imaging at new wavelengths.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, University of Electronic Science and Technology of China, UMR 6174, Ita-Suomen yliopisto
Contributors: Wu, H., Ryczkowski, P., Friberg, A. T., Dudley, J. M., Genty, G.
Number of pages: 5
Pages: 902-906
Publication date: 20 Jul 2019
Peer-reviewed: Yes

Publication information

Journal: Optica
Volume: 6
Issue number: 7
ISSN (Print): 2334-2536
Ratings: 
  • Scopus rating (2019): CiteScore 18.1 SJR 5.6 SNIP 3.375
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics

Bibliographical note

INT=phys,"Wu, Han"

Source: Scopus
Source ID: 85071154886

Research output: Contribution to journalArticleScientificpeer-review

0.6V threshold voltage thin film transistors with solution processable indium oxide (In2O3) Channel and Anodized High-κ Al2O3 Dielectric

Low-voltage operation and low processing temperature of metal oxide transistors remain a challenge. Commonly metal oxide transistors are fabricated at very high processing temperatures (above 500°C) and their operating voltage is quite high (30-50 V). Here, thin-film transistors (TFT) are reported based upon solution processable indium oxide (In2O3) and room temperature processed anodized high- κ aluminum oxide (Al2O3) for gate dielectrics. The In2O3 TFTs operate well below the drain bias (Vds) of 3.0 V, with on/off ratio 105, subthreshold swing (SS) 160 mV/dec, hysteresis 0.19 V, and low threshold voltage (Vth)~0.6 V. The electron mobility (μ) is as high as 3.53 cm2/V.s in the saturation regime and normalized transconductance (gm) is 75μS/mm. In addition, the detailed capacitance-voltage (C-V) analysis to determine interface trap states density was also investigated. The interface trap density (Dit) in the oxide/semiconductor interface was quite low, i.e., 0.99 × 1011 - 2.98 × 1011 eV-1· cm2, signifying acceptable compatibility of In2O3 with anodic Al2O3.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Engineering, Columbia University in the City of New York, VTT Technical Research Centre of Finland, Department of Electrical and Computer Engineering, Ohio State University
Contributors: Bhalerao, S. R., Lupo, D., Zangiabadi, A., Kymissis, I., Leppäniemi, J., Alastalo, A., Berger, P. R.
Number of pages: 4
Pages: 1112-1115
Publication date: 1 Jul 2019
Peer-reviewed: Yes

Publication information

Journal: IEEE Electron Device Letters
Volume: 40
Issue number: 7
ISSN (Print): 0741-3106
Ratings: 
  • Scopus rating (2019): CiteScore 7.4 SJR 1.397 SNIP 1.633
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering
Keywords: anodization, indium oxide (InO), interface state density, low voltage, Metal oxide semiconductors, solution processing, TFT
Source: Scopus
Source ID: 85068181785

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
Ratings: 
  • Scopus rating (2019): SJR 1.827 SNIP 1.799
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

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
Ratings: 
  • Scopus rating (2019): SJR 0.419 SNIP 1.108
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

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
Ratings: 
  • Scopus rating (2019): SJR 1.811 SNIP 1.025
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

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
Ratings: 
  • Scopus rating (2019): CiteScore 4.4 SJR 0.594 SNIP 1.068
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

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
Ratings: 
  • Scopus rating (2019): SJR 1.811 SNIP 1.025
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

Fundamental gaps of quantum dots on the cheap

We show that the fundamental gaps of quantum dots can be accurately estimated at the computational effort of a standard ground-state calculation supplemented with a non-self-consistent step of negligible cost, all performed within density-functional theory at the level of the local-density approximation.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Quantum Control and Dynamics, Universita degli Studi di Modena e Reggio Emilia, Centro S3
Contributors: Guandalini, A., Rozzi, C. A., Räsänen, E., Pittalis, S.
Publication date: 25 Mar 2019
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 99
Issue number: 12
Article number: 125140
ISSN (Print): 2469-9950
Ratings: 
  • Scopus rating (2019): SJR 1.811 SNIP 1.025
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 85064152482

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
Ratings: 
  • Scopus rating (2019): CiteScore 13.8 SJR 3.662 SNIP 3.037
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
Ratings: 
  • Scopus rating (2019): CiteScore 6.1 SJR 0.891 SNIP 1.31
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

Experimental realization of wave-packet dynamics in cyclic quantum walks

Quantum walks present novel tools for redesigning quantum algorithms, universal quantum computations, and quantum simulators. Hitherto, one- and two-dimensional quantum systems (lattices) have been simulated and studied with photonic systems. Here, we report the photonic simulation of cyclic quantum systems, such as hexagonal structures. We experimentally explore the wavefunction dynamics and probability distribution of a quantum particle located on a six-site system, along with three- and four-site systems while under different initial conditions. Various quantum walk systems employing Hadamard, C-NOT, and Pauli-Z gates are experimentally simulated, where we find configurations capable of simulating particle transport and probability density localization. Our technique can potentially be integrated into small-scale structures using microfabrication, and thus would open a venue towards simulating more complicated quantum systems comprised of cyclic structures.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: University of Ottawa, Canada, Austrian Academy of Sciences
Contributors: Nejadsattari, F., Zhang, Y., Bouchard, F., Larocque, H., Sit, A., Cohen, E., Fickler, R., Karimi, E.
Number of pages: 7
Pages: 174-180
Publication date: 20 Feb 2019
Peer-reviewed: Yes

Publication information

Journal: Optica
Volume: 6
Issue number: 2
ISSN (Print): 2334-2536
Ratings: 
  • Scopus rating (2019): CiteScore 18.1 SJR 5.6 SNIP 3.375
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85063372591

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
Ratings: 
  • Scopus rating (2019): SJR 1.811 SNIP 1.025
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
Ratings: 
  • Scopus rating (2019): CiteScore 13.8 SJR 3.662 SNIP 3.037
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

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
Ratings: 
  • Scopus rating (2019): CiteScore 4.4 SJR 0.594 SNIP 1.068
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

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
Ratings: 
  • Scopus rating (2019): SJR 0.419 SNIP 1.108
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

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
Ratings: 
  • Scopus rating (2019): SJR 0.365 SNIP 0.661
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

Mechanical characterization of pore-graded bioactive glass scaffolds produced by robocasting

Since the discovery of 45S5 Bioglass® by Larry Hench, bioactive glasses have been widely studied as bone substitute materials and, in more recent years, have also shown great promise for producing three-dimensional scaffolds. The development of additive manufacturing techniques and their application in bone tissue engineering allows the design and fabrication of complex structures with controlled porosity. However, achieving strong and mechanically-reliable bioactive glass scaffolds is still a great challenge. Furthermore, there is a relative paucity of studies reporting an exhaustive assessment of other mechanical properties than compressive strength of glass-derived scaffolds. This research work aimed at determining key mechanical properties of silicate SiO2-Na2O-K2OMgO-CaO-P2O5 glass scaffolds fabricated by robocasting and exhibiting a porosity gradient. When tested in compression, these scaffolds had a strength of 6 MPa, a Young's modulus around 340 MPa, a fracture energy of 93 kJ/m3 and a Weibull modulus of 3, which provides a quantification of the scaffold reliability and reproducibility. Robocasting was a suitable manufacturing method to obtain structures with favorable porosity and mechanical properties comparable to those of the human cancellous bone, which is fundamental regarding osteointegration of bone implants.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Politecnico di Torino, McGill University
Contributors: Barberi, J., Nommeots-Nomm, A., Fiume, E., Verné, E., Massera, J., Baino, F.
Number of pages: 8
Pages: 140-147
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Biomedical Glasses
Volume: 5
Issue number: 1
ISSN (Print): 2299-3932
Ratings: 
  • Scopus rating (2019): CiteScore 2.9 SJR 0.39 SNIP 1.056
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Bioactive glass, Mechanical properties, Robocasting, Scaffold

Bibliographical note

EXT="Nommeots-Nomm, Amy"

Source: Scopus
Source ID: 85078096149

Research output: Contribution to journalArticleScientificpeer-review

How well can we predict cluster fragmentation inside a mass spectrometer?

Fragmentation of molecular clusters inside mass spectrometers is a significant source of uncertainty in a wide range of chemical applications. We have measured the fragmentation of sulfuric acid clusters driving atmospheric new-particle formation, and developed a novel model, based on first principles calculations, capable of quantitatively predicting the extent of fragmentation.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: University of Helsinki, Beijing University of Chemical Technology, CNRS, Centre National de la Recherche Scientifique (CNRS), Universite de Bordeaux - PRES, Lab Bordelais Rech Informat, PICTURA Res Grp, UMR 5800
Contributors: Passananti, M., Zapadinsky, E., Zanca, T., Kangasluoma, J., Myllys, N., Rissanen, M. P., Kurtén, T., Ehn, M., Attoui, M., Vehkamäki, H.
Number of pages: 4
Pages: 5946-5949
Publication date: 2019
Peer-reviewed: Yes

Publication information

Journal: Chemical Communications
Volume: 55
Issue number: 42
ISSN (Print): 1359-7345
Ratings: 
  • Scopus rating (2019): CiteScore 9.8 SJR 1.992 SNIP 1.144
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: 85065980333

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 16.4 SJR 4.224 SNIP 1.797
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

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 0.987
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

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 15.6 SJR 4.914 SNIP 3.162
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 4 SJR 0.744 SNIP 1.014
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

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 1.019
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

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 3.9 SJR 0.59 SNIP 1.025
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

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 2.42
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

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 4 SJR 0.744 SNIP 1.014
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 3.3 SJR 0.552 SNIP 1.269
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
Additional files: 
Source: Scopus
Source ID: 85049772255

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 4 SJR 0.744 SNIP 1.014
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 9 SJR 1.29 SNIP 1.342
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 2.7 SJR 0.463 SNIP 0.922
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

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 1.017
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
Electronic versions: 
URLs: 
Source: Scopus
Source ID: 85047240351

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 5.2 SJR 0.888 SNIP 1.297
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

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 0.987
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

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 5.2 SJR 0.888 SNIP 1.297
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 0.987
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

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 5.2 SJR 0.888 SNIP 1.297
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 0.987
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

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 0.958
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

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 4 SJR 0.744 SNIP 1.014
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

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 11.6 SJR 2.177 SNIP 1.145
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

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 0.987
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

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 5 SJR 0.886 SNIP 1.045
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

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 0.987
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

Stable blue phase polymeric Langmuir-Schaefer films based on unsymmetrical hydroxyalkadiynyl N-arylcarbamate derivatives

Unsymmetrical diynes containing N-arylcarbamate groups in the hydrophobic part and hydroxymethylene groups in the hydrophilic part of the molecules were synthesized and studied. The Langmuir monolayer formation process was followed by Brewster angle microscopy (BAM). The Langmuir-Schaefer monolayer films, transferred on solid substrates (quartz or Si), were investigated by absorption spectroscopy and atomic force microscopy (AFM). Four substances had 2 methylene groups in the hydrophilic part of the molecule (n) and 4 or 5 of these groups in the hydrophobic part (m). At the same time the aryl substituent had a hydrogen atom or a MeO group in the p-position of the benzene ring. After 20 min of UV irradiation the initially colorless monomeric films of all four compounds turned into stable blue phase polymeric films. The blue phase is unusual for alcoholic diacetylene derivatives. The BAM and AFM measurements demonstrated higher homogeneity of the films with a MeO group in the aryl substituent in comparison to the molecules with a hydrogen atom. The reasons for these different structural organizations as well as potential applications of stable blue phase polydiacetylene thin films are discussed.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Research group: Chemistry & Advanced Materials, A. M. Prokhorov General Physics Institute, Russian Academy of Sciences, Åbo Akademi University, St. Petersburg State University, Russian Academy of Science
Contributors: Alekseev, A., Ihalainen, P., Ivanov, A., Domnin, I., Rosqvist, E., Lemmetyinen, H., Vuorimaa-Laukkanen, E., Peltonen, J., Vyaz'min, S.
Number of pages: 11
Pages: 108-118
Publication date: 2018
Peer-reviewed: Yes
Early online date: 10 Oct 2017

Publication information

Journal: Thin Solid Films
Volume: 645
ISSN (Print): 0040-6090
Ratings: 
  • Scopus rating (2018): CiteScore 3.6 SJR 0.531 SNIP 0.837
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Surfaces and Interfaces, Surfaces, Coatings and Films, Metals and Alloys, Materials Chemistry
Keywords: Absorption spectroscopy, Blue phase polydiacetylenes, Brewster angle microscopy, Langmuir-Schaefer film, Photopolymerization

Bibliographical note

EXT="Alekseev, Alexander"

Source: Scopus
Source ID: 85032302551

Research output: Contribution to journalArticleScientificpeer-review

Essential Measurements for Finite Element Simulations of Magnetostrictive Materials

We discuss which magnetoelastic material properties are essential to measure in order to model magnetostrictive materials in finite element simulations. We show knowing the magnetic constitutive relation is sufficient, if the elastic behavior without magnetic field is known a priori. We neglect hysteresis, and our starting point is to express the effect of mechanical deformation on the magnetic constitutive relation with a small strain tensor and magnetic flux density. It follows that the (energetic) state of a magnetostrictive material is independent of its history. Then, a certain choice of history allows us to keep magnetism and elasticity distinct. We demonstrate with open source software Elmer, how one can set up such magnetoelastic simulations. These simulations rely on data obtained from magnetostrictive measurements. Finally, it is discussed how a measurement setup and the finite element model should be combined in order to verify the approach with experiments.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering
Contributors: Poutala, A., Kovanen, T., Kettunen, L.
Publication date: 2018
Peer-reviewed: Yes
Early online date: 16 Nov 2017

Publication information

Journal: IEEE Transactions on Magnetics
Volume: 54
Issue number: 1
Article number: 7200107
ISSN (Print): 0018-9464
Ratings: 
  • Scopus rating (2018): CiteScore 1.71 SJR 0.539 SNIP 1.019
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering
Keywords: Finite element analysis, Magnetic hysteresis, magnetomechanical coupling, Magnetostriction, magnetostriction, Strain, Tensile stress
Source: Scopus
Source ID: 85035114341

Research output: Contribution to journalArticleScientificpeer-review

Narrow-linewidth 780 nm DFB lasers fabricated using nanoimprint lithography

The paper presents narrow-linewidth 780 nm edgeemitting semiconductor DFB lasers fabricated without regrowth using UV-nanoimprinted surface gratings. The thirdorder laterally-coupled ridge-waveguide surface gratings enable single mode operation, excellent spectral purity (40-55 dB side mode suppression ratio and 10 kHz linewidth) and good lightcurrent- voltage characteristics in continuous wave operation (~112 mA threshold current, ~1.55 V opening voltage and 28.9 mW output power from one facet at 300 mA current for 2.4 mm long devices), which are vital in various applications, such as rubidium spectroscopy and atomic clock pumping. The low fabrication costs, high throughput, structural flexibility and high device yield make the fabrication method fully compatible with large scale mass production, enabling the fabrication of low-cost miniaturized modules.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics
Contributors: Virtanen, H., Uusitalo, T., Karjalainen, M., Ranta, S., Viheriala, J., Dumitrescu, M.
Pages: 51-54
Publication date: 2018
Peer-reviewed: Yes
Early online date: 9 Nov 2017

Publication information

Journal: IEEE Photonics Technology Letters
Volume: 30
Issue number: 1
ISSN (Print): 1041-1135
Ratings: 
  • Scopus rating (2018): CiteScore 2.89 SJR 0.991 SNIP 1.272
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: DFB laser, Gratings, Laser modes, Measurement by laser beam, narrow linewidth, Optical device fabrication, Optical interferometry, Surface emitting lasers, surface gratings, UV-nanoimprint lithography
Source: Scopus
Source ID: 85034223754

Research output: Contribution to journalArticleScientificpeer-review

Programming Photoresponse in Liquid Crystal Polymer Actuators with Laser Projector

A versatile, laser-projector-based method is demonstrated for programming alignment patterns into monolithic films of liquid crystal polymer networks. Complex images can be photopatterned into the polymer films with sub-100 μm resolution, using relatively short exposure times. The method is further used to devise both photochemically and photothermally driven actuators that can undergo distinct light-induced shape changes, dictated by the programmed alignment patterns. Deformation modes such as buckling and coiling, as well as miniature robotic devices such as a gripper and a light-responsive octopod, are demonstrated. The reported technique enables easy and cost-effective programmable actuation with relatively high throughput, thus significantly facilitating the design and realization of functional soft robotic actuators.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Research group: Chemistry & Advanced Materials, University of Warsaw
Contributors: Wani, O. M., Zeng, H., Wasylczyk, P., Priimagi, A.
Publication date: 2018
Peer-reviewed: Yes
Early online date: 2017

Publication information

Journal: Advanced Optical Materials
Volume: 6
Issue number: 1
Article number: 1700949
ISSN (Print): 2195-1071
Ratings: 
  • Scopus rating (2018): CiteScore 10.2 SJR 2.711 SNIP 1.6
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Keywords: Azobenzene, Laser projectors, Liquid crystal, Patterning, Photoactuation, Photoalignment
Electronic versions: 
Source: Scopus
Source ID: 85037631675

Research output: Contribution to journalArticleScientificpeer-review

Better understanding of the role of SiO2, P2O5 and Al2O3 on the spectroscopic properties of Yb3+ doped silica sol-gel glasses

Yb3+ doped silica sol-gel glass powders were prepared with different concentrations of SiO2, Al2O3 and P2O5 in order to understand the impact of the glass composition on the Yb3+ emission properties. In this paper, we clearly show that not only the Al/P ratio but also the SiO2 content have an impact on the Yb3+ spectroscopic properties. Our results provide new insight on the real impact of the composition on the spectroscopic properties of Yb3+ doped sol-gels: we demonstrate that an increase in the Al2O3 content at the expense of P2O5 leads to an increase in the intensity of the emission at 1000nm of the Yb3+ ions whereas an increase in the SiO2 content decreases it. We clearly showed that the inexpensive sol-gel approach can be easily used when investigating new Yb3+ doped silica glasses.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Nanophotonics, Faculty of Biomedical Sciences and Engineering, Research group: Biomaterials and Tissue Engineering Group, Research group: Photonics Glasses, Institut de Chimie de la Matiere Condensee de Bordeaux, Turun Yliopisto/Turun Biomateriaalikeskus
Contributors: Glorieux, B., Salminen, T., Massera, J., Lastusaari, M., Petit, L.
Pages: 46-51
Publication date: 2018
Peer-reviewed: Yes
Early online date: 2017

Publication information

Journal: Journal of Non-Crystalline Solids
Volume: 482
ISSN (Print): 0022-3093
Ratings: 
  • Scopus rating (2018): CiteScore 4.3 SJR 0.689 SNIP 1.186
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Condensed Matter Physics, Materials Chemistry
Keywords: Silica glass, Sol-gel, Spectroscopic properties, Yb doping
Source: Scopus
Source ID: 85037629421

Research output: Contribution to journalArticleScientificpeer-review

Light-trapping enhanced thin-film III-V quantum dot solar cells fabricated by epitaxial lift-off

We report thin-film InAs/GaAs quantum dot (QD) solar cells with n-i-p+ deep junction structure and planar back reflector fabricated by epitaxial lift-off (ELO) of full 3-in wafers. External quantum efficiency measurements demonstrate twofold enhancement of the QD photocurrent in the ELO QD cell compared to the wafer-based QD cell. In the GaAs wavelength range, the ELO QD cell perfectly preserves the current collection efficiency of the baseline single-junction ELO cell. We demonstrate by full-wave optical simulations that integrating a micro-patterned diffraction grating in the ELO cell rearside provides more than tenfold enhancement of the near-infrared light harvesting by QDs. Experimental results are thoroughly discussed with the help of physics-based simulations to single out the impact of QD dynamics and defects on the cell photovoltaic behavior. It is demonstrated that non radiative recombination in the QD stack is the bottleneck for the open circuit voltage (Voc) of the reported devices. More important, our theoretical calculations demonstrate that the Voc offset of 0.3. V from the QD ground state identified by Tanabe et al., 2012, from a collection of experimental data of high quality III-V QD solar cells is a reliable - albeit conservative - metric to gauge the attainable Voc and to quantify the scope for improvement by reducing non radiative recombination. Provided that material quality issues are solved, we demonstrate - by transport and rigorous electromagnetic simulations - that light-trapping enhanced thin-film cells with twenty InAs/GaAs QD layers reach efficiency higher than 28% under unconcentrated light, ambient temperature. If photon recycling can be fully exploited, 30% efficiency is deemed to be feasible.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC, Research group: Nanophotonics, Politecnico di Torino, Department of Applied Health Research, Radboud University Nijmegen, tf2 devices B.V.
Contributors: Cappelluti, F., Kim, D., van Eerden, M., Cédola, A. P., Aho, T., Bissels, G., Elsehrawy, F., Wu, J., Liu, H., Mulder, P., Bauhuis, G., Schermer, J., Niemi, T., Guina, M.
Pages: 83-92
Publication date: 2018
Peer-reviewed: Yes

Publication information

Journal: Solar Energy Materials and Solar Cells
Volume: 181
ISSN (Print): 0927-0248
Ratings: 
  • Scopus rating (2018): CiteScore 5.94 SJR 1.62 SNIP 1.681
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Renewable Energy, Sustainability and the Environment, Surfaces, Coatings and Films
Keywords: Epitaxial lift-off, Light-trapping, Quantum dot, Solar cell, Thin-film
Source: Scopus
Source ID: 85039853836

Research output: Contribution to journalArticleScientificpeer-review

Magnetic and mechanical design of a 16 T common coil dipole for FCC

EuroCirCol is a conceptual design study for a post-LHC research infrastructure based on an energy-frontier 100 TeV circular hadron collider. In the frame of the high-field accel-erator magnet design work package of this study, the feasibility of a 16-T dipole in common coil configuration is being studied. This paper shows the electromagnetic design optimization per-formed to achieve the required field quality while minimizing the superconductor volume and taking into account the input pa-rameters and assumptions of EuroCirCol study. Finite Element Models (FEM) have been used to analyze the stress distribution and deformations under the large Lorentz forces due to the very high magnetic field. Several iterations have been necessary to obtain a feasible magnet design. 3-D electromagnetic calculations are also included in this paper.

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, CIEMAT
Contributors: Toral, F., Munilla, J., Salmi, T.
Publication date: 2018
Peer-reviewed: Yes
Early online date: 24 Jan 2018

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 28
Issue number: 3
Article number: 4004305
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2018): CiteScore 1.65 SJR 0.406 SNIP 0.987
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: 16 Tesla, Accelerator magnets, FCC, high field magnets, superconducting magnets
Source: Scopus
Source ID: 85040982105

Research output: Contribution to journalArticleScientificpeer-review

Design of a Nb3Sn 400 T/m quadrupole for the Future Circular Collider

For the Future Circular Collider (FCC), a 100 TeV post Large Hadron Collider machine, 750 main quadrupoles with a gradient of around 400 T/m are required. This paper presents an electromagnetic design optimization of a double aperture Nb3Sn quadrupole, fulfilling the specifications and a structural design of a single aperture configuration towards a prototype

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, Institut de Recherche sur les Lois Fondamentales de l'Univers, Service des accelerateurs, de cryogenie et de magnetisme, European Organization for Nuclear Research
Contributors: Lorin, C., Simon, D., Felice, H., Rifflet, J. M., Salmi, T., Schoerling, D.
Publication date: 2018
Peer-reviewed: Yes
Early online date: 24 Jan 2018

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 28
Issue number: 3
Article number: 4004905
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2018): CiteScore 1.65 SJR 0.406 SNIP 0.987
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: 4 layers, FCC, main quadrupoles, Nb3Sn, superconducting quadrupole
Source: Scopus
Source ID: 85040993010

Research output: Contribution to journalArticleScientificpeer-review

Open Material Property Library With Native Simulation Tool Integrations - MASTO

Reliable material property data is crucial for trustworthy simulations throughout different areas of engineering.Special care must be taken when materials at extreme conditions are under study. Superconductors and devices assembled from superconductors and other materials, like superconducting magnets, are often operated at such extreme conditions: at low temperatures under high magnetic fields and stresses.Typically, some library or database is used for getting the data. We have started to develop a database for storing all kind of material property data online called Open Material Property Library With Native Simulation Tool Integrations -- MASTO. Data can also depend on other data and it can be versioned to guarantee permanent access. Guiding idea in MASTO is to build easy-to-use integration for various programming languages, modelling frameworks and simulation software. Currently, a full-fledged integration is built for Matlab to allow users to fetch and use data with one-liners.In this paper we briefly review some of the material property databases commonly used in superconductor modelling, present a case study showing how selection of the material property data can influence the simulation results, and introduce the principal ideas behind MASTO.This work serves as the reference document for citing MASTO when it is used in simulations.

General information

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

Publication information

Journal: IEEE Transactions on Applied Superconductivity
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2018): CiteScore 1.65 SJR 0.406 SNIP 0.987
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Data models, Databases, experimental data, Libraries, Material properties, material property database, NIST, numerical modelling, simulations, Superconducting magnets, Temperature
Source: Scopus
Source ID: 85041392089

Research output: Contribution to journalArticleScientificpeer-review

10 kA Joints for HTS Roebel Cables

Future HTS high field magnets using multi-tape HTS cables need 10 kA low resistance connections. The connections are needed between the poles of the magnets and at the terminals in a wide operating temperature range, from 1.9-85 K. The EuCARD WP10 Future Magnets collaboration aims at testing HTS based Roebel cables in an accelerator magnet. Usually, LTS cables are jointed inside a relatively short soldered block. Powering tests at CERN have highlighted excess heating of a joint following classical LTS joint design. The HTS Roebel cables are assembled from REBCO coated conductor tapes in a transposed configuration. Due to this, the tapes surface the cable at an angle with the cable axis. A low-resistance joint requires a sufficiently large interface area for each tape. Within one twist pitch length, each tape is located at the surface of the cable over a relatively small non-constant area. This geometry prevents making a well-controlled joint in a compact length along the cable. This paper presents a compact joint configuration for the Roebel cable overcoming these practical challenges. A new joint called fin-block is designed. The joint resistance is estimated computationally. Finally the test results as a function of current and temperature are presented.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, European Organization for Nuclear Research
Contributors: Murtomaeki, J. S., Kirby, G., van Nugteren, J., Contat, P. A., Fleiter, J., De Frutos, O. S., Pincot, F. O., DeRijk, G., Rossi, L., Ruuskanen, J., Stenvall, A., Wolf, F.
Publication date: 2018
Peer-reviewed: Yes
Early online date: 9 Feb 2018

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 0.987
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Cables and current leads, Heating systems, High-temperature superconductors, HTS Magnets, Pressure Measurement, Resistance, Resistance measurement, Soldering, Superconducting cables, Superconducting magnets, Superconducting Magnets, Temperature measurement
Source: Scopus
Source ID: 85041856536

Research output: Contribution to journalArticleScientificpeer-review

Sub-100 ps monolithic diamond Raman laser emitting at 573 nm

We report a compact and efficient picosecond diamond Raman laser at 573 nm wavelength. The laser consists of a 0.5 mm thick single-crystal synthetic diamond coated to form a plane&#x2013;plane laser resonator, and pumped at 532 nm by a frequency-doubled Q-switched microchip laser system. The pump delivers 85 ps pulses at 100 kHz repetition rate at a maximum average power of &#x007E;500 mW. We demonstrate 1st Stokes emission from the diamond Raman laser with maximum power of 175 mW, corresponding to a conversion efficiency of 47&#x0025; and a pulse duration of 71 ps. Substantial pulse shortening is obtained by proper adjustment of the pump spot diameter on the diamond sample. A minimum pulse duration of 39 ps is reported for a conversion efficiency of 36&#x0025; and 150 mW output power. The simplicity of the architecture makes the system highly appealing as a yellow picosecond laser source.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: ORC, University of Strathclyde
Contributors: Nikkinen, J., Savitski, V., Reilly, S., Dziechciarczyk, L., Härkönen, A., Kemp, A., Guina, M.
Pages: 981-984
Publication date: 2018
Peer-reviewed: Yes
Early online date: 13 Feb 2018

Publication information

Journal: IEEE Photonics Technology Letters
Volume: 30
Issue number: 11
ISSN (Print): 1041-1135
Ratings: 
  • Scopus rating (2018): CiteScore 2.89 SJR 0.991 SNIP 1.272
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: Diamond, Diamond Raman lasers, Laser excitation, Lenses, Microchip lasers, Power generation, Pulsed lasers, Pump lasers, Q-switched lasers, Raman lasers, Stimulated emission, Visible lasers
Source: Scopus
Source ID: 85042062344

Research output: Contribution to journalArticleScientificpeer-review

Real-time full-field characterization of transient dissipative soliton dynamics in a mode-locked laser

Dissipative solitons are remarkably localized states of a physical system that arise from the dynamical balance between nonlinearity, dispersion and environmental energy exchange. They are the most universal form of soliton that can exist, and are seen in far-from-equilibrium systems in many fields, including chemistry, biology and physics. There has been particular interest in studying their properties in mode-locked lasers, but experiments have been limited by the inability to track the dynamical soliton evolution in real time. Here, we use simultaneous dispersive Fourier transform and time-lens measurements to completely characterize the spectral and temporal evolution of ultrashort dissipative solitons as their dynamics pass through a transient unstable regime with complex break-up and collisions before stabilization. Further insight is obtained from reconstruction of the soliton amplitude and phase and calculation of the corresponding complex-valued eigenvalue spectrum. These findings show how real-time measurements provide new insights into ultrafast transient dynamics in optics.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, UMR 6174
Contributors: Ryczkowski, P., Närhi, M., Billet, C., Merolla, J. M., Genty, G., Dudley, J. M.
Number of pages: 7
Pages: 221–227
Publication date: 2018
Peer-reviewed: Yes
Early online date: 5 Mar 2018

Publication information

Journal: Nature Photonics
Volume: 12
ISSN (Print): 1749-4885
Ratings: 
  • Scopus rating (2018): CiteScore 59.9 SJR 13.456 SNIP 8.761
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 85042848951

Research output: Contribution to journalArticleScientificpeer-review

Efficient photon upconversion at remarkably low annihilator concentrations in a liquid polymer matrix: when less is more

A green-to-blue triplet-triplet annihilation upconversion of 24.5% quantum yield was achieved at a remarkably low 600 μM annihilator concentration in a viscous polymer matrix. This was made possible by utilizing a ZnTPP-based photosensitizer with exceptionally long 11 ms phosphorescence lifetime. Higher 3 mM annihilator concentration resulted in lower 24% upconversion quantum yield.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering
Contributors: Durandin, N. A., Isokuortti, J., Efimov, A., Vuorimaa-Laukkanen, E., Tkachenko, N. V., Laaksonen, T.
Number of pages: 4
Pages: 14029-14032
Publication date: 2018
Peer-reviewed: Yes

Publication information

Journal: Chemical Communications
Volume: 54
Issue number: 99
ISSN (Print): 1359-7345
Ratings: 
  • Scopus rating (2018): CiteScore 11.6 SJR 2.177 SNIP 1.145
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
Keywords: triplet-triplet annihilation, triplet-triplet energy transfer, triplet state lifetime, upconversion, triplet fusion
URLs: 
Source: Scopus
Source ID: 85058301188

Research output: Contribution to journalArticleScientificpeer-review

Electro-optic steering of random laser emission in liquid crystals

Using an external low-frequency electric field applied to dye-doped nematic liquid crystals, we demonstrate that random lasing obtained by optical pumping can be steered in an angular direction by routing an all-optical waveguide able to collect the emitted light. By varying the applied voltage from 0 to 2 V, we reduce the walk-off and sweep the random laser guided beam over 7 degrees.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Nonlinear Optics, University of Rome Roma Tre, University “Roma Tre”
Contributors: Assanto, G., Perumbilavil, S., Piccardi, A., Kauranen, M.
Number of pages: 3
Pages: 103-105
Publication date: 2018
Peer-reviewed: Yes

Publication information

Journal: Photonics Letters of Poland
Volume: 10
Issue number: 4
ISSN (Print): 2080-2242
Ratings: 
  • Scopus rating (2018): CiteScore 0.8 SJR 0.214 SNIP 0.357
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials
Source: Scopus
Source ID: 85062032353

Research output: Contribution to journalArticleScientificpeer-review

Crystallization of supercooled liquid antimony: A density functional study

Crystallization of liquid antimony has been studied at 600 K using six density functional/molecular dynamics simulations with up to 882 atoms and three scenarios: one completely disordered sample that did not crystallize even after 570 ps, four with fixed crystalline slab templates, and one with a fixed crystalline seed. Crystallization proceeded layer-by-layer in most cases and was rapid (∼36 m/s) with templates and somewhat slower with the seed. The seed simulation shows an unusual percolation asymmetry where the crystallite grows faster in the direction normal to the zigzag planes. Changes in pair distribution functions, bond angle distributions, ring statistics, nearest-neighbor distances, and cavity volumes were monitored. Diffusion plays a minor role in the process, and the evolution of bond lengths and ring statistics supports the bond-interchange model introduced to explain the rapid crystallization of Sb-rich phase change materials.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Aalto University, Norwegian Univ. of Sci. and Technol., Forschungszentrum Jülich (FZJ)
Contributors: Ropo, M., Akola, J., Jones, R. O.
Publication date: 3 Nov 2017
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 96
Issue number: 18
Article number: 184102
ISSN (Print): 2469-9950
Ratings: 
  • Scopus rating (2017): CiteScore 3.34 SJR 1.604 SNIP 1.149
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 85038856403

Research output: Contribution to journalArticleScientificpeer-review

Investigating solvent effects on aggregation behaviour, linear and nonlinear optical properties of silver nanoclusters

We herein report the solvent effects on the aggregation, linear and nonlinear optical properties of silver nanoclusters synthesised using three solvents namely; ethanol, acetone and isopropanol. The Ag clusters were characterized using UV–Visible (UV–vis) and photoluminescence (PL) spectroscopy, Fourier transform-infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), small angle X-ray scattering (SAXS), dynamic light scattering (DLS), and open aperture Z-Scan measurements. Density functional theory (DFT) calculations at the B3PW91 level of theory, were done to compute the electric dipole, quadrupole, octapole and hexadecapole moment of mercaptosuccinic acid and mercaptosuccinic acid-Ag9 cluster in three solvents. Linear optical properties show characteristic absorption profile with quantum confinement at different wavelengths for all the three clusters. The Open aperture Z-scan measurement in Ag clusters establishes the optical limiting properties which arise mostly from excited state absorption (ESA) and relatively weak saturable absorption (SA). The nonlinear optical behaviour varies within the three clusters with maximum optical limiting value obtained for the clusters synthesised using acetone. The theoretically computed hyperpolarizabilities together with z-scan measurements establish the solvent effect on the clusters and their potential applications in optical limiting devices.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, St Teresas’s College, Mahatma Gandhi University, Kolkata Centre, Birla Institute of Technology & Science, Swinburne University of Technology, University of Johannesburg
Contributors: Bhavitha, K. B., Nair, A. K., Perumbilavil, S., Joseph, S., Kala, M. S., Saha, A., Narayanan, R. A., Hameed, N., Thomas, S., Oluwafemi, O. S., Kalarikkal, N.
Number of pages: 11
Pages: 695-705
Publication date: 1 Nov 2017
Peer-reviewed: Yes

Publication information

Journal: Optical Materials
Volume: 73
ISSN (Print): 0925-3467
Ratings: 
  • Scopus rating (2017): CiteScore 3.7 SJR 0.592 SNIP 1.054
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: Aggregation behaviour, DFT, Linear optical properties, Non linear optical properties, Silver nanoclusters, Solvent effects
Source: Scopus
Source ID: 85030173026

Research output: Contribution to journalArticleScientificpeer-review

Paraxial light beams in structured anisotropic media

We discuss the paraxial approximation for optical waves propagating in a uniaxial anisotropic medium inhomogeneously twisted on the plane normal to the wave vector, with the latter being parallel to one of the two principal axes normal to the optic axis. Such geometry implies a continuous power transfer between the ordinary and extraordinary components, regardless of the input beam polarization. We pinpoint that this peculiar feature, generalizable to any inhomogeneous linear birefringent material, strongly affects the application of the paraxial approximation due to the simultaneous presence of two different phase velocities. We eventually show that a local coordinate transformation permits a correct application of the paraxial approximation.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Nonlinear Optics, Univ Porto, Universidade do Porto, Fac Med, Dept Med Imaging
Contributors: Jisha, C. P., Alberucci, A.
Number of pages: 6
Pages: 2019-2024
Publication date: 1 Nov 2017
Peer-reviewed: Yes

Publication information

Journal: Journal of the Optical Society of America A: Optics and Image Science, and Vision
Volume: 34
Issue number: 11
ISSN (Print): 1084-7529
Ratings: 
  • Scopus rating (2017): CiteScore 1.76 SJR 0.687 SNIP 1.098
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Computer Vision and Pattern Recognition
Source: Scopus
Source ID: 85033368214

Research output: Contribution to journalArticleScientificpeer-review

Generation of Sub-100 ps Pulses at 532, 355, and 266 nm Using a SESAM Q-Switched Microchip Laser

We report a single-frequency semiconductor saturable absorber mirror Q-switched microchip laser system generating sub-100 ps pulses at 532, 355, and 266 nm. The system consists of a 1064 nm Nd:YVO4 master oscillator, Nd:YVO4 power amplifier, and one or two nonlinear crystals for single-pass frequency-conversion to visible and UV. The average output power is about 720 mW at 532 nm, 150 mW at 355 nm and 83 mW at 266 nm for a pulse repetition rate of 100 kHz. At 532 nm the peak power is nearly 80 kW with pulse energy of about 7.2 μJ and spectral width of about 0.026 nm. The optical-to-optical conversion efficiency from 808 to 532 nm is about 8.3%. In comparison with mode-locked picosecond systems, the proposed laser has intrinsically low repetition rate, which is desirable in certain applications. The laser has also inherently narrow spectral width, and high peak power and pulse energy. This unique combination of output parameters could make the system useful in several applications including fluorescence lifetime imaging microscopy, high-accuracy submarine LIDAR, STED microscopy, time-gated Raman spectroscopy two-photon polymerization, diamond Raman laser pumping, photo-acoustic imaging, and micro-machining/marking.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics
Contributors: Nikkinen, J., Härkönen, A., Leino, I., Guina, M.
Number of pages: 4
Pages: 1816-1819
Publication date: 1 Nov 2017
Peer-reviewed: Yes

Publication information

Journal: IEEE Photonics Technology Letters
Volume: 29
Issue number: 21
ISSN (Print): 1041-1135
Ratings: 
  • Scopus rating (2017): CiteScore 2.84 SJR 0.961 SNIP 1.267
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: Microchip lasers, pulsed lasers, Q-switched lasers, UV lasers, visible lasers
Source: Scopus
Source ID: 85030256814

Research output: Contribution to journalArticleScientificpeer-review

Fluorimetric oxygen sensor with an efficient optical read-out for in vitro cell models

This paper presents a phase fluorimetric sensor for the monitoring of the oxygen concentration in in vitro cell models. The sensing surface of the sensor consists of oxygen sensitive fluorescent dyes (platinum(II) octaethylporphyrinketone) embedded in a thin polystyrene film. In order to optimize the optical read-out scheme of the sensor, we carried out electromagnetic simulations of a fluorescently doped polystyrene film deposited on a glass-water interface. The simulation results showed highly anisotropic angular emission distribution with the maximum irradiance being at super critical angles, which attracts tailored optical designs to maximize the fluorescence collection efficiency. For this purpose, we applied an efficient optical read-out scheme based on an in-contact parabolic lens. The use of parabolic lens also facilitates confocal total internal reflection excitation from the substrate side. This makes the excitation effective and insensitive to biofouling or other optical changes in the sensing surface and, more importantly, greatly reduces the amount of excitation power radiated into the cell culture chamber. Experimental results show that when applied together with phase fluorimetric lifetime sensing, this optical scheme allows one to use thin films (

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: BioMediTech, Faculty of Biomedical Sciences and Engineering, Research group: Micro and Nanosystems Research Group, Research area: Microsystems, Research group: Sensor Technology and Biomeasurements (STB), VTT Technical Research Centre of Finland, BioMediTech Institute and Faculty of Biomedical Sciences and Engineering
Contributors: Välimäki, H., Verho, J., Kreutzer, J., Kattipparambil Rajan, D., Ryynänen, T., Pekkanen-Mattila, M., Ahola, A., Tappura, K., Kallio, P., Lekkala, J.
Number of pages: 9
Pages: 738-746
Publication date: 1 Oct 2017
Peer-reviewed: Yes

Publication information

Journal: Sensors and Actuators B: Chemical
Volume: 249
ISSN (Print): 0925-4005
Ratings: 
  • Scopus rating (2017): CiteScore 9.3 SJR 1.406 SNIP 1.453
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Instrumentation, Condensed Matter Physics, Surfaces, Coatings and Films, Metals and Alloys, Materials Chemistry, Electrical and Electronic Engineering
Keywords: Cardiac cells, Enhanced optical read-out, Fluorimetric oxygen sensor, in vitro cell models, PtOEPK, Thin film fluorescence
Source: Scopus
Source ID: 85019164799

Research output: Contribution to journalArticleScientificpeer-review

Investigation of long-term chemical stability of structured ZnO films in aqueous solutions of varying conditions

Nanostructured zinc oxide, ZnO, films feature attractive functional properties, but their long-term stability needs further investigation. Here, ZnO thin films with well-aligned rod-like structure were grown on stainless steel substrate. The long-term chemical stability of the ZnO films was investigated in solutions with varying pH values (3 − 11) to enhance knowledge about the durability of films in acidic and basic environments. The solubility and stability of the films in the solutions were investigated using atomic absorption spectrophotometry, scanning electron microscopy imaging and energy-dispersive X-ray spectroscopy analyses, as well as by monitoring changes in water contact angle of the films and in the pH values of the solutions. The ZnO film was found to be most stable at highest pH value, with the amount of dissolved zinc being lowest among the studied pH values and the changes observed with other characterization methods being minor compared to the samples immersed to other solutions. At the lowest pH, the film was removed rapidly from the substrate by dissolution. In solutions featuring pH values 5 and 9, the measured pH was unstable and changed constantly until it reached the value 7.2–7.6, i.e., until the equilibrium of different chemical species in the solution was achieved. These results are presented and discussed in this paper from the viewpoint of applicability of the ZnO films.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Ceramic materials, VTT Technical Research Centre of Finland
Contributors: Heinonen, S., Nikkanen, J., Huttunen-Saarivirta, E., Levänen, E.
Number of pages: 10
Pages: 410-419
Publication date: 30 Sep 2017
Peer-reviewed: Yes

Publication information

Journal: Thin Solid Films
Volume: 638
ISSN (Print): 0040-6090
Ratings: 
  • Scopus rating (2017): CiteScore 3.8 SJR 0.617 SNIP 0.864
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Surfaces and Interfaces, Surfaces, Coatings and Films, Metals and Alloys, Materials Chemistry
Keywords: Chemical stability, Hydrothermal synthesis, pH, Solubility, Thin film, Zinc oxide
Source: Scopus
Source ID: 85027885831

Research output: Contribution to journalArticleScientificpeer-review

Statistical analysis of E-jet print parameter effects on Ag-nanoparticle ink droplet size

In this paper, we have studied the print parameter effects on electrohydrodynamic inkjet (E-jet) resolution using statistical analysis. In order to make the E-jet manufacturing process feasible, the effect of printing parameters on the ejected droplet size must be modelled and optimized. To this end, there exist two approaches: parameter effects can be modelled using theoretical calculations or they can be generated directly from empirical data using statistical analysis. The first option has been explored by multiple research groups, whereas the latter has received less interest. In this article, the effect of printing parameters on the width of AC-pulsed E-jet deposited Ag-nanoparticle ink droplets are investigated using design of experiments (DoE) approach and statistical analysis. As a result, a statistical model for deposited droplet width is generated using four print parameters (print height, bias voltage, peak voltage and frequency) as predictors. The model can predict 94.24% of the measured width variation with a standard deviation of 1.05 μm.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electronics and Communications Engineering, Research group: Laboratory for Future Electronics, Research group: Wireless Communications and Positioning
Contributors: Laurila, M. M., Khorramdel, B., Dastpak, A., Mäntysalo, M.
Publication date: 2 Aug 2017
Peer-reviewed: Yes

Publication information

Journal: Journal of Micromechanics and Microengineering
Volume: 27
Issue number: 9
Article number: 095005
ISSN (Print): 0960-1317
Ratings: 
  • Scopus rating (2017): CiteScore 3.7 SJR 0.554 SNIP 1.015
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Mechanics of Materials, Mechanical Engineering, Electrical and Electronic Engineering
Keywords: design of experiments, E-jet, printed electronics, statistical analysis
URLs: 

Bibliographical note

INT=elt,"Dastpak, A."

Source: Scopus
Source ID: 85028383527

Research output: Contribution to journalArticleScientificpeer-review

Computational super-resolution phase retrieval from multiple phase-coded diffraction patterns: Simulation study and experiments

In this paper, we consider computational super-resolution inverse diffraction phase retrieval. The optical setup is lensless, with a spatial light modulator for aperture phase coding. The paper is focused on experimental tests of the super-resolution sparse phase amplitude retrieval algorithm. We start from simulations and proceed to physical experiments. Both simulation tests and experiments demonstrate good-quality imaging for super-resolution with a factor of 4 and a serious advantage over diffraction-limited resolution as defined by Abbe’s criterion.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing, Research group: Computational Imaging-CI, Department of Photonics and Optical Information Technology, ITMO University
Contributors: Katkovnik, V., Shevkunov, I., Petrov, N. V., Egiazarian, K.
Number of pages: 9
Pages: 786-794
Publication date: 20 Jul 2017
Peer-reviewed: Yes

Publication information

Journal: Optica
Volume: 4
Issue number: 7
ISSN (Print): 2334-2536
Ratings: 
  • Scopus rating (2017): CiteScore 11.9 SJR 4.602 SNIP 2.811
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Keywords: Discrete optical signal processing, Image processing, Noise in imaging systems, Phase retrieval, Superresolution
Source: Scopus
Source ID: 85025162894

Research output: Contribution to journalArticleScientificpeer-review

Hafnium oxide thin films as a barrier against copper diffusion in solar absorbers

The thermal stability of copper substrate material used in solar thermal collectors was investigated with and without atomic layer deposited (ALD) hafnium oxide barrier films at temperatures of 200–400 °C. HfO2 films were studied as barriers against thermal diffusion of copper substrate atoms. The ALD HfO2 thin films were deposited in a thermal process at 200 °C using Tetrakis(Dimethylamido)Hafnium(Hf(NMe2)4) and H2O precursors, with 200, 400, and 600 cycles. The Cu substrates with and without HfO2 thin films were aged by means of heat treatment in air. The influence of the HfO2 barriers was determined by optical, microstructural, and morphological analyses before and after the ageing procedures. The optical performance of the HfO2 barriers as a part of solar absorber stack was modelled with CODE Coating Designer. The copper surface without a HfO2 barrier thin film oxidized significantly, which increased thermal emittance and surface roughness. 200 cycles of HfO2 deposition did not result in a completely continuous coating and only provided a little protection against oxidation. Films of 200 and 400 cycles gave continuous coverage and the thickest HfO2 thin film studied, which was deposited from 600 ALD cycles and had a thickness ~50 nm, prevented Cu oxidation and diffusion processes after 2 h heat treatment in air at 300 °C, and retained low thermal emissivity. At 400 °C, diffusion and formation of copper oxide hillocks were observed but the HfO2 thin film significantly retarded the degradation when compared to a Cu substrate without and with thinner barrier layers.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Research group: Surface Engineering, R&D Center for Low-Cost Plasma and Nanotechnology Surface Modifications (CEPLANT), Masaryk University
Contributors: Kotilainen, M., Krumpolec, R., Franta, D., Souček, P., Homola, T., Cameron, D. C., Vuoristo, P.
Number of pages: 7
Pages: 140-146
Publication date: 1 Jul 2017
Peer-reviewed: Yes

Publication information

Journal: Solar Energy Materials and Solar Cells
Volume: 166
ISSN (Print): 0927-0248
Ratings: 
  • Scopus rating (2017): CiteScore 4.83 SJR 1.459 SNIP 1.537
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Renewable Energy, Sustainability and the Environment, Surfaces, Coatings and Films
Keywords: Copper diffusion, Diffusion barrier, HfO thin film, Solar absorber, Thermal ageing
Source: Scopus
Source ID: 85016025672

Research output: Contribution to journalArticleScientificpeer-review

Long-Range Observation of Exciplex Formation and Decay Mediated by One-Dimensional Bridges

We report herein unprecedented long-range observation of both formation and decay of the exciplex state in donor (D)-bridge (B)-acceptor (A) linked systems. Zinc porphyrins (ZnP) as a donor were tethered to single-walled carbon nanotube (SWNT) as an acceptor through oligo(p-phenylene)s (ZnP-phn-SWNT) or oligo(p-xylene)s (ZnP-xyn-1-ph1-SWNT) with systematically varied lengths (n = 1-5) to address the issue. Exponential dependencies of rate constants for the exciplex formation (kFEX) and decay (kDEX) on the edge-to-edge separation distance between ZnP and SWNT through the bridges were unambiguously derived from time-resolved spectroscopies. Distance dependencies (i.e., attenuation factor, β) of kFEX and kDEX in ZnP-phn-SWNT were found to be considerably small (β = 0.10 for kFEX and 0.12 Å-1 for kDEX) compared to those for charge separation and recombination (0.2-0.8 Å-1) in D-B-A systems with the same oligo(p-phenylene) bridges. The small β values may be associated with the exciplex state with mixed characters of charge-transfer and excited states. In parallel, the substantially nonconjugated bridge of oligo(p-xylene)s exhibited larger attenuation values (β = 0.12 for kFEX and 0.14 Å-1 for kDEX). These results provide deep insight into the unique photodynamics of electronically strongly coupled D-B-A systems involving exciplex.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Research group: Chemistry & Advanced Materials, Kyoto Women's University
Contributors: Baek, J., Umeyama, T., Stranius, K., Yamada, H., Tkachenko, N. V., Imahori, H.
Number of pages: 10
Pages: 13952-13961
Publication date: 29 Jun 2017
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry C
Volume: 121
Issue number: 25
ISSN (Print): 1932-7447
Ratings: 
  • Scopus rating (2017): CiteScore 7.9 SJR 2.135 SNIP 1.133
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Energy(all), Surfaces, Coatings and Films, Physical and Theoretical Chemistry
Source: Scopus
Source ID: 85022231305

Research output: Contribution to journalArticleScientificpeer-review

Suitability of Different Quench Protection Methods for a 16 T Block-Type Nb3Sn Accelerator Dipole Magnet

Within the future circular collider study, a 100-km long circular hadron collider is being designed for 100 TeV center-of-mass collision energies. The design of the 16 T Nb3Sn bending dipole magnets is carried out within the EuroCirCol collaboration. Three different type of dipole designs have been developed, each aiming to be as compact as possible, accounting for the design criteria. Quench protection a critical aspect of the magnet design and potentially limits the magnet compactness. The EuroCirCol magnets were designed assuming a protection system with significantly improved efficiency compared to the present LHC dipole protection. In this paper, we consider present state-of-the-art quench protection technologies, such as quench heaters and CLIQ, and apply them into the designed 16 T Block-type dipole. Two different simulation models are used to estimate the magnet hotspot temperature and voltages after a quench and consequently estimate the suitability of the different methods.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, Research area: Electromagnetics, European Organization for Nuclear Research, Istituto Nazionale Di Fisica Nucleare, Frascati
Contributors: Salmi, T., Prioli, M., Stenvall, A., Ruuskanen, J., Verweij, A. P., Auchmann, B., Marinozzi, V.
Publication date: 1 Jun 2017
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 27
Issue number: 4
Article number: 4702305
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2017): CiteScore 1.45 SJR 0.408 SNIP 0.962
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: CLIQ, hotspot temperature, quench protection heaters, quench simulation, Superconducting magnets
Electronic versions: 
Source: Scopus
Source ID: 85015258090

Research output: Contribution to journalArticleScientificpeer-review

Dynamic speckle analysis with smoothed intensity-based activity maps

Pointwise intensity-based algorithms are the most popular algorithms in dynamic laser speckle measurement of physical or biological activity. The output of this measurement is a two-dimensional map which qualitatively separates regions of higher or lower activity. In the paper, we have proposed filtering of activity maps to enhance visualization and to enable quantitative determination of activity time scales. As a first step, we have proved that the severe spatial fluctuations within the map resemble a signal-dependent noise. As a second step, we have illustrated implementation of the proposed idea by applying filters to non-normalized and normalized activity estimates derived from synthetic and experimental data. Statistical behavior of the estimates has been analyzed to choose the filter parameters, and substantial narrowing of the probability density functions of the estimates has been achieved after the filtering. The filtered maps exhibit an improved contrast and allowed for quantitative description of activity.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing, Research group: 3D MEDIA, Bulgarian Academy of Sciences, Korea Electronics Technology Institute
Contributors: Stoykova, E., Berberova, N., Kim, Y., Nazarova, D., Ivanov, B., Gotchev, A., Hong, J., Kang, H.
Number of pages: 11
Pages: 55-65
Publication date: 1 Jun 2017
Peer-reviewed: Yes

Publication information

Journal: Optics and Lasers in Engineering
Volume: 93
ISSN (Print): 0143-8166
Ratings: 
  • Scopus rating (2017): CiteScore 6.2 SJR 1.018 SNIP 1.919
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Mechanical Engineering, Electrical and Electronic Engineering
Keywords: Digital image processing, Dynamic speckle, Speckle, Speckle metrology
Source: Scopus
Source ID: 85010222438

Research output: Contribution to journalArticleScientificpeer-review

Mechanical Effects of the Nonuniform Current Distribution on HTS Coils for Accelerators Wound With REBCO Roebel Cable

Future high-energy accelerators will need very high magnetic fields in the range of 20 T. The EuCARD-2 WP10 Future Magnets collaboration is aiming at testing HTS-based Roebel cables in an accelerator magnet. The demonstrator should produce around 17 T, when inserted into the 100-mm aperture of Feather-M2 13-T outsert magnet. HTS Roebel cables are assembled from meander-shaped REBCO-coated conductor tapes. In comparison with fair level of uniformity of current distribution in cables made out of round Nb-Ti or Nb3 Sn strands, current distribution within the coils wound from Roebel cables is highly nonhomogeneous. It results in nonuniform electromagnetic force distribution over the cable that could damage the very thin REBCO superconducting layer. This paper focuses on the numerical models to describe the effect of the nonhomogeneous current distribution on stress distribution in the demonstrator magnet designed for the EuCARD-2 project. Preliminary results indicate that the impregnation bonding between the cable glass fiber insulation and layer-to-layer insulation plays a significant role in the pressure distribution at the cable edges. The stress levels are safe for Roebel cables. Assuming fully bonded connection at the interface, the stresses around the edges are reduced by a large factor.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, Research group: Modelling and superconductivity, European Organization for Nuclear Research, University of Twente
Contributors: Murtomaki, J. S., Van Nugteren, J., Kirby, G., Rossi, L., Ruuskanen, J., Stenvall, A.
Publication date: 1 Jun 2017
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 27
Issue number: 4
Article number: 4100405
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2017): CiteScore 1.45 SJR 0.408 SNIP 0.962
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Accelerator dipoles, HTS magnets, Mechanical engineering, Superconducting magnets
Source: Scopus
Source ID: 85017606692

Research output: Contribution to journalArticleScientificpeer-review

First Cold Powering Test of REBCO Roebel Wound Coil for the EuCARD2 Future Magnet Development Project

EuCARD-2 is a project partly supported by FP7-European Commission aiming at exploring accelerator magnet technology for 20 T dipole operating field. The EuCARD-2 collaboration is liaising with similar programs for high field magnets in the USA and Japan. EuCARD-2 focuses, through the work-package 10 'Future magnets,' on the development of a 10 kA-class superconducting, high current density cable suitable for accelerator magnets, for a 5 T stand-alone dipole of 40 mm bore and about 1 m length. After standalone testing, the magnet will possibly be inserted in a large bore background dipole, to be tested at a peak field up to 18 T. This paper starts by reporting on a few of the highlight simulations that demonstrate the progress made in predicting: dynamic current distribution and influence on field quality, complex quench propagation between tapes, and minimum quench energy in the multitape cable. The multiphysics output importantly helps predicting quench signals and guides the development of the novel early detection systems. Knowing current position within individual tapes of each cable we present stress distribution throughout the coils. We report on the development of the mechanical component and assembly processes selected for Feather-M2 the 5 T EuCARD2 magnet. We describe the CERN variable temperature flowing helium cold gas test system. We describe the parallel integration of the FPGA early quench detection system, using pickup coils and temperature sensors, alongside the standard CERN magnet quench detection system using voltage taps. Finally we report on the first cold tests of the REBCO 10 kA class Roebel subscale coil named Feather-M0.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, Research group: Modelling and superconductivity, European Organization for Nuclear Research, IRFM, Karlsruhe Institute of Technology, Campus North, Bruker HTS
Contributors: Kirby, G. A., Van Nugteren, J., Bajas, H., Benda, V., Ballarino, A., Bajko, M., Bottura, L., Broekens, K., Canale, M., Chiuchiolo, A., Gentini, L., Peray, N., Perez, J. C., De Rijk, G., Rijllart, A., Rossi, L., Murtomaeki, J., Mazet, J., Pincot, F. O., Volpini, G., Durante, M., Fazilleau, P., Lorin, C., Stenvall, A., Goldacker, W., Kario, A., Usoskin, A.
Publication date: 1 Jun 2017
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 27
Issue number: 4
Article number: 4003307
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2017): CiteScore 1.45 SJR 0.408 SNIP 0.962
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: accelerators magnets, cryogenic systems, EuCARD-2, future magnets, high-temperature-superconductors, HTS, metal 3-D printing, Roebel cable, Superconducting magnets
Source: Scopus
Source ID: 85017652750

Research output: Contribution to journalArticleScientificpeer-review

Capability assessment of inkjet printing for reliable RFID applications

In this paper, inkjet-printed silver traces and interconnections produced with the print-on-slope technique were used in an radio-frequency identification (RFID) structure operating in the ultra-high-frequency range. Underfill material was used to attach silicon RFID chips onto flexible, 125-Êm-thick polymer substrates. The cured underfill was also used as a sloped surface for printing interconnection traces from the chip to the plastic substrates radiators. Inkjet printing was performed in one phase, producing both the interconnections to the chip and the radiators. This enables the use of a single-phase continuous roll-to-roll compatible process instead of the commonly used twophase stop-and-go process. To further investigate the behavior of the printed low-temperature nanoparticle ink and its compatibility with different substrate materials, basic conductive traces were printed onto the substrates. Thereafter, the structures were exposed to thermal/humidity tests at 85 ° C temperature/85% relative humidity (85/85%h) for up to a 2000-h period. To gain an understanding of the response of the structures under stress, the samples were intermittently characterized by using a read range measurement device, followed by the removal of failed samples from the test. The samples were characterized also by optical imaging and field-emission scanning electron microscopy. The bulk conductive traces were characterized electrically by measuring their resistances during test breaks. The results point out that although some challenges are still to overcome, inkjet printing is a feasible way of producing conductive traces for RFID structures, and that the print-on-slope technique is utilizable also in practical applications as a cost-effective method with adequate reliability for producing interconnections between chip and substrate.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electronics and Communications Engineering, Research group: Laboratory for Future Electronics, Univ of Oulu, Meyer Burger B.V., Microelectronics Research, School of Management (JKK)
Contributors: Putaala, J., Niittynen, J., Hannu, J., Myllymäki, S., Kunnari, E., Mäntysalo, M., Hagberg, J., Jantunen, H.
Number of pages: 10
Pages: 281-290
Publication date: 1 Jun 2017
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Device and Materials Reliability
Volume: 17
Issue number: 2
ISSN (Print): 1530-4388
Ratings: 
  • Scopus rating (2017): CiteScore 3.7 SJR 0.44 SNIP 1.093
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Safety, Risk, Reliability and Quality, Electrical and Electronic Engineering
Keywords: 85/85 test, Direct chip attachment, Inkjet, interconnections, Reliability
Electronic versions: 

Bibliographical note

EXT="Niittynen, Juha"
EXT="Myllymäki, Sami"
EXT="Kunnari, Esa"

Source: Scopus
Source ID: 85025617207

Research output: Contribution to journalArticleScientificpeer-review

Quench Protection Study of the Eurocircol 16 T cosθ Dipole for the Future Circular Collider (FCC)

After Large Hadron Collider will be turned off, a new, more energetic machine will be needed in order to explore unknown regions of the high-energy physics. For this reason, the project Future Circular Collider (FCC) has started, with the goal of developing a 100-km-circumference collider of 50 TeV proton beams. The Eurocircol collaboration is part of the FCC study under the European Community leadership, and it aims to develop a conceptual design of FCC till 2019. One of the main targets is to design a bending dipole able to reach 16 T operation magnetic field, in order to accomplish the size and energy constraints. Such a magnetic field can be reached using Nb3Sn conductors. One option under exploration is the Cosθ dipole, by INFN of Milano and Genova. Because of the high stored energy and the large current densities due to the conductor performances, quench protection is one of the most challenging aspects of the design. In this paper, the quench protection of the cosθ design is presented. A standard quench protection study is accompanied by a less conservative study which includes ac effects on the power dissipation inside the coils and on the magnet inductance, in order to not exclude preventively more convenient designs, and to develop a more performing magnet as possible.

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, Università degli Studi di Milano, Istituto Nazionale Di Fisica Nucleare, Frascati
Contributors: Marinozzi, V., Bellomo, G., Caiffi, B., Fabbricatore, P., Farinon, S., Salmi, T., Sorbi, M., Stenvall, A., Volpini, G.
Publication date: 1 Jun 2017
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 27
Issue number: 4
Article number: 4702505
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2017): CiteScore 1.45 SJR 0.408 SNIP 0.962
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: accelerator dipoles, Quench protection, superconducting magnets
Source: Scopus
Source ID: 85014850365

Research output: Contribution to journalArticleScientificpeer-review

Considerations on a Cost Model for High-Field Dipole Arc Magnets for FCC

In the frame of the European circular collider, a conceptual design study for a post-Large Hadron Collider research infrastructure based on an energy-frontier 100 TeV circular hadron collider, a cost model for the dipole arc magnets is being developed. This paper presents an analysis of the different cost drivers for these magnets, in particular for what concerns magnet aperture, the nature and extent of grading, margin and operating temperature.

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, IRFM, CIEMAT, Università degli Studi di Milano, Istituto Nazionale Di Fisica Nucleare, Frascati
Contributors: Schoerling, D., Durante, M., Lorin, C., Martinez, T., Ruuskanen, J., Salmi, T., Sorbi, M., Tommasini, D., Toral, F.
Publication date: 1 Jun 2017
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 27
Issue number: 4
Article number: 4003105
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2017): CiteScore 1.45 SJR 0.408 SNIP 0.962
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: cost optimization, FCC, Nb Sn multifilamentary superconductor, Superconducting magnets
Source: Scopus
Source ID: 85014853660

Research output: Contribution to journalArticleScientificpeer-review

The 16 T Dipole Development Program for FCC

A key challenge for a future circular collider (FCC) with centre-of-mass energy of 100 TeV and a circumference in the range of 100 km is the development of high-field superconducting accelerator magnets, capable of providing a 16 T dipolar field of accelerator quality in a 50 mm aperture. This paper summarizes the strategy and actions being undertaken in the framework of the FCC 16 T Magnet Technology Program and the Work Package 5 of the EuroCirCol.

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, Istituto Nazionale Di Fisica Nucleare, Frascati, University of Twente, French Atomic Energy Commission (CEA) Saclay, Environment and Technology, KEK, Universite de Geneve
Contributors: Tommasini, D., Auchmann, B., Bajas, H., Bajko, M., Ballarino, A., Bellomo, G., Benedikt, M., Bermudez, S. I., Bordini, B., Bottura, L., Buzio, M., Dhalle, M., Durante, M., De Rijk, G., Fabbricatore, P., Farinon, S., Ferracin, P., Gao, P., Lackner, F., Lorin, C., Marinozzi, V., Martinez, T., Munilla, J., Ogitsu, T., Ortwein, R., Perez, J., Prioli, M., Rifflet, J. M., Rochepault, E., Russenschuck, S., Salmi, T., Savary, F., Schoerling, D., Segreti, M., Senatore, C., Sorbi, M., Stenvall, A., Todesco, E., Toral, F., Verweij, A. P., Volpini, G., Wessel, S., Wolf, F.
Publication date: 1 Jun 2017
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 27
Issue number: 4
Article number: 4000405
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2017): CiteScore 1.45 SJR 0.408 SNIP 0.962
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: 16 T, FCC, NbSn, superconducting
Source: Scopus
Source ID: 85012994421

Research output: Contribution to journalArticleScientificpeer-review

Catalytic Activity of AuCu Clusters on MgO(100): Effect of Alloy Composition for CO Oxidation

Density functional simulations have been performed for Au7Cu23 and Au23Cu7 clusters on MgO(100) supports to probe their catalytic activity for CO oxidation. The adsorption of reactants, O2 and CO, and potential O2 dissociation have been investigated in detail by tuning the location of vacancies (F-center, V-center) in MgO(100). The total charge on Au7Cu23 and Au23Cu7 is negative on all supports, regardless of the presence of vacancies, but the effect is significantly amplified on the F-center. Au7Cu23/MgO(100) and Au23Cu7/MgO(100) with an F-center are the only systems to bind O2 more strongly than CO. In each case, O2 can be effectively activated upon adsorption and dissociated to 2 × O atoms. The different reaction paths based on the Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms for CO oxidation have been explored on the Au7Cu23 and Au23Cu7 clusters on F-centers, and the results are compared with the previous findings for Au15Cu15. Overall, the reaction barriers are small, but the changes in the Au:Cu ratio tune the reactant adsorption energies and sites considerably, showing also varying selectivity for CO and O2. The microkinetic model built on the basis of the above results shows a pronounced CO2 production rate at low temperature for the clusters on F-centers.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, Research group: Materials and Molecular Modeling, COMP Centre of Excellence, Department of Applied Physics, Aalto University, Aalto University, Norwegian Univ. of Sci. and Technol.
Contributors: Ma, L., Laasonen, K., Akola, J.
Number of pages: 11
Pages: 10876-10886
Publication date: 25 May 2017
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry C
Volume: 121
Issue number: 20
ISSN (Print): 1932-7447
Ratings: 
  • Scopus rating (2017): CiteScore 7.9 SJR 2.135 SNIP 1.133
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Energy(all), Surfaces, Coatings and Films, Physical and Theoretical Chemistry
URLs: 
Source: Scopus
Source ID: 85020757142

Research output: Contribution to journalArticleScientificpeer-review

Geometric Structure and Chemical Ordering of Large AuCu Clusters: A Computational Study

Understanding the structure and composition of nanosized gold-copper (AuCu) clusters is crucial for designing an effective AuCu catalyst. Global optimization of AuCu clusters using atomistic force fields is a viable solution for clusters with at least a few nm sizes, because of its fast computation. Here we develop an atomistic many-body potential for AuCu on the basis of the second-moment approximation to the tight-binding model. We show that our potential is in good agreement with density-functional theory calculations, and use it to study the structure and chemical ordering of clusters of sizes up to ∼4 nm by means of global optimization searches. We show that the clusters present a surface enrichment in Au, while subsurface and central sites are enriched in Cu. Surface enrichment in Au and center enrichment in Cu are stronger in icosahedra. Surface Cu atoms prefer terrace sites on (111) facets. Both atomistic and DFT calculations show that L10 and L12 ordered phases are not favorable, even at their ideal compositions for these sizes, because of the tendency of Au to surface segregation. The stability range of icosahedral structures is wider in AuCu nanoalloys than in Au and Cu pure clusters.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Physics, COMP Centre of Excellence, Department of Applied Physics, Aalto University, Aalto University, Università di Genova
Contributors: Goh, J., Akola, J., Ferrando, R.
Number of pages: 8
Pages: 10809-10816
Publication date: 25 May 2017
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry C
Volume: 121
Issue number: 20
ISSN (Print): 1932-7447
Ratings: 
  • Scopus rating (2017): CiteScore 7.9 SJR 2.135 SNIP 1.133
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Energy(all), Physical and Theoretical Chemistry, Surfaces, Coatings and Films
Source: Scopus
Source ID: 85016919329

Research output: Contribution to journalArticleScientificpeer-review

Photoinduced Electron Injection from Zinc Phthalocyanines into Zinc Oxide Nanorods: Aggregation Effects

Phthalocyanines (Pc) are well-known light-harvesting compounds. However, despite the tremendous efforts on phthalocyanine synthesis, the achieved energy conversion efficiencies for Pc-based dye-sensitized solar cells are moderate. To cast light on the factors reducing the conversion efficiency, we have undertaken a time-resolved spectroscopy study of the primary photoinduced reactions at a semiconductor-Pc interface. ZnO nanorods were chosen as a model semiconductor substrate with enhanced specific surface area. The use of a nanostructured oxide surface allows to extend the semiconductor-dye interface with a hole transporting layer (spiro-MeOTAD) in a controlled way, making the studied system closer to a solid-state dye-sensitized solar cell. Four zinc phthalocyanines are compared in this study. The compounds are equipped with bulky peripheral groups designed to reduce the self-aggregation of the Pcs. Almost no signs of aggregation can be observed from the absorption spectra of the Pcs assembled on a ZnO surface. Nevertheless, the time-resolved spectroscopy indicates that there are inter-Pc charge separation-recombination processes in the time frame of 1-100 ps. This may reduce the electron injection efficiency into the ZnO by more than 50%, pointing out to a remaining aggregation effect. Surprisingly, the electron injection time does not correlate with the length of the linker connecting the Pc to ZnO. A correlation between the electron injection time and the "bulkiness" of the peripheral groups was observed. This correlation is further discussed with the use of computational modeling of the Pc arrangements on the ZnO surface. (Figure Presented).

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Research group: Chemistry & Advanced Materials, Instituto Madrileño de Estudios Avanzados (IMDEA)-Nanociencia, Universidad Autónoma de Madrid, Mersin University, South-Ukrainian National Pedagogical University
Contributors: Virkki, K., Hakola, H., Urbani, M., Tejerina, L., Ince, M., Martínez-Díaz, M. V., Torres, T., Golovanova, V., Golovanov, V., Tkachenko, N. V.
Number of pages: 12
Pages: 9594-9605
Publication date: 4 May 2017
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry C
Volume: 121
Issue number: 17
ISSN (Print): 1932-7447
Ratings: 
  • Scopus rating (2017): CiteScore 7.9 SJR 2.135 SNIP 1.133
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Energy(all), Surfaces, Coatings and Films, Physical and Theoretical Chemistry
Source: Scopus
Source ID: 85020915273

Research output: Contribution to journalArticleScientificpeer-review

Halogen bonding stabilizes a cis-azobenzene derivative in the solid state: A crystallographic study

Crystals of trans- and cis-isomers of a fluorinated azobenzene derivative have been prepared and characterized by single-crystal X-ray diffraction. The presence of F atoms on the aromatic core of the azobenzene increases the lifetime of the metastable cis-isomer, allowing single crystals of the cis-azobenzene to be grown. Structural analysis on the cis-azobenzene, complemented with density functional theory calculations, highlights the active role of the halogen-bond contact (N...I synthon) in promoting the stabilization of the cis-isomer. The presence of a long aliphatic chain on the azobenzene unit induces a phase segregation that stabilizes the molecular arrangement for both the trans- and cis-isomers. Due to the rarity of cis-azobenzene crystal structures in the literature, our paper makes a step towards understanding the role of non-covalent interactions in driving the packing of metastable azobenzene isomers. This is expected to be important in the future rational design of solid-state, photoresponsive materials based on halogen bonding. We show by single-crystal X-ray diffraction studies and computational analysis that halogen bonding can stabilize a metastable cis-azobenzene derivative in the solid state.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Research group: Supramolecular photochemistry, Research group: Chemistry & Advanced Materials, Politecnico di Milano, Aalto University
Contributors: Saccone, M., Siiskonen, A., Fernandez-Palacio, F., Priimägi, A., Terraneo, G., Resnati, G., Metrangolo, P.
Number of pages: 7
Pages: 227-233
Publication date: 1 Apr 2017
Peer-reviewed: Yes

Publication information

Journal: ACTA CRYSTALLOGRAPHICA SECTION B : STRUCTURAL SCIENCE, CRYSTAL ENGINEERING AND MATERIALS
Volume: 73
Issue number: 2
ISSN (Print): 2052-5192
Ratings: 
  • Scopus rating (2017): CiteScore 4.54 SJR 1.654 SNIP 1.602
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Metals and Alloys, Materials Chemistry
Keywords: azobenzene, halogen bonding, isomerization
Source: Scopus
Source ID: 85017113549

Research output: Contribution to journalArticleScientificpeer-review

Simulation studies of DFB laser longitudinal structures for narrow linewidth emission

The paper presents simulation studies targeting high-power narrow-linewidth emission from semiconductor distributed feedback (DFB) lasers. The studies contain analytic and numerical calculations of emission linewidth, side mode suppression ratio and output power for DFB lasers without phase shifts and with 1 × λ/ 4 and 2 × λ/ 8 phase shifts, taking into account the grating and facets reflectivities, the randomness of the spontaneous emission and the longitudinal photon and carrier density distributions in the laser cavity. Single device structural parameter optimization is generally associated with a trade-off between achieving a narrow linewidth and a high output power. Correlated optimization of multiple structural parameters enables the evaluation of achievable ranges of narrow linewidth and high power combinations. Devices with long cavities and low grating coupling coefficients, κ (keeping κL values below the levels that promote re-broadening), with AR-coated facets and with a distributed phase-shift have the flattest longitudinal photon and carrier density distributions. This flatness enables stable single-longitudinal-mode operation with high side-mode-suppression ratio up to high injection current densities, which facilitates narrow linewidths and high output powers. The results reported in the paper indicate that Master-Oscillator Power-Amplifier laser structures are needed for achieving W-level high-powers with sub-MHz linewidths because most single-cavity DFB laser structural variations that reduce the linewidth also limit the achievable output power in single-mode operation.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Research group: Semiconductor Technology and Applications
Contributors: Virtanen, H., Uusitalo, T., Dumitrescu, M.
Number of pages: 13
Publication date: 23 Mar 2017
Peer-reviewed: Yes

Publication information

Journal: Optical and Quantum Electronics
Volume: 49
Issue number: 4
Article number: 160
ISSN (Print): 0306-8919
Ratings: 
  • Scopus rating (2017): CiteScore 1.8 SJR 0.353 SNIP 0.631
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Electrical and Electronic Engineering
Keywords: Distributed feedback laser, High power, Narrow linewidth
Electronic versions: 
URLs: 
Source: Scopus
Source ID: 85016097411

Research output: Contribution to journalArticleScientificpeer-review

Effect of the addition of Al2O3, TiO2 and ZnO on the thermal, structural and luminescence properties of Er3+-doped phosphate glasses

Er-doped phosphate glasses were fabricated by melt-quenching technique. The changes in their thermal, structural and luminescence properties with the addition of Al2O3, TiO2 or ZnO were studied. Physical and thermal properties were investigated through density measurement and differential thermal analysis. Structural characterization was performed using the Raman and Infrared spectroscopy. In order to study the influence of the composition on the luminescence properties of the glasses, the refractive index, the luminescence spectra and the lifetime values were measured. The results show that with the addition of Al2O3 and TiO2 the phosphate network becomes more connected increasing the glass transition temperature, whereas the addition of ZnO does not show significant changes in the optical, thermal and structural properties but it leads to a larger emission cross-section at 1540 nm as compared to the other glasses. As the site of the Er3+ is not strongly affected by the change in the glass composition, we think that the emission properties of the glasses depend on the glass structure connectivity, which has an impact on the Er3+ ions solubility.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Faculty of Biomedical Sciences and Engineering, Research group: Biomaterials and Tissue Engineering Group, Politecnico di Torino, Istituto Superiore Mario Boella, CSMFO Lab.
Contributors: Lopez-Iscoa, P., Petit, L., Massera, J., Janner, D., Boetti, N. G., Pugliese, D., Fiorilli, S., Novara, C., Giorgis, F., Milanese, D.
Number of pages: 8
Pages: 161-168
Publication date: 15 Mar 2017
Peer-reviewed: Yes

Publication information

Journal: Journal of Non-Crystalline Solids
Volume: 460
ISSN (Print): 0022-3093
Ratings: 
  • Scopus rating (2017): CiteScore 4 SJR 0.722 SNIP 1.178
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Ceramics and Composites, Condensed Matter Physics, Materials Chemistry
Keywords: Er luminescence property, Infrared spectroscopy, Phosphate glass, Raman spectroscopy
Source: Scopus
Source ID: 85010441113

Research output: Contribution to journalArticleScientificpeer-review

Chip-by-chip configurable interconnection using digital printing techniques

Printed electronics technologies add new fabrication concepts to the classical set of microelectronic processes. Among these, the use of digital printing techniques such as inkjet permits the deposition of materials on top of preexisting substrates without any mask. This allows individual personalization of electronic circuits. Different proposals have been made to make use of such a property: (1) wiring new metallic layers on top of circuits to build programmable logic array-like circuits, (2) programming OTP ROM like memories, and (3) building inkjet-configurable gate arrays. The capability of building an individual circuit with technological steps simpler than photolithographic ones opens a concept similar to the successful field programmable gate array. Although nowadays the process resolution is still low, it can quickly evolve to higher wiring densities and therefore permit a greater level of transistor integration. In this paper, we propose a new structure to realize the connections only by deposition of conductive dots oriented to optimize the area needed to implement the drop-on-demand (DoD) wiring at circuit level. One important feature of this structure is that it minimizes the amount of printed material required for the connection thereby reducing failures often seen with DoD printing techniques for conductive lines. These structures have been validated by two different DoD technologies: inkjet and superfine jet, and have been compared to mask-based photolithography technology with promising results.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electronics and Communications Engineering, Research group: Laboratory for Future Electronics, Universitat Autònoma de Barcelona, Centre for Process Innovation (CPI), A UK Based OSC Materials Company, IMB-CNM (CSIC)
Contributors: Mashayekhi, M., Winchester, L., Laurila, M., Mäntysalo, M., Ogier, S., Terés, L., Carrabina, J.
Publication date: 6 Mar 2017
Peer-reviewed: Yes

Publication information

Journal: Journal of Micromechanics and Microengineering
Volume: 27
Issue number: 4
Article number: 045009
ISSN (Print): 0960-1317
Ratings: 
  • Scopus rating (2017): CiteScore 3.7 SJR 0.554 SNIP 1.015
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Mechanics of Materials, Mechanical Engineering, Electrical and Electronic Engineering
Keywords: digital circuits, digital printing, drop-on-demand, inkjet, inkjet configurable gate array, interconnection, printed electronics
Electronic versions: 
Source: Scopus
Source ID: 85016467042

Research output: Contribution to journalArticleScientificpeer-review

Combination of E-jet and inkjet printing for additive fabrication of multilayer high-density RDL of silicon interposer

The additive nature and high resolution of electrohydrodynamic inkjet (E-jet) printing can be utilized for manufacturing micrometer scale conductive tracks such as those required in the high-density redistribution layers (RDLs) of silicon interposers used in electronics packaging for 3-D integration. Compared to the current lithographic fabrication method, this approach promises to increase the customizability of the process and reduce the amount of waste materials, thereby lowering the costs and the environmental impact of the manufacturing process. In this paper, multilayer interdigitated capacitor and meander resistor structures with 5/5 μm conductor width/spacing are used to demonstrate the feasibility of E-jet printing of high-density multilayer RDLs. A sheet resistance of 28.5 Ω/square was achieved for the first metallization layer (MET1) conductors and 313.2 7Ω/square for the MET2 conductors. The thickness of the conductors was 6.9 μm for MET1 and 5.4 μm for MET2.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electronics and Communications Engineering, Research group: Laboratory for Future Electronics, Research group: Wireless Communications and Positioning
Contributors: Laurila, M., Khorramdel, B., Mäntysalo, M.
Number of pages: 8
Pages: 1217-1224
Publication date: 1 Mar 2017
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Electron Devices
Volume: 64
Issue number: 3
ISSN (Print): 0018-9383
Ratings: 
  • Scopus rating (2017): CiteScore 4.7 SJR 0.839 SNIP 1.485
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering
Keywords: 3-D integration, additive manufacturing, electrohydrodynamic inkjet (E-jet) printing, electronics packaging, high-density printing, printed electronics, silicon interposer
Source: Scopus
Source ID: 85009833867

Research output: Contribution to journalArticleScientificpeer-review

Very high dose electron irradiation effects on photoluminescence from GaInNAs/GaAs quantum wells grown by molecular beam epitaxy

The effects of 7 MeV electron irradiation at very high doses of 2×1017 and 1.5×1018electrons/cm2 and subsequent rapid thermal annealing on photoluminescence from a strain-compensated GaInAsN/GaAsN/GaAs quantum well structure are investigated. A large additional blueshift of photoluminescence has been observed from the lower-dose irradiated sample as compared to the non-irradiated one when annealed after the irradiation. This additional blueshift will become considerably reduced by an ageing effect, which occurs already at room temperature. The mechanism causing the additional blueshift of photoluminescence and its reduction is qualitatively assigned to metastable complex defects promoted by electron irradiation in the nitrogen containing layers. No such additional blueshift of photoluminescence under the thermal treatment has been observed in the higher-dose irradiated sample.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, National Institute for Research and Development in Microtechnologies Romania, Faculty of Exact Sciences and Engineering, Hyperion University
Contributors: Pavelescu, E. M., Bălţăţeanu, N., Spânulescu, S. I., Arola, E.
Number of pages: 5
Pages: 361-365
Publication date: 1 Feb 2017
Peer-reviewed: Yes

Publication information

Journal: Optical Materials
Volume: 64
ISSN (Print): 0925-3467
Ratings: 
  • Scopus rating (2017): CiteScore 3.7 SJR 0.592 SNIP 1.054
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: Dilute nitrides, Electron irradiation, Photoluminescence

Bibliographical note

EXT="Pavelescu, E. M."

Source: Scopus
Source ID: 85008334984

Research output: Contribution to journalArticleScientificpeer-review

Architectures and codecs for real-time light field streaming

Light field 3D displays represent a major step forward in visual realism, providing glasses-free spatial vision of real or virtual scenes. Applications that capture and process live imagery have to process data captured by potentially tens to hundreds of cameras and control tens to hundreds of projection engines making up the human perceivable 3D light field using a distributed processing system. The associated massive data processing is difficult to scale beyond a specific number and resolution of images, limited by the capabilities of the individual computing nodes. The authors therefore analyze the bottlenecks and data flow of the light field conversion process and identify possibilities to introduce better scalability. Based on this analysis they propose two different architectures for distributed light field processing. To avoid using uncompressed video data all along the processing chain, the authors also analyze how the operation of the proposed architectures can be supported by existing image/video codecs.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing, Research group: 3D MEDIA, Holografika, Nokia
Contributors: Kovács, P. T., Zare, A., Balogh, T., Bregovic, R., Gotchev, A.
Publication date: 1 Jan 2017
Peer-reviewed: Yes

Publication information

Journal: Journal of Imaging Science and Technology
Volume: 61
Issue number: 1
Article number: 010403
ISSN (Print): 1062-3701
Ratings: 
  • Scopus rating (2017): CiteScore 0.59 SJR 0.237 SNIP 0.718
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Chemistry(all), Atomic and Molecular Physics, and Optics, Computer Science Applications
Source: Scopus
Source ID: 85016298177

Research output: Contribution to journalArticleScientificpeer-review

Non-destructive and wireless monitoring of biodegradable polymers

A method for monitoring changes in biodegradable polymers during hydrolysis is proposed. This wireless and non-destructive method is based on inductively coupled passive resonance sensors embedded in the polymer shell. In this study, we prepared specimens using two poly(lactide-co-glycolide) copolymers possessing different degradation profiles. The copolymer embedded sensors were immersed in buffer solution and their resonance features were compared with periodically performed conventional polymer characterization methods. A clear difference was noticed in the wirelessly measured signals between the two tested copolymer materials. Also the reference methods showed clear differences between the degradation profiles of the copolymers. The wirelessly measured signals are likely to correlate to the structural changes in the materials during the hydrolysis. In the future, this technique could be used in the laboratory to provide easy-to-access in situ information about the polymers. Even the state of biodegradable polymer implants could be wirelessly monitored.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Faculty of Biomedical Sciences and Engineering, Research area: Microsystems, Research group: Sensor Technology and Biomeasurements (STB), Research group: Biomaterials and Tissue Engineering Group, BioMediTech
Contributors: Salpavaara, T., Hänninen, A., Antniemi, A., Lekkala, J., Kellomäki, M.
Pages: 1018-1025
Publication date: 2017
Peer-reviewed: Yes

Publication information

Journal: Sensors and Actuators B: Chemical
Volume: 251
ISSN (Print): 0925-4005
Ratings: 
  • Scopus rating (2017): CiteScore 9.3 SJR 1.406 SNIP 1.453
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Instrumentation, Condensed Matter Physics, Surfaces, Coatings and Films, Metals and Alloys, Materials Chemistry, Electrical and Electronic Engineering
Keywords: Biodegradable polymers, Passive resonance sensor, Poly(lactide-co-glycolide), Telemetry, Wireless monitoring
Electronic versions: 
Source: Scopus
Source ID: 85020132649

Research output: Contribution to journalArticleScientificpeer-review

Optimization of convectively cooled heat sinks

Many factors of heat sink, such as its size and mass, component locations, number of fins, and fan power affect heat transfer. Owing to the opposite effects of these factors on heat sink maximum temperature, we have now a multi-objective optimization problem. A typical optimization case consists of hundreds of heat sink temperature field evaluations, which would be impractical to do with CFD. Instead, we propose to combine analytical results of convection and numerical solution of conduction to address these so-called conjugated heat transfer problems. We solve heat conduction in a solid numerically using the finite volume method and tackle convection with the analytical equation of forced convection in a parallel plate channel.This model is suitable for forced and natural convection heat sinks, and we have verified its validity by comparing its results to measured data and CFD calculations. We use the model to improve two industrial examples, using a multi-objective version of the particle swarm optimization (PSO) algorithm. The first example is a forced convection heat sink composed of nine heat generating components at the base plate, and the other is a natural convection case with two components. In both cases, mass is minimized; the other criterion is maximum temperature for the forced convection case and heat sink outer volume for the natural convection case. Our method is many orders of magnitude faster than CFD. Additionally, we provide some LES results of pin fins with natural convection for further use in similar optimizations.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Research group: Bio- and Circular Economy, Mechanical Engineering and Industrial Systems
Contributors: Lampio, K., Karvinen, R.
Pages: 473-479
Publication date: 2017
Peer-reviewed: Yes

Publication information

Journal: Microelectronics Reliability
Volume: 79
ISSN (Print): 0026-2714
Ratings: 
  • Scopus rating (2017): CiteScore 1.52 SJR 0.388 SNIP 0.907
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: Fin array, Forced convection, Heat sink, Multi-objective optimization, Natural convection, Pin fins
Source: Scopus
Source ID: 85020690970

Research output: Contribution to journalArticleScientificpeer-review

Solar Irradiation Independent Expression for Photovoltaic Generator Maximum Power Line

In order to enhance maximum power point tracking (MPPT) speed of photovoltaic generators (PVGs) upon fast irradiation changes, maximum power line (MPL)-based control is often used. MPL is a curve, linking all possible MPP coordinates for a given temperature. In the literature so far, PVG MPL was either assumed linear, which is inaccurate for all irradiation levels, or possessed photocurrent dependence, requiring real-time estimation of the latter. In this letter, an irradiation-independent explicit expression for PVG MPL is derived, valid for all practical irradiation levels, thus allowing real-time implementation without the need of photocurrent estimation.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electrical Energy Engineering, Research group: Power electronics
Contributors: Kolesnik, S., Sitbon, M., Lineykin, S., Batzelis, E., Papathanassiou, S., Suntio, T., Kuperman, A.
Pages: 1416-1420
Publication date: 2017
Peer-reviewed: Yes

Publication information

Journal: IEEE Journal of Photovoltaics
Volume: 7
Issue number: 5
ISSN (Print): 2156-3381
Ratings: 
  • Scopus rating (2017): CiteScore 7.9 SJR 1.214 SNIP 1.499
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Equivalent circuits, Estimation, maximum power line (MPL), Maximum power point tracking (MPPT), Multiprotocol label switching, Photoconductivity, photovoltaic generator (PVG), Photovoltaic systems, Radiation effects, single diode model
Electronic versions: 
Source: Scopus
Source ID: 85023754880

Research output: Contribution to journalArticleScientificpeer-review

Mechanical behavior of a 16 T FCC dipole magnet during a quench

Future accelerator magnets are pushed to their limits in terms of magnetic field, mechanical strength and from the quench protection point of view. This forces the magnet designers to re-think the quench modelling. One issue that has not so far been largely explored is the mechanical behaviour of the superconducting coils during a quench. This can cause limitations to the design of high field accelerator magnets. This paper focuses on mechanical behavior in the event of a quench of a Nb3Sn 16 T dipole magnet currently developed in the framework of the EuroCirCol project in view of the Future Circular Collider conceptual design study. The thermo-mechanical analysis is performed through finite element modeling. The analysis takes into account the Lorentz force and the thermal stress due to the non-uniform temperature distribution in the winding during a quench.

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
Contributors: Zhao, J., Stenvall, A., Salmi, T., Gao, Y., Lorin, C.
Publication date: 2017
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 27
Issue number: 6
Article number: 4004407
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2017): CiteScore 1.45 SJR 0.408 SNIP 0.962
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: accelerator magnet, Computational modeling, finite element analysis, Lorentz forces, Magnetic flux, Magnetomechanical effects, Magnetosphere, Magnetostatics, quench, Stress, Superconducting magnets, thermal stress

Bibliographical note

INT=eee,"Zhao, Junjie"

Source: Scopus
Source ID: 85021962608

Research output: Contribution to journalArticleScientificpeer-review

High-resolution coded-aperture design for compressive X-ray tomography using low resolution detectors

One of the main challenges in Computed Tomography (CT) is obtaining accurate reconstructions of the imaged object while keeping a low radiation dose in the acquisition process. In order to solve this problem, several researchers have proposed the use of compressed sensing for reducing the amount of measurements required to perform CT. This paper tackles the problem of designing high-resolution coded apertures for compressed sensing computed tomography. In contrast to previous approaches, we aim at designing apertures to be used with low-resolution detectors in order to achieve super-resolution. The proposed method iteratively improves random coded apertures using a gradient descent algorithm subject to constraints in the coherence and homogeneity of the compressive sensing matrix induced by the coded aperture. Experiments with different test sets show consistent results for different transmittances, number of shots and super-resolution factors.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing
Contributors: Mojica, E., Pertuz, S., Arguello, H.
Pages: 103-109
Publication date: 2017
Peer-reviewed: Yes

Publication information

Journal: Optics Communications
Volume: 404
ISSN (Print): 0030-4018
Ratings: 
  • Scopus rating (2017): CiteScore 3.5 SJR 0.614 SNIP 0.933
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Physical and Theoretical Chemistry, Electrical and Electronic Engineering
Keywords: Coded apertures, Compressive sensing, Computed tomography, Super-resolution
Source: Scopus
Source ID: 85021667000

Research output: Contribution to journalArticleScientificpeer-review

Three-color vector nematicon

Light localization via reorientation in nematic liquid crystals supports multi-component optical spatial solitons, i.e., vector nematicons. By launching three optical beams of different wavelengths and the same input polarization in a bias-free planar cell, we demonstrate a three-color vector nematicon which is self-trapped thanks to its incoherent nature.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Photonics, Politechnika Warszawska, Univ Roma Tre, Roma Tre University, Dept Elect Engn, NooEL, University “Roma Tre”, Aerosol Physics Laboratory
Contributors: Laudyn, U. A., Kwaśny, M., Karpierz, M. A., Assanto, G.
Number of pages: 3
Pages: 36-38
Publication date: 2017
Peer-reviewed: Yes

Publication information

Journal: Photonics Letters of Poland
Volume: 9
Issue number: 2
ISSN (Print): 2080-2242
Ratings: 
  • Scopus rating (2017): CiteScore 0.9 SJR 0.25 SNIP 0.446
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials
Electronic versions: 
Source: Scopus
Source ID: 85021814168

Research output: Contribution to journalArticleScientificpeer-review

Two cations, two mechanisms: Interactions of sodium and calcium with zwitterionic lipid membranes

Adsorption of metal cations onto a cellular membrane changes its properties, such as interactions with charged moieties or the propensity for membrane fusion. It is, however, unclear whether cells can regulate ion adsorption and the related functions via locally adjusting their membrane composition. We employed fluorescence techniques and computer simulations to determine how the presence of cholesterol - a key molecule inducing membrane heterogeneity - affects the adsorption of sodium and calcium onto zwitterionic phosphatidylcholine bilayers. We found that the transient adsorption of sodium is dependent on the number of phosphatidylcholine head groups, while the strong surface binding of calcium is determined by the available surface area of the membrane. Cholesterol thus does not affect sodium adsorption and only plays an indirect role in modulating the adsorption of calcium by increasing the total surface area of the membrane. These observations also indicate how lateral lipid heterogeneity can regulate various ion-induced processes including adsorption of peripheral proteins, nanoparticles, and other molecules onto membranes.

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
Contributors: Javanainen, M., Melcrová, A., Magarkar, A., Jurkiewicz, P., Hof, M., Jungwirth, P., Martinez-Seara, H.
Number of pages: 4
Pages: 5380-5383
Publication date: 2017
Peer-reviewed: Yes

Publication information

Journal: Chemical Communications
Volume: 53
Issue number: 39
ISSN (Print): 1359-7345
Ratings: 
  • Scopus rating (2017): CiteScore 11.9 SJR 2.555 SNIP 1.127
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
Electronic versions: 
Source: Scopus
Source ID: 85021689400

Research output: Contribution to journalArticleScientificpeer-review

Electrical Contacts in SOI MEMS Using Aerosol Jet Printing

In this study, an additive method to make electrical contacts in SOI MEMS devices with aerosol jet printing is introduced. Small grooves were etched to the frame of MEMS accelerometer in the same step with the active structure release. Aluminum ink was jetted to the trenches in wafer-level to bridge the device layer to the handle wafer with the minimum amount of material. After subsequent annealing ohmic contacts between p-type device layer and p-type handle silicon were verified by I-V measurements. The via resistance less than 4 Y per via is measured. The method demonstrated in this work provides simple and low-cost approach for SOI handle contact where additional packaging of wafer process steps can be avoided.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electronics and Communications Engineering, Research group: Laboratory for Future Electronics, Murata Electronics Oy
Contributors: Khorramdel, B., Torkkeli, A., Mäntysalo, M.
Pages: 34-40
Publication date: 2017
Peer-reviewed: Yes
Early online date: 19 Oct 2017

Publication information

Journal: IEEE Journal of the Electron Devices Society
Volume: 6
ISSN (Print): 2168-6734
Ratings: 
  • Scopus rating (2017): CiteScore 4.7 SJR 1.016 SNIP 1.465
Original language: English
ASJC Scopus subject areas: Biotechnology, Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering
Keywords: additive manufacturing., aerosol jet printing, Aerosols, Cavity resonators, Electrical resistance measurement, Ink, inkjet printing, microelectromechanical systems (MEMS), Micromechanical devices, Printing, silicon on insulator (SOI), Silicon-on-insulator
Source: Scopus
Source ID: 85032682442

Research output: Contribution to journalArticleScientificpeer-review

Photophysical properties of porphyrin dimer-single-walled carbon nanotube linked systems

Porphyrin dimers were covalently grafted onto electron-accepting single-walled carbon nanotube (SWNT) sidewalls by direct aryl radical addition reaction with an m-or p-phenylene linker with the help of p-p interaction between the porphyrins. A splitting of the porphyrin Soret band and DFT calculations supported the selective formation of the porphyrin dimers on the sidewall of SWNTs. Photoexcitation of the porphyrin dimers on the SWNT resulted in the formation of the exciplex state, which directly decayed to the ground state without yielding the complete charge-separated state. Lifetimes of the porphyrin dimer-SWNT exciplex were longer than that of a porphyrin monomer-SWNT exciplex due to the stabilization by p-electron interaction over two porphyrin rings. In addition, the weaker electronic coupling through the meta-linkage than the para-one may be responsible for the exciplex lifetime of the porphyrin dimer-SWNT with the m-phenylene linker (49 ps) longer than that with the p-phenylene one (24 ps). The results obtained here provide the basic information on the effect of the donor dimerization on the photodynamic behavior of the exciplex state in donor-acceptor linked systems. [Figure presented]

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Chemistry and Bioengineering, Research group: Chemistry & Advanced Materials, Kyoto Women's University
Contributors: Baek, J., Umeyama, T., Mizuno, S., Tkachenko, N. V., Imahori, H.
Publication date: 2017
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry C
Volume: 121
Issue number: 39
ISSN (Print): 1932-7447
Ratings: 
  • Scopus rating (2017): CiteScore 7.9 SJR 2.135 SNIP 1.133
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Energy(all), Physical and Theoretical Chemistry, Surfaces, Coatings and Films
Source: Scopus
Source ID: 85032629899

Research output: Contribution to journalArticleScientificpeer-review

Adaptive multiresolution method for MAP reconstruction in electron tomography

3D image reconstruction with electron tomography holds problems due to the severely limited range of projection angles and low signal to noise ratio of the acquired projection images. The maximum a posteriori (MAP) reconstruction methods have been successful in compensating for the missing information and suppressing noise with their intrinsic regularization techniques. There are two major problems in MAP reconstruction methods: (1) selection of the regularization parameter that controls the balance between the data fidelity and the prior information, and (2) long computation time. One aim of this study is to provide an adaptive solution to the regularization parameter selection problem without having additional knowledge about the imaging environment and the sample. The other aim is to realize the reconstruction using sequences of resolution levels to shorten the computation time. The reconstructions were analyzed in terms of accuracy and computational efficiency using a simulated biological phantom and publically available experimental datasets of electron tomography. The numerical and visual evaluations of the experiments show that the adaptive multiresolution method can provide more accurate results than the weighted back projection (WBP), simultaneous iterative reconstruction technique (SIRT), and sequential MAP expectation maximization (sMAPEM) method. The method is superior to sMAPEM also in terms of computation time and usability since it can reconstruct 3D images significantly faster without requiring any parameter to be set by the user.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Signal Processing, BioMediTech
Contributors: Acar, E., Peltonen, S., Ruotsalainen, U.
Number of pages: 11
Pages: 24-34
Publication date: 1 Nov 2016
Peer-reviewed: Yes

Publication information

Journal: Ultramicroscopy
Volume: 170
ISSN (Print): 0304-3991
Ratings: 
  • Scopus rating (2016): CiteScore 2.82 SJR 1.896 SNIP 1.184
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Instrumentation
Keywords: Adaptive reconstruction, Electron tomography (ET), Maximum a posteriori (MAP) reconstruction, Missing wedge, Multiresolution reconstruction, Regularization parameter
Source: Scopus
Source ID: 84981309739

Research output: Contribution to journalArticleScientificpeer-review

Laser angle-resolved photoemission as a probe of initial state kz dispersion, final-state band gaps, and spin texture of Dirac states in the Bi2 Te3 topological insulator

We have obtained angle-resolved photoemission spectroscopy (ARPES) spectra from single crystals of the topological insulator material Bi2Te3 using a tunable laser spectrometer. The spectra were collected for 11 different photon energies ranging from 5.57 to 6.70 eV for incident light polarized linearly along two different in-plane directions. Parallel first-principles, fully relativistic computations of photointensities were carried out using the experimental geometry within the framework of the one-step model of photoemission. A reasonable overall accord between theory and experiment is used to gain insight into how properties of the initial- and final-state band structures as well as those of the topological surface states and their spin textures are reflected in the laser-ARPES spectra. Our analysis reveals that laser-ARPES is sensitive to both the initial-state kz dispersion and the presence of delicate gaps in the final-state electronic spectrum.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Research area: Computational Physics, Research group: Spectroscopies of Complex Materials, Ames Laboratory, Iowa State University, Northeastern University
Contributors: Ärrälä, M., Hafiz, H., Mou, D., Wu, Y., Jiang, R., Riedemann, T., Lograsso, T. A., Barbiellini, B., Kaminski, A., Bansil, A., Lindroos, M.
Number of pages: 7
Publication date: 27 Oct 2016
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 94
Issue number: 15
Article number: 155144
ISSN (Print): 1098-0121
Ratings: 
  • Scopus rating (2016): CiteScore 3.16 SJR 2.339 SNIP 1.183
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 84994236456

Research output: Contribution to journalArticleScientificpeer-review

Crystallization processes in the phase change material Ge2 Sb2 Te5: Unbiased density functional/molecular dynamics simulations

Three extensive density functional/molecular dynamics simulations of the crystallization of amorphous Ge2Sb2Te5 (460 atoms) [Phys. Rev. B 90, 184109 (2014)PRBMDO1098-012110.1103/PhysRevB.90.184109] have been completed with simulation times of up to 8.2 ns. Together with the results of earlier simulations with and without a crystallite seed, the results clarify essential features of a complicated process. They emphasize, in particular, the stochastic nature of crystallization, the effect of bond orientations and percolation, and the importance of extended simulations of sufficiently large samples. This is particularly evident in describing the role of crystallites that can merge to form larger units or hinder complete crystallization by the formation of grain boundaries. The total pair distribution functions for the final structures are compared with available neutron and x-ray diffraction data.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Singapore University of Technology and Design, COMP Centre of Excellence, Aalto University, Forschungszentrum Jülich (FZJ)
Contributors: Kalikka, J., Akola, J., Jones, R. O.
Publication date: 17 Oct 2016
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 94
Issue number: 13
Article number: 134105
ISSN (Print): 1098-0121
Ratings: 
  • Scopus rating (2016): CiteScore 3.16 SJR 2.339 SNIP 1.183
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 84992161291

Research output: Contribution to journalArticleScientificpeer-review

RF measurements to pinpoint defects in inkjet-printed, thermally and mechanically stressed coplanar waveguides

In this work 10-GHz-band RF measurement and microscopy characterizations were performed on thermally and mechanically long-term-stressed coplanar waveguides (CPW) to observe electrical and mechanical degradation in 1-mm-thick PPO/PPE polymer substrates with inkjet-printed Ag conductors. The structure contained two different CPW geometries in a total of 18 samples with 250/270 μm line widths/gaps and 670/180 μm line widths/gaps. A reliability test was carried out with three sets. In set #1 three 250 μm and three 670 μm lines were stored in room temperature conditions and used as a reference. In set #2 six samples were thermally cycled (TC) for 10,000 cycles, and in set #3 six samples were thermally cycled and bent with 6 mm and 8 mm bending diameters. Thermal stressing was done by cycling the samples in a thermal cycling test chamber operating at 0/100 °C with 15-minutes rise, fall, and dwell times, resulting in a one-hour cycle. The samples were analyzed during cycling breaks using a vector network analyzer (VNA). In addition to optical microscopy, field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) imaging were used to mechanically characterize the structures. The results showed that the line width of 670 μm had better signal performance and better long-term reliability than the line width of 250 μm. In this study, the average limit for proper RF operation was 2500 thermal cycles with both line geometries. The wide CPW lines provided more stable characteristics than the narrow CPW lines for the whole 10,000-cycle duration of the test, combined with repeated bending with a maximum bending radius of 6 mm. A phenomenon of nanoparticle silver protruding from cracks in the print of the bent samples was observed, as well as fracturing of the silver print in the CPW lines.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electronics and Communications Engineering, Microelectronics Research, University of Oulu, Tampere University of Applied Sciences
Contributors: Myllymäki, S., Putaala, J., Hannu, J., Kunnari, E., Mäntysalo, M.
Number of pages: 9
Pages: 142-150
Publication date: 1 Oct 2016
Peer-reviewed: Yes

Publication information

Journal: Microelectronics Reliability
Volume: 65
ISSN (Print): 0026-2714
Ratings: 
  • Scopus rating (2016): CiteScore 1.57 SJR 0.447 SNIP 0.991
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

Bibliographical note

EXT="Kunnari, Esa"
EXT="Myllymäki, Sami"

Source: Scopus
Source ID: 84992618636

Research output: Contribution to journalArticleScientificpeer-review

Photocatalytic and antibacterial properties of ZnO films with different surface topographies on stainless steel substrate

Zinc oxide films with three types of topographies: needle-like and hexagonal rods and flakes, were prepared by hydrothermal synthesis on stainless steel substrates to investigate their photocatalytic and antibacterial properties. The photocatalytic activity was measured with a methylene blue (MB) discoloration test, whereas a method using bioluminescent whole cell bacterial biosensors enabling the constant monitoring of the amount of living cells on the surfaces was used here to study the antibacterial properties. The results showed that photocatalytic activity was clearly influenced by the surface area, which is in turn dependent on the topography. Moreover, it was found that all the examined films decreased notably the amount of Staphylococcus aureus and Escherichia coli on the surfaces. Despite significant differences in the surface areas of the studied samples that led to different zinc dissolution rate in aqueous environment, no notable differences in antibacterial activity between the films with different morphologies could be detected. These results are presented and discussed in this paper.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Materials Science, Research group: Ceramic materials, Department of Chemistry and Bioengineering, Research group: Industrial Bioengineering and Applied Organic Chemistry, VTT Technical Research Centre of Finland
Contributors: Heinonen, S., Kannisto, M., Nikkanen, J., Huttunen-Saarivirta, E., Karp, M., Levänen, E.
Number of pages: 8
Pages: 842-849
Publication date: 1 Oct 2016
Peer-reviewed: Yes

Publication information

Journal: Thin Solid Films
Volume: 616
ISSN (Print): 0040-6090
Ratings: 
  • Scopus rating (2016): CiteScore 3.7 SJR 0.639 SNIP 0.863
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Surfaces and Interfaces, Surfaces, Coatings and Films, Metals and Alloys, Materials Chemistry
Keywords: Antibacterial, Biosensor cell, Hydrothermal synthesis, Photocatalytic activity, Zinc oxide
Source: Scopus
Source ID: 84991648557

Research output: Contribution to journalArticleScientificpeer-review

Thermal effects on the Wigner localization and Friedel oscillations in many-electron nanowires

Thermal effects on the total charge density are studied for a one-dimensional correlated quantum dot by means of the path integral Monte Carlo method. The competition between Friedel and Wigner oscillations at zero temperature is driven by the ratio between the interaction of electronic strength and the kinetic energy of electrons. At the onset of the formation of a Wigner molecule, we show that thermal enhancement of Wigner oscillations occurs in a range of temperatures, which can be observed in the electron density. We further show that low-temperature Friedel oscillations may change to Wigner oscillations upon an increase in the temperature.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, CNR-SPIN, University of Würzburg
Contributors: Kylänpää, I., Cavaliere, F., Ziani, N. T., Sassetti, M., Räsänen, E.
Publication date: 13 Sep 2016
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 94
Issue number: 11
Article number: 115417
ISSN (Print): 1098-0121
Ratings: 
  • Scopus rating (2016): CiteScore 3.16 SJR 2.339 SNIP 1.183
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 84990960683

Research output: Contribution to journalArticleScientificpeer-review

Toward Graphene-Based Passive UHF RFID Textile Tags: A Reliability Study

This paper discusses the fabrication, wireless performance, and reliability of graphene-based passive ultrahigh-frequency radio-frequency identification (RFID) tags on a fabric substrate. The conductive ink comprising functionalized graphene nanoplatelets is deposited directly on a cotton fabric substrate to fabricate the tag antennas. After attaching the chips, the tag performance is evaluated through wireless tag measurements before and after high-humidity conditions, bending, and stretching. Initially, the peak read range of the tag is about 1.6 m, which increases to 3.2 m in 100% humidity conditions. Additionally, after drying, the performance of the tag returns back to normal. In a bending test, the read range of a bent tag decreases below 1 m. Furthermore, the read range of the tag in a nonbended state gradually decreases and is about 1.1 m after 100 bending cycles. According to our measurements, stretching has a serious detrimental effect on these tags and they cannot be considered stretchable. However, these initial results show that this low-cost and eco-friendly graphene RFID tag has a remarkable and unique response to moisture and high reliability in harsh bending conditions. Overall, it also has a strong potential to be used in future wearable sensor applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electronics and Communications Engineering, Research group: Wireless Identification and Sensing Systems Research Group
Contributors: Akbari, M., Virkki, J., Sydänheimo, L., Ukkonen, L.
Number of pages: 3
Pages: 429-431
Publication date: 1 Sep 2016
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Device and Materials Reliability
Volume: 16
Issue number: 3
ISSN (Print): 1530-4388
Ratings: 
  • Scopus rating (2016): CiteScore 3.5 SJR 0.444 SNIP 1.273
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Safety, Risk, Reliability and Quality, Electrical and Electronic Engineering
Keywords: Bending, graphene, humidity, radio-frequency identification (RFID), reliability, stretching, wearable antennas
Source: Scopus
Source ID: 84986587064

Research output: Contribution to journalLetterScientificpeer-review

Generalized slip transformations and air-gap harmonics in field models of electrical machines

In numerical field analysis of steady states of electrical machines, frequency-domain methods are often much faster than time-domain methods. Frequency-domain techniques often involve simplifications that impact their accuracy on harmonic effects due to slotting, saturation, and time harmonics in winding currents. The nature of these inaccuracies and their relationship to air-gap field harmonics is not that well covered in the literature. Correct prediction of air-gap field harmonics can be based on careful use of spectral Dirichlet-to-Neumann mappings and generalized slip transformations. We show how nonzero harmonics in the air-gap fields can be reliably predicted and explain the nature of inaccuracies in certain common steady-state solution techniques.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electrical Engineering, Research area: Electromagnetics
Contributors: Räisänen, V., Suuriniemi, S., Kettunen, L.
Publication date: 1 Sep 2016
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Magnetics
Volume: 52
Issue number: 9
Article number: 8107708
ISSN (Print): 0018-9464
Ratings: 
  • Scopus rating (2016): CiteScore 1.51 SJR 0.653 SNIP 0.949
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering
Keywords: Boundary value problems, Fourier series, harmonics, rotating machines

Bibliographical note

EXT="Räisänen, Ville"

Source: Scopus
Source ID: 84983678510

Research output: Contribution to journalArticleScientificpeer-review

The red, purple and blue modifications of polymeric unsymmetrical hydroxyalkadiynyl-N-arylcarbamate derivatives in Langmuir-Schaefer films

Solid topochemical photopolymerization (STP) of Langmuir-Schaefer films of a new class of unsymmetrical diynes, containing N-arylcarbamate groups in the hydrophobic part and hydroxymethylene groups in the hydrophilic part of the molecules was examined. In addition, the monomeric Langmuir monolayer formation was studied by Brewster angle microscopy and the surface morphology of monomer and polymer films on solid substrates were studied by scanning electron microscopy and atomic force microscopy. Three phases of polydiacetylene (PDA) (red, purple and blue) were observed after UV-light polymerization of above-mentioned films of alcohol diacetylene (DA) derivatives. The substitution of MeO group in the aryl ring substituent by hydrogen atom and the variation of the methylene group number in the hydrophobic part from 5 to 6 changed significantly the result of STP: instead of blue phase PDA observed for diynes with MeO group, the red phase PDA was observed for DA with H-atom from the very beginning of diyne film UV irradiation. For two other diynilic N-arylcarbamates of identical chemical structures except of the substituents in the aryl ring of hydrophobic parts of the molecules, no changes in the efficiency of polymerization or the position and shape of absorption bands were observed. This indicated the formation of the purple phase PDA. For these molecules, the number of methylene groups in hydrophobic and hydrophilic parts of the molecules was 9 and 2, respectively.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Chemistry and Bioengineering, Research group: Supramolecular photochemistry, A. M. Prokhorov General Physics Institute, Russian Academy of Sciences, Åbo Akademi University, St. Petersburg State University, NRC Kurchatov Institute, Russian Acad Sci, Russian Academy of Sciences, Kotelnikov Inst Radio Engn & Elect
Contributors: Alekseev, A., Ihalainen, P., Ivanov, A., Domnin, I., Klechkovskaya, V., Orekhov, A., Lemmetyinen, H., Vuorimaa-Laukkanen, E., Peltonen, J., Vyaz'min, S.
Number of pages: 9
Pages: 463-471
Publication date: 1 Aug 2016
Peer-reviewed: Yes

Publication information

Journal: Thin Solid Films
Volume: 612
ISSN (Print): 0040-6090
Ratings: 
  • Scopus rating (2016): CiteScore 3.7 SJR 0.639 SNIP 0.863
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Materials Chemistry, Metals and Alloys, Surfaces, Coatings and Films, Surfaces and Interfaces
Keywords: Langmuir monolayer, Langmuir-Schaefer film, Polydiacetylenes with urethane group, Solid topochemical photopolymerization

Bibliographical note

EXT="Alekseev, Alexander"

Source: Scopus
Source ID: 84976884439

Research output: Contribution to journalArticleScientificpeer-review

Novel oxyfluorophosphate glasses and glass-ceramics

Effect of CaF2 addition at the expense of CaO on the thermal, physical, optical and structural properties of glasses in the NaPO3-CaO system was studied. The glasses were prepared by the conventional melt quenching method. For each glass, the thermal properties were studied by differential thermal analysis (DTA) and the optical properties by UV-Vis-NIR spectroscopy. The changes in the glass structure induced by the progressive replacement of CaO by CaF2 were investigated using IR and Raman spectroscopies. The glasses were heat treated at 20 °C above their respective glass transition temperature for 17 h to form nuclei and then at their peak crystallization temperature for 1 h to grow the nuclei into crystals. An increase in the CaF2 content increased the polymerization of the phosphate network leading to shift of the band gap to lower wavelength and reduced the crystallization tendency of the glasses. At least two crystalline phases precipitated in all the investigated glasses, the composition of which depended on the CaF2 content. Finally, bulk crystallization was suspected to occur in the oxyfluorophosphate glasses.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electronics and Communications Engineering, Research group: Biomaterials and Tissue Engineering Group, Abo Akademi University, University of Turku
Contributors: Cui, S., Massera, J., Lastusaari, M., Hupa, L., Petit, L.
Number of pages: 5
Pages: 40-44
Publication date: 1 Aug 2016
Peer-reviewed: Yes

Publication information

Journal: Journal of Non-Crystalline Solids
Volume: 445-446
ISSN (Print): 0022-3093
Ratings: 
  • Scopus rating (2016): CiteScore 3.5 SJR 0.685 SNIP 1.154
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Ceramics and Composites, Electronic, Optical and Magnetic Materials, Materials Chemistry
Keywords: Crystallization, Fluorophosphate glasses and glass-ceramics, Raman and IR spectroscopies, XRD
Source: Scopus
Source ID: 84969872500

Research output: Contribution to journalArticleScientificpeer-review

Restoring Integral Images from Focal Stacks Using Compressed Sensing Techniques

This paper contains an original development of the compressed sensing technique for restoring integral images from a number of observed 2D images. The proposed data acquisition uses a conventional camera equipped with a horizontal 1D mask placed in the pupil plane of the lens. The compressed sensing style algorithm developed is based on a sparsity hypothesis imposed on 2D cross sections of the light field.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Signal Processing, Universidad de la Laguna, University of Connecticut
Contributors: Trujillo-Sevilla, J. M., Katkovnik, V., Javidi, B., Rodríguez-Ramos, J. M.
Number of pages: 6
Pages: 701-706
Publication date: 1 Jul 2016
Peer-reviewed: Yes

Publication information

Journal: Journal of Display Technology
Volume: 12
Issue number: 7
ISSN (Print): 1551-319X
Ratings: 
  • Scopus rating (2016): CiteScore 3.6 SJR 0.672 SNIP 1.209
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Keywords: Compressed sensing, focal stack, integral imaging
Source: Scopus
Source ID: 84976358976

Research output: Contribution to journalArticleScientificpeer-review

Nonlocal soliton scattering in random potentials

We experimentally investigate the transport behaviour of nonlocal spatial optical solitons when launched in and interacting with propagation-invariant random potentials. The solitons are generated in nematic liquid crystals; the randomness is created by suitably engineered illumination of planar voltage-biased cells equipped with a photosensitive wall. We find that the fluctuations follow a super-diffusive trend, with the mean square displacement lowering for decreasing spatial correlation of the noise.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, University “Roma Tre”, CNRS, Nonlinear Optics and OptoElectronics Lab, Optics Laboratory, Department of Physics, Tampere University of Technology
Contributors: Piccardi, A., Residori, S., Assanto, G.
Number of pages: 5
Publication date: 1 Jul 2016
Peer-reviewed: Yes

Publication information

Journal: Journal of Optics
Volume: 18
Issue number: 7
Article number: 07LT01
ISSN (Print): 2040-8978
Ratings: 
  • Scopus rating (2016): CiteScore 1.63 SJR 0.715 SNIP 0.829
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials
Keywords: liquid crystals, nematicons, random potential, scattering, spatial solitons
Source: Scopus
Source ID: 84978954030

Research output: Contribution to journalArticleScientificpeer-review

The Impact of Protection Heater Delays Distribution on the Hotspot Temperature in a High-Field Accelerator Magnet

Quench protection is one of the challenges in the development of high-field superconducting magnets for future particle accelerators, such as the High-Energy and High-Luminosity LHC. The protection of the accelerator magnets up to now has relied on protection heaters to spread the normal zone across the winding, thus increasing the magnet resistance. The design of the protection heaters layout largely deals with the optimal positioning of the available heater energy on the coil surface. The aim is to quickly bring a large fraction of the winding to resistive state and induce a fast current discharge. Since the coil consists of different field regions, different approaches for heater energy distribution can be considered. Possible optimization criteria can be, for example, the minimum average delay in all the coils, the minimum first delay, or the minimum last delay. In this paper, we present a study of the impact of heater delay distribution on the resulting current decay and hotspot temperature. We use our newly developed current decay model to simulate the magnet current decay rate for different heater designs. We consider the case of the LARP-CERN MQXF magnet, being developed for the LHC luminosity upgrade.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electrical Engineering, Research area: Electromagnetics
Contributors: Salmi, T., Stenvall, A.
Publication date: 1 Jun 2016
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 26
Issue number: 4
Article number: 4001405
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2016): CiteScore 1.42 SJR 0.398 SNIP 1.132
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Condensed Matter Physics, Electronic, Optical and Magnetic Materials
Keywords: Heater delays, hotspot temperature, protection heaters, quench protection, superconductingmagnets
Source: Scopus
Source ID: 84962385287

Research output: Contribution to journalArticleScientificpeer-review

Quench Protection Study of the Updated MQXF for the LHC Luminosity Upgrade (HiLumi LHC)

In 2023, the LHC luminosity will be increased, aiming at reaching 3000 fb-1 integrated over ten years. To obtain this target, new Nb3Sn low-β quadrupoles (MQXF) have been designed for the interaction regions. These magnets present a very large aperture (150 mm, to be compared with the 70 mm of the present NbTi quadrupoles) and a very large stored energy density (120 MJ/m3). For these reasons, quench protection is one of the most challenging aspects of the design of these magnets. In fact, protection studies of a previous design showed that the simulated hot spot temperature was very close to the maximum allowed limit of 350 K; this challenge motivated improvements in the current discharge modeling, taking into account the so-called dynamic effects on the apparent magnet inductance. Moreover, quench heaters design has been studied to be going into more details. In this paper, a protection study of the updated MQXF is presented, benefitting from the experience gained by studying the previous design. A study of the voltages between turns in the magnet is also presented during both normal operation and most important failure scenarios.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electrical Engineering, Research area: Electromagnetics, Laboratorio Accelatori e Superconduttività Applicata, Fermi National Accelerator Laboratory, CERN
Contributors: Marinozzi, V., Ambrosio, G., Ferracin, P., Izquierdo Bermudez, S., Rysti, J., Salmi, T., Sorbi, M., Todesco, E.
Publication date: 1 Jun 2016
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 26
Issue number: 4
Article number: 4001805
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2016): CiteScore 1.42 SJR 0.398 SNIP 1.132
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Condensed Matter Physics, Electronic, Optical and Magnetic Materials
Keywords: Niobium compounds, quench protection, superconducting accelerators
Source: Scopus
Source ID: 84962420401

Research output: Contribution to journalArticleScientificpeer-review

Development of MQXF: The Nb3Sn Low-β Quadrupole for the HiLumi LHC

The High Luminosity (HiLumi) Large Hadron Collider (LHC) project has, as the main objective, to increase the LHC peak luminosity by a factor five and the integrated luminosity by a factor ten. This goal will be achieved mainly with a new interaction region layout, which will allow a stronger focusing of the colliding beams. The target will be to reduce the beam size in the interaction points by a factor of two, which requires doubling the aperture of the low-β (or inner triplet) quadrupole magnets. The use of Nb3Sn superconducting material and, as a result, the possibility of operating at magnetic field levels in the windings higher than 11 T will limit the increase in length of these quadrupoles, called MQXF, to acceptable levels. After the initial design phase, where the key parameters were chosen and the magnet's conceptual design finalized, the MQXF project, a joint effort between the U.S. LHC Accelerator Research Program and the Conseil Europeén pour la Recherche Nucleaíre (CERN), has now entered the construction and test phase of the short models. Concurrently, the preparation for the development of the full-length prototypes has been initiated. This paper will provide an overview of the project status, describing and reporting on the performance of the superconducting material, the lessons learnt during the fabrication of superconducting coils and support structure, and the fine tuning of the magnet design in view of the start of the prototyping phase.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electrical Engineering, Research area: Electromagnetics, European Organization for Nuclear Research, Fermi National Accelerator Laboratory, Brookhaven National Laboratory, Lawrence Berkeley National Laboratory, Istituto Nazionale Di Fisica Nucleare, Frascati
Contributors: Ferracin, P., Ambrosio, G., Anerella, M., Ballarino, A., Bajas, H., Bajko, M., Bordini, B., Bossert, R., Cheng, D. W., Dietderich, D. R., Chlachidze, G., Cooley, L., Felice, H., Ghosh, A., Hafalia, R., Holik, E., Izquierdo Bermudez, S., Fessia, P., Grosclaude, P., Guinchard, M., Juchno, M., Krave, S., Lackner, F., Marchevsky, M., Marinozzi, V., Nobrega, F., Oberli, L., Pan, H., Perez, J. C., Prin, H., Rysti, J., Rochepault, E., Sabbi, G., Salmi, T., Schmalzle, J., Sorbi, M., Sequeira Tavares, S., Todesco, E., Wanderer, P., Wang, X., Yu, M.
Publication date: 1 Jun 2016
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 26
Issue number: 4
Article number: 4000207
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2016): CiteScore 1.42 SJR 0.398 SNIP 1.132
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Condensed Matter Physics, Electronic, Optical and Magnetic Materials
Keywords: High Luminosity LHC, Interaction Regions, Low-β Quadrupoles
Source: Scopus
Source ID: 84962432718

Research output: Contribution to journalArticleScientificpeer-review

Protection Heater Design Validation for the LARP Magnets Using Thermal Imaging

Protection heaters are essential elements of a quench protection scheme for high-field accelerator magnets. Various heater designs fabricated by LARP and CERN have been already tested in the LARP high-field quadrupole HQ and presently being built into the coils of the high-field quadrupole MQXF. In order to compare the heat flow characteristics and thermal diffusion timescales of different heater designs, we powered heaters of two different geometries in ambient conditions and imaged the resulting thermal distributions using a high-sensitivity thermal video camera. We observed a peculiar spatial periodicity in the temperature distribution maps potentially linked to the structure of the underlying cable. Two-dimensional numerical simulation of heat diffusion and spatial heat distribution have been conducted, and the results of simulation and experiment have been compared. Imaging revealed hot spots due to a current concentration around high curvature points of heater strip of varying cross sections and visualized thermal effects of various interlayer structural defects. Thermal imaging can become a future quality control tool for the MQXF coil heaters.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electrical Engineering, Lawrence Berkeley National Laboratory, Fermi National Accelerator Laboratory, European Center for Nuclear Physics
Contributors: Marchevsky, M., Turqueti, M., Cheng, D. W., Felice, H., Sabbi, G., Salmi, T., Stenvall, A., Chlachidze, G., Ambrosio, G., Ferracin, P., Izquierdo Bermudez, S., Perez, J. C., Todesco, E.
Publication date: 1 Jun 2016
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 26
Issue number: 4
Article number: 4003605
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2016): CiteScore 1.42 SJR 0.398 SNIP 1.132
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Condensed Matter Physics, Electronic, Optical and Magnetic Materials
Keywords: Quench Protection, Superconducting Magnets, Thermal Imaging
Source: Scopus
Source ID: 84964335731

Research output: Contribution to journalArticleScientificpeer-review

Roadmap on optical rogue waves and extreme events

The pioneering paper 'Optical rogue waves' by Solli et al (2007 Nature 450 1054) started the new subfield in optics. This work launched a great deal of activity on this novel subject. As a result, the initial concept has expanded and has been enriched by new ideas. Various approaches have been suggested since then. A fresh look at the older results and new discoveries has been undertaken, stimulated by the concept of 'optical rogue waves'. Presently, there may not by a unique view on how this new scientific term should be used and developed. There is nothing surprising when the opinion of the experts diverge in any new field of research. After all, rogue waves may appear for a multiplicity of reasons and not necessarily only in optical fibers and not only in the process of supercontinuum generation. We know by now that rogue waves may be generated by lasers, appear in wide aperture cavities, in plasmas and in a variety of other optical systems. Theorists, in turn, have suggested many other situations when rogue waves may be observed. The strict definition of a rogue wave is still an open question. For example, it has been suggested that it is defined as 'an optical pulse whose amplitude or intensity is much higher than that of the surrounding pulses'. This definition (as suggested by a peer reviewer) is clear at the intuitive level and can be easily extended to the case of spatial beams although additional clarifications are still needed. An extended definition has been presented earlier by N Akhmediev and E Pelinovsky (2010 Eur. Phys. J. Spec. Top. 185 1-4). Discussions along these lines are always useful and all new approaches stimulate research and encourage discoveries of new phenomena. Despite the potentially existing disagreements, the scientific terms 'optical rogue waves' and 'extreme events' do exist. Therefore coordination of our efforts in either unifying the concept or in introducing alternative definitions must be continued. From this point of view, a number of the scientists who work in this area of research have come together to present their research in a single review article that will greatly benefit all interested parties of this research direction. Whether the authors of this 'roadmap' have similar views or different from the original concept, the potential reader of the review will enrich their knowledge by encountering most of the existing views on the subject. Previously, a special issue on optical rogue waves (2013 J. Opt. 15 060201) was successful in achieving this goal but over two years have passed and more material has been published in this quickly emerging subject. Thus, it is time for a roadmap that may stimulate and encourage further research.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Australian National University, Université de Bourgogne Franche-Comté, Universita degli Studi di Brescia, Texas A and M University at Qatar, Shunde Polytechnic, Xi'an Jiaotong University, CSIC - Instituto de &amp;Oacute;ptica Daza de Vald&amp;eacute;s (IO), CRPP, Universidad Adolfo Ibánez, Université libre de Bruxelles (ULB), Vrije Universiteit Brussel, Université Lille 1, Université de Franche-Comté, Leibniz-Universität Hannover, Weierstrass-Institut für Angewandte Analysis und Stochastik, Max Born Institute, Universitat Politécnica de Catalunya, The University of Auckland, Dodd-Walls Centre for Photonic and Quantum Technologies, CNRS, CNR-INO
Contributors: Akhmediev, N., Kibler, B., Baronio, F., Belić, M., Zhong, W. P., Zhang, Y., Chang, W., Soto-Crespo, J. M., Vouzas, P., Grelu, P., Lecaplain, C., Hammani, K., Rica, S., Picozzi, A., Tlidi, M., Panajotov, K., Mussot, A., Bendahmane, A., Szriftgiser, P., Genty, G., Dudley, J., Kudlinski, A., Demircan, A., Morgner, U., Amiraranashvili, S., Bree, C., Steinmeyer, G., Masoller, C., Broderick, N. G. R., Runge, A. F. J., Erkintalo, M., Residori, S., Bortolozzo, U., Arecchi, F. T., Wabnitz, S., Tiofack, C. G., Coulibaly, S., Taki, M.
Publication date: 1 Jun 2016
Peer-reviewed: Yes

Publication information

Journal: Journal of Optics
Volume: 18
Issue number: 6
Article number: 063001
ISSN (Print): 2040-8978
Ratings: 
  • Scopus rating (2016): CiteScore 1.63 SJR 0.715 SNIP 0.829
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials
Keywords: extreme events, nonlinear optics, rogue waves

Bibliographical note

EXT="Steinmeyer, Günter"
EXT="Erkintalo, Miro"

Source: Scopus
Source ID: 84975818584

Research output: Contribution to journalArticleScientificpeer-review

Effect of incorporation of CdS NPs on performance of PTB7: PCBM organic solar cells

It has been well known that incorporation of nano-heterostructures of various metals, semiconductors and dielectric materials in the active layer of organic solar cells (OSCs) helps in improving power conversion efficiency (PCE). In the present study, we demonstrated microwave synthesis of CdS nanoparticles (NPs) for their application in one of most efficient OSCs consisting of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]] (PTB7): [6,6]-phenyl C71-butyric acid methyl ester (PCBM) photoactive blend. This is crucial to fully explore the promising features of low cost and scalability in organic-inorganic hybrid solar cells. Synthesized CdS NPs are slightly elongated and highly crystalline with their absorption lies in the visible region as confirmed by High resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), UV-Vis absorption spectroscopy studies. Our experimental results for the devices in an inverted geometry having a structure ITO/ZnO/PTB7: CdS: PCBM/MoO3/Ag has shown increase in Jsc and PCE by nearly 10%. However, it was observed that this increase is only when NPs were added in the low concentration in active layer. UV-Vis absorption spectroscopy, Photoluminescence (PL) and atomic force microscopy (AFM) studies were carried out in order understand the device performance.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Electronics and Communications Engineering, Indian Institute of Technology Bombay, Organic and Nano-electronics Group
Contributors: Sharma, R., Bhalerao, S., Gupta, D.
Number of pages: 7
Pages: 274-280
Publication date: 1 Jun 2016
Peer-reviewed: Yes

Publication information

Journal: Organic Electronics: physics, materials, applications
Volume: 33
ISSN (Print): 1566-1199
Ratings: 
  • Scopus rating (2016): CiteScore 6.3 SJR 1.081 SNIP 0.944
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Biomaterials, Chemistry(all), Condensed Matter Physics, Materials Chemistry, Electrical and Electronic Engineering
Keywords: CdS nanoparticles, Microwave synthesis, Organic solar cells, PCBM, PL quenching, PTB7
Source: Scopus
Source ID: 84962355464

Research output: Contribution to journalArticleScientificpeer-review

Test Results of the LARP Nb3Sn Quadrupole HQ03a

The U.S. LHC Accelerator Research Program (LARP) has been developing Nb3Sn quadrupoles of increasing performance for the high-luminosity upgrade of the large hadron collider. The 120-mm aperture high-field quadrupole (HQ) models are the last step in the RD phase supporting the development of the new IR Quadrupoles (MQXF). Three series of HQ coils were fabricated and assembled in a shell-based support structure, progressively optimizing the design and fabrication process. The final set of coils consistently applied the optimized design solutions and was assembled in the HQ03a model. This paper reports a summary of the HQ03a test results, including training, mechanical performance, field quality, and quench studies.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Fermi National Accelerator Laboratory, Brookhaven National Laboratory, European Organization for Nuclear Research, Lawrence Berkeley National Laboratory
Contributors: DiMarco, J., Ambrosio, G., Anerella, M., Bajas, H., Chlachidze, G., Borgnolutti, F., Bossert, R., Cheng, D., Dietderich, D., Felice, H., Holik, T., Pan, H., Ferracin, P., Ghosh, A., Godeke, A., Hafalia, A. R., Marchevsky, M., Orris, D., Ravaioli, E., Sabbi, G., Salmi, T., Schmalzle, J., Stoynev, S., Strauss, T., Sylvester, C., Tartaglia, M., Todesco, E., Wanderer, P., Wang, X., Yu, M.
Publication date: 1 Jun 2016
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 26
Issue number: 4
Article number: 4005105
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2016): CiteScore 1.42 SJR 0.398 SNIP 1.132
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: High field accelerator magnets, NbSn
Source: Scopus
Source ID: 84971631243

Research output: Contribution to journalArticleScientificpeer-review

Tuning electronic properties of graphene heterostructures by amorphous-to-crystalline phase transitions

The remarkable ability of phase change materials (PCM) to switch between amorphous and crystalline states on a nanosecond time scale could provide new opportunities for graphene engineering. We have used density functional calculations to investigate the structures and electronic properties of heterostructures of thin amorphous and crystalline films of the PCM GeTe (16 Å thick) and Ge2Sb2Te5 (20 Å) between graphene layers. The interaction between graphene and PCM is very weak, charge transfer is negligible, and the structures of the chalcogenide films differ little from those of bulk phases. A crystalline GeTe (111) layer induces a band gap opening of 80 meV at the Dirac point. This effect is absent for the amorphous film, but the Fermi energy shifts down along the Dirac cone by -60 meV. Ge2Sb2Te5 shows similar features, although inherent disorder in the crystalline rocksalt structure reduces the contrast in band structure from that in the amorphous structure. These features originate in charge polarization within the crystalline films, which show electromechanical response (piezoelectricity) upon compression, and show that the electronic properties of graphene structures can be tuned by inducing ultrafast structural transitions within the chalcogenide layers. Graphene can also be used to manipulate the structural state of the PCM layer and its electronic and optical properties.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Research area: Computational Physics, Research group: Materials and Molecular Modeling, COMP Centre of Excellence, Aalto University, Molecular Foundry, Lawrence Berkeley National Laboratory, Forschungszentrum Jülich (FZJ)
Contributors: Kulju, S., Akola, J., Prendergast, D., Jones, R. O.
Number of pages: 8
Publication date: 31 May 2016
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 93
Issue number: 19
Article number: 195443
ISSN (Print): 1098-0121
Ratings: 
  • Scopus rating (2016): CiteScore 3.16 SJR 2.339 SNIP 1.183
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Electronic, Optical and Magnetic Materials
Source: Scopus
Source ID: 84973352747

Research output: Contribution to journalArticleScientificpeer-review

Influence of As/group-III flux ratio on defects formation and photovoltaic performance of GaInNAs solar cells

The correlation between the As to group III flux ratio and photovoltaic performance of GaIn0.1N0.03As solar cells fabricated by molecular beam epitaxy is systematically investigated. The results show that flux ratio has a remarkable influence on the formation of defect traps. Furthermore, the formation of defects at different flux ratios is correlating with the variation of the background doping level and the photovoltaic performance. In particular, this study reveals a linear dependency between current generation, dark saturation current, defect densities, photoluminescence peak intensity and the flux ratio. A significant increase in solar cell performance, exhibiting maximum external quantum efficiency of 90%, is obtained when As/group-III ratio is decreased close to the stoichiometric limit. For optimized growth condition, the 1 eV GaIn0.1N0.03As solar cell exhibits a short circuit current density as high as 17.9 mA/cm2 calculated from the external quantum efficiency data (AM0 conditions) with 870 nm high-pass filter. This value reflects the potential of the GaInNAs cell for current matching and power generation in high efficiency solar cells incorporating three- or four- junctions.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Optoelectronics Research Centre, Research group: Semiconductor Technology and Applications
Contributors: Polojärvi, V., Aho, A., Tukiainen, A., Raappana, M., Aho, T., Schramm, A., Guina, M.
Number of pages: 8
Pages: 213-220
Publication date: 1 May 2016
Peer-reviewed: Yes

Publication information

Journal: Solar Energy Materials and Solar Cells
Volume: 149
ISSN (Print): 0927-0248
Ratings: 
  • Scopus rating (2016): CiteScore 4.97 SJR 1.599 SNIP 1.697
Original language: English
ASJC Scopus subject areas: Renewable Energy, Sustainability and the Environment, Electronic, Optical and Magnetic Materials, Surfaces, Coatings and Films
Keywords: Defects, Dilute nitrides, III-V semiconductors, Material characterization, Molecular beam epitaxy, Multijunction solar cells
Source: Scopus
Source ID: 84957536411

Research output: Contribution to journalArticleScientificpeer-review

Vortex stabilization by means of spatial solitons in nonlocal media

We investigate how optical vortices, which tend to be azimuthally unstable in local nonlinear materials, can be stabilized by a copropagating coaxial spatial solitary wave in nonlocal, nonlinear media. We focus on the formation of nonlinear vortex-soliton vector beams in reorientational soft matter, namely nematic liquid crystals, and report on experimental results, as well as numerical simulations.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics
Contributors: Izdebskaya, Y., Krolikowski, W., Smyth, N. F., Assanto, G.
Publication date: 1 May 2016
Peer-reviewed: Yes

Publication information

Journal: Journal of Optics
Volume: 18
Issue number: 5
Article number: 054006
ISSN (Print): 2040-8978
Ratings: 
  • Scopus rating (2016): CiteScore 1.63 SJR 0.715 SNIP 0.829
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials
Keywords: liquid crystals, optical vortex, self-action effects, spatial solitons
Source: Scopus
Source ID: 84969245814

Research output: Contribution to journalArticleScientificpeer-review

Effect of Hole Transporting Material on Charge Transfer Processes in Zinc Phthalocyanine Sensitized ZnO Nanorods

The photoinduced electron transfer processes were studied for hybrid systems consisting of self-assembled monolayer of zinc phthalocyanine (ZnPc) assembled on ZnO nanorods and a film of organic hole transporting material (HTM) atop. Polythiophene (P3HT) or Spiro-OMeTAD were used as HTM. The study was carried out by ultrafast transient absorption spectroscopy technique with selective excitation of ZnPc at 680 nm or P3HT at 500 nm. Data analysis revealed that photoexcitation of ZnPc in the structure ZnO|ZnPc|P3HT results in a fast (1.8 ps) electron transfer from ZnPc to ZnO, which is followed by a hole transfer from the ZnPc cation to P3HT roughly in 30 ps. However, in the case of ZnO|ZnPc|Spiro-OMeTAD structure, the primary reaction upon excitation of ZnPc is a fast (0.5 ps) hole transfer from ZnPc to Spiro-OMeTAD, and the second step is electron injection from the ZnPc anion to ZnO in roughly 120 ps. Thus, we demonstrate two structurally very similar hybrid architectures that implement two different mechanisms for photoinduced charge separation found in dye-sensitized or in organic solar cells.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Chemistry and Bioengineering, Research group: Supramolecular photochemistry
Contributors: Hakola, H., Sariola-Leikas, E., Efimov, A., Tkachenko, N. V.
Number of pages: 8
Pages: 7044-7051
Publication date: 21 Apr 2016
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry C
Volume: 120
Issue number: 13
ISSN (Print): 1932-7447
Ratings: 
  • Scopus rating (2016): CiteScore 7.9 SJR 1.964 SNIP 1.189
Original language: English
ASJC Scopus subject areas: Physical and Theoretical Chemistry, Electronic, Optical and Magnetic Materials, Surfaces, Coatings and Films, Energy(all)
Source: Scopus
Source ID: 84964529902

Research output: Contribution to journalArticleScientificpeer-review

Thermal, structural and optical properties of Er3+ doped phosphate glasses containing silver nanoparticles

The melt-quenching method is employed to prepare the amorphous phosphate glasses containing silver nanoparticles (Ag NPs). The structural characteristics of phosphate glasses were investigated by X-ray diffraction, thermal analysis, transmission electron microscopy, UV-Vis spectroscopy, Raman, and infrared spectroscopy. The transmission electron microscopic images confirm the presence of spherical silver NPs having an average diameter in the range of 20-40 nm. The EDX analysis spectrum shows the presence of Ag element. Important structural changes induced by the Ag2CO3 addition to the phosphate glass, Raman- and IR-spectroscopic studies were carried out in order to correlate the variations in the glass properties with variations of the glass structure. The surface plasmon resonance (SPR) peak of silver nanoparticles embedded in Er3 + doped phosphate glass is evidenced at ∼403 nm. From the absorption spectra, the optical band gap is found to decrease with the increase of Ag NPs' concentration. All the obtained results in the present study were reported and discussed in detail.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electronics and Communications Engineering, Research group: Biomaterials and Tissue Engineering Group, Physical Chemistry Laboratory of Mineral Materials and Their Applications, National Center of Research in Materials Science, Åbo Akademi
Contributors: Soltani, I., Hraiech, S., Horchani-Naifer, K., Massera, J., Petit, L., Férid, M.
Number of pages: 7
Pages: 67-73
Publication date: 15 Apr 2016
Peer-reviewed: Yes

Publication information

Journal: Journal of Non-Crystalline Solids
Volume: 438
ISSN (Print): 0022-3093
Ratings: 
  • Scopus rating (2016): CiteScore 3.5 SJR 0.685 SNIP 1.154
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Ceramics and Composites, Electronic, Optical and Magnetic Materials, Materials Chemistry
Keywords: FTIR and Raman spectra, Phosphate glasses, Silver nanoparticles (Ag NPs), Thermal stability

Bibliographical note

EXT="Petit, L."

Source: Scopus
Source ID: 84960866255

Research output: Contribution to journalArticleScientificpeer-review

Wetting hysteresis induced by temperature changes: Supercooled water on hydrophobic surfaces

The state and stability of supercooled water on (super)hydrophobic surfaces is crucial for low temperature applications and it will affect anti-icing and de-icing properties. Surface characteristics such as topography and chemistry are expected to affect wetting hysteresis during temperature cycling experiments, and also the freezing delay of supercooled water. We utilized stochastically rough wood surfaces that were further modified to render them hydrophobic or superhydrophobic. Liquid flame spraying (LFS) was utilized to create a multi-scale roughness by depositing titanium dioxide nanoparticles. The coating was subsequently made non-polar by applying a thin plasma polymer layer. As flat reference samples modified silica surfaces with similar chemistries were utilized. With these substrates we test the hypothesis that superhydrophobic surfaces also should retard ice formation. Wetting hysteresis was evaluated using contact angle measurements during a freeze-thaw cycle from room temperature to freezing occurrence at -7 °C, and then back to room temperature. Further, the delay in freezing of supercooled water droplets was studied at temperatures of -4 °C and -7 °C. The hysteresis in contact angle observed during a cooling-heating cycle is found to be small on flat hydrophobic surfaces. However, significant changes in contact angles during a cooling-heating cycle are observed on the rough surfaces, with a higher contact angle observed on cooling compared to during the subsequent heating. Condensation and subsequent frost formation at sub-zero temperatures induce the hysteresis. The freezing delay data show that the flat surface is more efficient in enhancing the freezing delay than the rougher surfaces, which can be rationalized considering heterogeneous nucleation theory. Thus, our data suggests that molecular flat surfaces, rather than rough superhydrophobic surfaces, are beneficial for retarding ice formation under conditions that allow condensation and frost formation to occur.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Research area: Aerosol Physics, Research group: Aerosol Synthesis, KTH Royal Institute of Technology, Surface and Corrosion Science, SP Technical Research Institute of Sweden, Department of Civil and Architectural Engineering, Nanostructure Physics
Contributors: Heydari, G., Sedighi Moghaddam, M., Tuominen, M., Fielden, M., Haapanen, J., Mäkelä, J. M., Claesson, P. M.
Number of pages: 13
Pages: 21-33
Publication date: 15 Apr 2016
Peer-reviewed: Yes

Publication information

Journal: Journal of Colloid and Interface Science
Volume: 468
ISSN (Print): 0021-9797
Ratings: 
  • Scopus rating (2016): CiteScore 7.2 SJR 1.156 SNIP 1.277
Original language: English
ASJC Scopus subject areas: Surfaces, Coatings and Films, Electronic, Optical and Magnetic Materials, Biomaterials, Colloid and Surface Chemistry
Keywords: Contact angle, Hydrophobization, Liquid flame spray (LFS), Morphology, Multi-scale roughness, Plasma polymerization, Supercooled water, Superhydrophobicity, Wetting hysteresis, Wood
Source: Scopus
Source ID: 84955276633

Research output: Contribution to journalArticleScientificpeer-review

3-D Numerical Modeling of AC Losses in Multifilamentary MgB2 Wires

Due to their high current carrying capacity, round geometry and low cost, MgB2 wires are promising candidates for realizing high power cables. However, their operating temperature comprised between 4.2 K and 25 K makes AC losses a critical issue for those cables. In order to optimize the cable architecture for minimizing AC losses, one must be able to predict them quite accurately. As a first step in this direction, we addressed the numerical computation of a single multi-filamentary MgB2 wire that forms the basic element of a high current cable. The wire under consideration has 36 twisted MgB2 filaments disposed on three concentric layers and embedded in a pure nickel matrix. An initial comparison between 2-D and 3-D finite elements was performed in order to justify the need of a full 3-D model, without which coupling losses in the matrix cannot be modeled properly. This is of prime importance since coupling loss is the dominant loss mechanism at high applied fields. Then, simulations of simpler geometries (6- and 18- filament wires) submitted to various transport currents and/or applied fields were performed to identify trends in AC losses and find the best numerical tools for scaling up simulations to the full 36-filament case. The complexity of the model was increased progressively, starting with MgB2 filaments in air matrix, then adding electrical conductivity and magnetic properties in the nickel matrix.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research area: Electromagnetics, Department of Electrical Engineering, G2Elab/Institut Néel, Polytechnique Montréal, Cedrat S.A. 15 Chemin de Malacher-Inovallé, Nexans France
Contributors: Escamez, G., Sirois, F., Lahtinen, V., Stenvall, A., Badel, A., Tixador, P., Ramdane, B., Meunier, G., Perrin-Bit, R., Bruzek, C. É.
Publication date: 1 Apr 2016
Peer-reviewed: Yes
Early online date: 2016

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 26
Issue number: 3
Article number: 4701907
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2016): CiteScore 1.42 SJR 0.398 SNIP 1.132
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Condensed Matter Physics, Electronic, Optical and Magnetic Materials
Keywords: AC losses, FEM modelling, MgB2, power cable
Source: Scopus
Source ID: 84963878465

Research output: Contribution to journalArticleScientificpeer-review

Status of the Demonstrator Magnets for the EuCARD-2 Future Magnets Project

EuCARD-2 is a project partly supported by FP7 European Commission aiming at exploring accelerator magnet technology for 20-T dipole operating field. The EuCARD-2 collaboration is liaising with similar programs for high-field magnets in the U.S. and Japan. EuCARD-2 focuses, through the work package 10 'future magnets,' on the development of a 10-kA-class superconducting high-current-density cable suitable for accelerator magnets, for a 5-T stand-alone dipole of 40-mm bore and about 1-m length. After stand-alone testing, the magnet will be inserted in a large bore background dipole, 10-18 T. This paper reports on the design and development of models, which are called Feather0, wound with REBCO Roebel cable. Based on aligned block design to take advantage of the anisotropy of the REBCO tapes, Feather0 is a precursor of Feather2, which should reach the project goals in 2016. Feather0 is planned to be tested both in stand alone and as an insert mounted in the CERN Fresca facility providing 10-T background field. The progress of other designs pursued in the collaboration, one based on classical cos θ layout with Roebel cable and the other based on coil block with stacked tape cable, will be also reported.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electrical Engineering, Research area: Electromagnetics, European Organization for Nuclear Research, Grenoble Institute of Technology, University of Twente, French Atomic Energy Commission (CEA) Saclay, Karlsruhe Institute of Technology, Insitute for Technical Physics, Germany, Universite de Geneve, Bruker HTS, Istituto Nazionale Di Fisica Nucleare, Frascati, University of Southampton, United Kingdom, Danish Institute of Technology
Contributors: Kirby, G., Rossi, L., Badel, A., Bajko, M., Ballarino, A., Bottura, L., Dhalle, M., Durante, M., Fazilleau, P., Fleiter, J., Goldacker, W., Härö, E., Himbele, J., Kario, A., Langeslag, S., Lorin, C., Murtzomaki, J., Van Nugteren, J., De Rijk, G., Salmi, T., Senatore, C., Stenvall, A., Tixador, P., Usoskin, A., Volpini, G., Yang, Y., Zangenberg, N.
Publication date: 1 Apr 2016
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 26
Issue number: 3
Article number: 4003307
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2016): CiteScore 1.42 SJR 0.398 SNIP 1.132
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Condensed Matter Physics, Electronic, Optical and Magnetic Materials
Keywords: Accelerators magnets, CLIQ, EuCARD-2, future magnets, higherature-superconductors, superconducting magnets
Source: Scopus
Source ID: 84963812427

Research output: Contribution to journalArticleScientificpeer-review

Structural and Electrical Characterization of Solution-Processed Electrodes for Piezoelectric Polymer Film Sensors

Solution-processable graphene and carbon nanotube-based electrode materials were used here to provide electrodes on flexible piezoelectric polyvinylidenefluoride sensors. Piezoelectric sensitivity measurements, image-based analysis, adhesion tests, and sheet resistance measurements
were applied to these printable sensors to rigorously analyze their performance and structure. The printable sensors showed electrical performance similar to metallized sensors, whereas the adhesion of the solution-processed materials to the substrate is not as high as that of the evaporated metal films. This also
affects the measured sensor sensitivity values. The measurements based on optical images were found to be a promising method to capture detailed information about the electrode surface structure.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Automation Science and Engineering, Research area: Microsystems, Research area: Measurement Technology and Process Control
Contributors: Rajala, S., Mettänen, M., Tuukkanen, S.
Number of pages: 8
Pages: 1692-1699
Publication date: 15 Mar 2016
Peer-reviewed: Yes

Publication information

Journal: IEEE Sensors Journal
Volume: 16
Issue number: 6
ISSN (Print): 1530-437X
Ratings: 
  • Scopus rating (2016): CiteScore 3.12 SJR 0.654 SNIP 1.697
Original language: English
ASJC Scopus subject areas: Biomedical Engineering, Electronic, Optical and Magnetic Materials, Surfaces and Interfaces
Keywords: Printed electrodes, image analysis, measurement, piezoelectric films, piezoelectric transducers, SHEAR-STRESS MEASUREMENTS, GRAPHENE, PVDF
Source: Bibtex
Source ID: urn:baf47c637d585669f900addd29c0f9bc

Research output: Contribution to journalArticleScientificpeer-review

Evaluation of Aerosol, Superfine Inkjet, and Photolithography Printing Techniques for Metallization of Application Specific Printed Electronic Circuits

Application specific printed electronic circuits (ASPECs) are the corresponding term with application-specified ICs for printed electronics. The same as any new technology, printed electronics is suffering from some restrictions in design and process technology aspects. An important stage in the ASPEC design is the final wiring of the organic thin-film transistor arrays or gate arrays to customize it to implement any specific target application that fits in their structure. In this paper, we evaluate two additive manufacturing technologies: aerosol jet using Optomec M3D and electrohydrodynamic printer using superfine inkjet. Both techniques are based on direct-writing of the pattern corresponding to any individual circuit being fabricated (digital printing) enabled by the mask-free noncontact deposition of materials. Finally, these structures will be compared with the corresponding photolithography mask technology. Some parameterized test vehicles, with different instantiations for the variation of line widths and separations, have been designed to be wired using the target technologies. These test vehicles have been fabricated at the Centre for Process Innovation by a five masks lithography and subtractive patterning technology. Results show that both direct printing technologies are feasible for the fabrication of the gate-array customization, thus allowing individual personalization of every circuit what can produce added value functionalities at low cost such as the equivalent effect of having an ROM memory which final contents could be customized at home by using low-cost digital printing technologies. Further interactions between transistor bulk and wiring technologies can improve the obtained performance in order to end up in an industrialized process.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electronics and Communications Engineering, Research group: Laboratory for Future Electronics, Universitat Autònoma de Barcelona, Centre for Process Innovation Limited, NeuDrive Ltd., National Research Council, University Autonoma of Barcelona
Contributors: Mashayekhi, M., Winchester, L., Evans, L., Pease, T., Laurila, M., Mäntysalo, M., Ogier, S., Teres, L., Carrabina, J.
Number of pages: 8
Pages: 1246-1253
Publication date: 1 Mar 2016
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Electron Devices
Volume: 63
Issue number: 3
ISSN (Print): 0018-9383
Ratings: 
  • Scopus rating (2016): CiteScore 5.2 SJR 1.009 SNIP 1.668
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Keywords: Additive manufacturing, aerosol jet (AJ), application specific printed electronic circuits (ASPECs), application-specified IC (ASIC), gate array, photolithography, printed electronics, superfine inkjet (SIJ)
Source: Scopus
Source ID: 84969344785

Research output: Contribution to journalArticleScientificpeer-review

Piezoresistive natural rubber-multiwall carbon nanotube nanocomposite for sensor applications

We explore, both experimentally and theoretically, the possibility to use a composite of natural rubber (NR) and multiwall carbon nanotubes (MWCNT) as a piezoresistive tensile sensor. As an essentially new feature relative to the previous work, we have performed a systematic study of the mechanism of the piezoresistance at large deformations in a wide range of MWCNT concentrations and crosslinking degrees of the host rubber material. In qualitative agreement with the previous work, the conductivity of the unstrained NR/MWCNT nanocomposite is shown to be adequately described by the percolation theory with the critical exponent evaluated to ∼2.31. Varying tensile stress-induced strains in the composite has been shown to results in a non-linear electrical response that cannot be described by simple modifications of the percolation theory. In order to explain the observed non-linear dependence of the resistance R of the composite on the strain ε, we have developed a scaling theory that relates this resistance to the structural changes in the conducting MWCNT network caused by deforming the host NR. Based on the obtained results, we discuss the ways of using the highly stretchable conductive elastomer composites as an efficient piezoresistive tensile sensor.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Materials Science, Rubber Technology Centre, Indian Institute of Technology Kharagpur, Vodafone Department of Mobile Communications Systems, University of Münster, Leibniz-Institut für Polymerforschung Dresden E.V.
Contributors: Selvan, N. T., Eshwaran, S. B., Das, A., Stöckelhuber, K. W., Wießner, S., Pötschke, P., Nando, G. B., Chervanyov, A. I., Heinrich, G.
Number of pages: 12
Pages: 102-113
Publication date: 1 Mar 2016
Peer-reviewed: Yes

Publication information

Journal: Sensors and Actuators, A: Physical
Volume: 239
ISSN (Print): 0924-4247
Ratings: 
  • Scopus rating (2016): CiteScore 4.8 SJR 0.787 SNIP 1.619
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Instrumentation, Condensed Matter Physics, Surfaces, Coatings and Films, Metals and Alloys, Electrical and Electronic Engineering
Keywords: Sensor rubber filler strain nano-composite conductivity
Source: Scopus
Source ID: 84955467512

Research output: Contribution to journalArticleScientificpeer-review

Ambient-Pressure XPS Study of a Ni-Fe Electrocatalyst for the Oxygen Evolution Reaction

Chemical analysis of solid-liquid interfaces under electrochemical conditions has recently become feasible due to the development of new synchrotron radiation techniques. Here we report the use of "tender" X-ray ambient-pressure X-ray photoelectron spectroscopy (APXPS) to characterize a thin film of Ni-Fe oxyhydroxide electrodeposited on Au as the working electrode at different applied potentials in 0.1 M KOH as the electrolyte. Our results show that the as-prepared 7 nm thick Ni-Fe (50% Fe) film contains Fe and Ni in both their metallic as well as oxidized states, and undergoes further oxidation when the sample is subjected to electrochemical oxidation-reduction cycles. Metallic Fe is oxidized to Fe3+ and metallic Ni to Ni2+/3+. This work shows that it is possible to monitor the chemical nature of the Ni-Fe catalyst as a function of potential when the corresponding current densities are small. This allows for operando measurements just above the onset of OER; however, current densities as they are desired in photoelectrochemical devices (∼1-10 mA cm-2) could not be achieved in this work, due to ohmic losses in the thin electrolyte film. We use a two-dimensional model to describe the spatial distribution of the electrochemical potential, current density, and pH as a function of the position above the electrolyte meniscus, to provide guidance toward enabling the acquisition of operando APXPS at high current density. The shifts in binding energy of water with applied potential predicted by the model are in good agreement with the experimental values.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Optoelectronics Research Centre, Research group: Surface Science, SUNCAT Center for Interface Science and Catalysis, SLAC National Accelerator Laboratory, Department of Chemical and Biomolecular Engineering, Berkeley, Materials Sciences Division, Lawrence Berkeley National Laboratory, Materials and Corrosion Engineering, Exponent, Inc., Polymer Science and Materials Chemistry
Contributors: Ali-Löytty, H., Louie, M. W., Singh, M. R., Li, L., Sanchez Casalongue, H. G., Ogasawara, H., Crumlin, E. J., Liu, Z., Bell, A. T., Nilsson, A., Friebel, D.
Number of pages: 7
Pages: 2247-2253
Publication date: 4 Feb 2016
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry C
Volume: 120
Issue number: 4
ISSN (Print): 1932-7447
Ratings: 
  • Scopus rating (2016): CiteScore 7.9 SJR 1.964 SNIP 1.189
Original language: English
ASJC Scopus subject areas: Physical and Theoretical Chemistry, Electronic, Optical and Magnetic Materials, Surfaces, Coatings and Films, Energy(all)
Electronic versions: 
URLs: 
Source: Scopus
Source ID: 84957588014

Research output: Contribution to journalArticleScientificpeer-review

Effects of insertion of strain-engineering Ga(In)NAs layers on optical properties of InAs/GaAs quantum dots for high-efficiency solar cells

We report study on stacked InAs/GaNAs quantum dots heterostructures with dilute nitride GaInNAs strain mediating layers embedded in GaAs p-i-n solar cell structure. The insertion of GaInNAs strain mediating layers in the vicinity of the strain compensated InAs/GaNAs quantum dots heterostructures enhances their surface density, improves and significantly red shifts their light emission. Embedding a stack of the strain-mediated InAs/GaInNAs/GaNAs quantum dots in the i region of a GaAs p-i-n solar cell leads also to a red shift of the absorption edge of the solar cells and improves the solar cell photogenerated currents at longer wavelengths beyond 1200 nm.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Optoelectronics Research Centre, Research group: Semiconductor Technology and Applications, National Institute for Research and Development in Microtechnologies Romania, Faculty of Exact Sciences and Engineering, Hyperion University
Contributors: Pavelescu, E., Polojärvi, V., Schramm, A., Tukiainen, A., Aho, A., Zhang, W., Puustinen, J., Salmi, J., Guina, M.
Number of pages: 4
Pages: 177-180
Publication date: 1 Feb 2016
Peer-reviewed: Yes

Publication information

Journal: Optical Materials
Volume: 52
ISSN (Print): 0925-3467
Ratings: 
  • Scopus rating (2016): CiteScore 3.8 SJR 0.636 SNIP 1.061
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics, Computer Science(all)
Keywords: Dilute nitrides, Molecular beam epitaxy, Optical properties

Bibliographical note

EXT="Pavelescu, Emil-Mihai"

Source: Scopus
Source ID: 84959293536

Research output: Contribution to journalArticleScientificpeer-review

Ghost imaging in the time domain

Ghost imaging is a novel technique that produces the image of an object by correlating the intensity of two light beams, neither of which independently carries information about the shape of the object. Ghost imaging has opened up new perspectives to obtain highly resolved images, even in the presence of noise and turbulence. Here, by exploiting the duality between light propagation in space and time, we demonstrate the temporal analogue of ghost imaging. We use a conventional fast detector that does not see the temporal ‘object’ to be characterized and a slow integrating ‘bucket’ detector that does see the object but without resolving its temporal structure. Our experiments achieve temporal resolution at the picosecond level and are insensitive to the temporal distortion that may occur after the object. The approach is scalable, can be integrated on-chip, and offers great promise for dynamic imaging of ultrafast waveforms.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Research area: Optics, Research group: Nonlinear Fiber Optics
Contributors: Ryczkowski, P., Barbier, M., Friberg, A. T., Dudley, J. M., Genty, G.
Number of pages: 4
Pages: 167-170
Publication date: 1 Feb 2016
Peer-reviewed: Yes

Publication information

Journal: Nature Photonics
Issue number: 10
ISSN (Print): 1749-4885
Ratings: 
  • Scopus rating (2016): CiteScore 61 SJR 15.689 SNIP 9.052
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Source: Scopus
Source ID: 84957042861

Research output: Contribution to journalArticleScientificpeer-review

Effect of the glass melting condition on the processing of phosphate-based glass-ceramics with persistent luminescence properties

In this paper, we discuss the impact of the temperature and the duration of the melting on the persistent luminescence properties of phosphate glasses within the P2O5-Na2O-CaO and P2O5-Na2O-SrO systems prepared using a standard melting process in normal atmosphere by adding Sr4Al14O25:Eu2+,Dy3+ microparticles in the glass batch before melting. Glasses with persistent luminescence properties can be successfully prepared if the melting conditions are carefully controlled.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electronics and Communications Engineering, Research group: Biomaterials and Tissue Engineering Group, Abo Akad Univ, Abo Akademi University, Dept Phys, Academy of Sciences, Turun Yliopisto/Turun Biomateriaalikeskus, University of Turku, University of São Paulo
Contributors: Massera, J., Gaussiran, M., Głuchowski, P., Lastusaari, M., Petit, L., Hölsä, J., Hupa, L.
Number of pages: 6
Pages: 56-61
Publication date: 1 Feb 2016
Peer-reviewed: Yes

Publication information

Journal: Optical Materials
Volume: 52
ISSN (Print): 0925-3467
Ratings: 
  • Scopus rating (2016): CiteScore 3.8 SJR 0.636 SNIP 1.061
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics, Computer Science(all)
Keywords: Energy dispersive analysis of X-rays (EDS or EDAX), Glasses, Heat treatment, Luminescence
Source: Scopus
Source ID: 84959313726

Research output: Contribution to journalArticleScientificpeer-review

Influence of temperature-induced copper diffusion on degradation of selective chromium oxy-nitride solar absorber coatings

Temperature-induced copper diffusion process and its influences on optical degradation and long-term stability of solar absorber coatings on copper substrates were investigated at intermediate temperatures of 248-500. °C. The studied absorbers were sputtered chromium oxy-nitride absorbers having tin oxide anti-reflection coatings. The absorbers were aged by means of thermal accelerated ageing studies and short-period heat treatments up to 500. °C for two hours.Ageing mechanisms and degradation of the absorbers were analysed before and after the ageing studies by optical measurements (solar absorptance with a UV/Vis/NIR spectrophotometer and thermal emittance by FTIR spectrophotometry), microstructural analysis using a field-emission scanning electron microscope (FESEM) equipped with an energy dispersive X-ray spectrometer (EDS) and a transmission electron microscope (TEM) with an EDS, composition by time-of-flight elastic recoil detection analysis (TOF-ERDA) and an X-ray photoelectron spectroscope (XPS), and adhesion by tensile test. The relation between optical degradation and diffusion mechanisms was studied using optical modelling and simulation. The results clearly revealed the mechanism of outward copper diffusion: diffusion of copper substrate atoms into the coating and through the coating to the surface, formation of copper oxide islands on the surface of the coating, and formation of voids in the substrate surface. The relation between the diffusion mechanisms and increase in thermal emittance of the absorber surface was demonstrated.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Materials Science, Research group: Surface Engineering, Research group: Materials Characterization, University of Helsinki
Contributors: Kotilainen, M., Honkanen, M., Mizohata, K., Vuoristo, P.
Number of pages: 10
Pages: 323-332
Publication date: 2016
Peer-reviewed: Yes

Publication information

Journal: Solar Energy Materials and Solar Cells
Volume: 145
ISSN (Print): 0927-0248
Ratings: 
  • Scopus rating (2016): CiteScore 4.97 SJR 1.599 SNIP 1.697
Original language: English
ASJC Scopus subject areas: Renewable Energy, Sustainability and the Environment, Electronic, Optical and Magnetic Materials, Surfaces, Coatings and Films
Keywords: Coating, Copper, Diffusion mechanisms, Solar absorber, Thermal diffusion, Void growth
Source: Scopus
Source ID: 84949090386

Research output: Contribution to journalArticleScientificpeer-review

Dissolution behavior of the bioactive glass S53P4 when sodium is replaced by potassium, and calcium with magnesium or strontium

The initial dissolution behavior of glasses based on bioactive glass S53P4 was studied with a dynamic measurement setup in a Tris-buffered solution. The glass composition was modified systematically on a molar basis by replacing sodium oxide with potassium oxide (0-100% K) and calcium oxide with magnesium (0-18% Mg) or strontium oxide (0-100% Sr). The concentrations of the ions dissolving from the glasses were measured continuously on-line in the fluid flow for 15 to 25 min using an inductively coupled plasma emission optical spectrometer. This method enabled attainment of detailed information on the initial dissolution mechanisms without the, for bioactive glasses typical, interference of apatite layer formation. The results showed that initial dissolutions of sodium and potassium were markedly higher from the mixed alkali oxide glasses than from the compositions containing only one alkali oxide. Introducing MgO in S53P4 caused a minor decrease in the dissolution rates of all ions. The glass containing 3 mol% of MgO showed the best chemical durability. In contrast, replacing CaO gradually with SrO increased the dissolution rates of all ions. The glasses with the highest replacement of CaO with SrO showed rapid release of both Sr and Na ions. The results corroborate the overall knowledge of glass durability and can be utilized to design bioactive glasses with controlled ion release rate for tissue engineering applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electronics and Communications Engineering, Research group: Biomaterials and Tissue Engineering Group, Johan Gadolin Process Chemistry Centre, Abo Akademi University, Paroc Group Oy, Åbo Akademi University
Contributors: Hupa, L., Fagerlund, S., Massera, J., Björkvik, L.
Number of pages: 6
Pages: 41-46
Publication date: 2016
Peer-reviewed: Yes
Early online date: 10 Apr 2015

Publication information

Journal: Journal of Non-Crystalline Solids
ISSN (Print): 0022-3093
Ratings: 
  • Scopus rating (2016): CiteScore 3.5 SJR 0.685 SNIP 1.154
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Ceramics and Composites, Electronic, Optical and Magnetic Materials, Materials Chemistry
Keywords: Bioactive glass, Chemical durability, Dynamic solution, Ion dissolution
Source: Scopus
Source ID: 84948073019

Research output: Contribution to journalArticleScientificpeer-review

High performance corrosion resistant coatings by novel coaxial cold- and hot-wire laser cladding methods

In the last few years, coaxial laser heads have been developed with centric wire feeding equipment, which enables the laser processing of complex-shaped objects in various applications. These newly developed laser heads are being used particularly in laser brazing experiments in the automotive industry. This study presents experimental results of using a coaxial laser head for cold- and hot-wire cladding application. The coaxial wire cladding method has significant improvements compared with the off-axis wire cladding method such as independence of the travel direction, alignment of the wire to the laser beam, and a reduced number of controlling parameters. These features are important to achieve high quality coatings. Cladding tests were conducted on mild steel with a coaxial laser wire welding head using Ni-based Inconel 625 and Thermanit 2509 super duplex stainless steel solid wires in order to determine the properties of the cladding process and the coatings deposited. The corrosion resistance of the obtained coatings was examined by long-term acetic acid salt spray (AASS) and electrochemical critical pitting temperature tests. The test results showed that by using the coaxial wire cladding method, defect-free high quality and corrosion resistant Inconel 625 and super duplex stainless steel coatings with low dilution were achieved. The average pitting temperature for Thermanit 2509 duplex coating was 75 °C in 1M NaCl solution, which was comparable to wrought 2507 duplex stainless steel. Low diluted Inconel 625 coating survived the AASS test for 2000 h without signs of corrosion.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Materials Science, Research group: Surface Engineering, Tampere University of Technology, Technology Centre Ketek Ltd.
Contributors: Pajukoski, H., Näkki, J., Thieme, S., Tuominen, J., Nowotny, S., Vuoristo, P.
Publication date: 2016
Peer-reviewed: Yes
Early online date: 8 Dec 2015

Publication information

Journal: Journal of Laser Applications
Volume: 28
Issue number: 1
Article number: 012011
ISSN (Print): 1042-346X
Ratings: 
  • Scopus rating (2016): CiteScore 1.56 SJR 0.673 SNIP 1.233
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials, Biomedical Engineering, Instrumentation
Keywords: coaxial wire feed, hot-wire laser cladding, Inconel 625, super duplex stainless steel

Bibliographical note

AUX=mol,"Pajukoski, H."

Source: Scopus
Source ID: 84950156186

Research output: Contribution to journalArticleScientificpeer-review

Linear and nonlinear light beam propagation in chiral nematic liquid crystal waveguides

We employ a thick layer of chiral nematic liquid crystals to demonstrate the evolution of a one-dimensional (1D) higher-order guided mode into a beam self-confined in both transverse dimensions at various wavelengths. We also report the experimental observation of higher-order modes guided by soliton-induced waveguides in chiral nematic liquid crystals.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Politechnika Warszawska, University of Warsaw, Aerosol Physics Laboratory, Nonlinear Optics and OptoElectronics Lab, University “Roma Tre”
Contributors: Laudyn, U. A., Kwaśny, M., Jung, P. S., Trippenbach, M., Assanto, G., Karpierz, M. A.
Number of pages: 3
Pages: 11-13
Publication date: 2016
Peer-reviewed: Yes

Publication information

Journal: Photonics Letters of Poland
Volume: 8
Issue number: 1
ISSN (Print): 2080-2242
Ratings: 
  • Scopus rating (2016): CiteScore 0.9 SJR 0.197 SNIP 0.272
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials
Source: Scopus
Source ID: 84962158419

Research output: Contribution to journalArticleScientificpeer-review

Influence of environmental conditions on EMF levels in a span of overhead transmission lines

The paper is devoted to the investigation of electromagnetic field distribution in the vicinity of overhead transmission lines under different environmental conditions, taking into account the wire sag curve in a span. A wire state equation is utilized, which allows one to calculate stresses in the wire and sags based on the known stresses and temperatures in the initial state. The results of the electric and magnetic field distribution on sample 330 kV and 110 kV transmission lines are presented. We show that the highest electromagnetic field levels are associated with the most severe environmental conditions, resulting in the highest sag.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electronics and Communications Engineering, Research group: Environmental Health, LLC Soyuzenergoproekt
Contributors: Okun, O., Kravchenko, Y., Korpinen, L.
Number of pages: 9
Pages: 163-171
Publication date: 2016
Peer-reviewed: Yes

Publication information

Journal: Progress in Electromagnetics Research C
Volume: 63
ISSN (Print): 1937-8718
Ratings: 
  • Scopus rating (2016): CiteScore 1.6 SJR 0.221 SNIP 0.597
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials
Source: Scopus
Source ID: 84971219955

Research output: Contribution to journalArticleScientificpeer-review

Decreasing the extremely low-frequency electric field exposure with a Faraday cage during work tasks from a man hoist at a 400 kV substation

Earlier studies have shown that the occupational exposure of electric fields at 400 kV substations can be higher than the low action level of 10 kV/m set by the Directive 2013/35/EU. One possibility for decreasing the occupational exposure is to surround the worker with a Faraday cage. The objective of the study was to investigate how effective a Faraday cage is in decreasing the ELF electric field exposure during work tasks from a man hoist at a 400 kV substation. First, we measured the electric field exposure while performing maintenance tasks from a man hoist. We then constructed a Faraday cage around the man hoist and measured the exposure again, with hopes that the exposure would be sufficiently reduced to create a safe working environment. The Faraday cage was constructed from a steel net 0.5m in width with 19-mm meshes. The net was made of hotdip galvanized steel wire, 1.0mm in diameter. The net and the man hoist were then grounded. The maximum electric field without the cage was 28.8 kV/m, and with the cage, it was 0.5 kV/m. The electric field, therefore, was decreased by 96.8–99.9%, validating the efficacy of Faraday cages.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electronics and Communications Engineering, Research group: Environmental Health, Fingrid Oyj
Contributors: Pirkkalainen, H., Elovaara, J., Korpinen, L.
Number of pages: 12
Pages: 55-66
Publication date: 2016
Peer-reviewed: Yes

Publication information

Journal: Progress In Electromagnetics Research M
Volume: 48
ISSN (Print): 1937-8726
Ratings: 
  • Scopus rating (2016): CiteScore 1 SJR 0.188 SNIP 0.46
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 84964820068

Research output: Contribution to journalArticleScientificpeer-review

Rapid and facile synthesis of graphene oxide quantum dots with good linear and nonlinear optical properties

We herein report a rapid and effective method for the synthesis of graphene oxide quantum dots (GOQDs) with excellent linear and nonlinear optical properties. The GOQDs were prepared by chemical cutting of graphite oxide and characterized using Fourier transform infrared spectroscopy, X-ray diffraction, UV–Vis absorption spectroscopy, Raman spectroscopy and transmission electron microscopy. The Commission International de l’Éclairage 1931 chromaticity coordinates for GOQDs (x = 0.21, y = 0.23) demonstrated that highly pure blue-light emission was achieved upon 330 nm excitation wavelength. Optical nonlinearity measurements conducted at 532 nm using 5 ns laser pulses indicated saturable absorption behavior, which tends to the onset of reverse saturable absorption as the input light fluence was increased.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Research group: Nonlinear Optics, Research area: Optics, Mahatma Gandhi University, University of Johannesburg, Ultra-Fast and Nonlinear Optical Lab, Raman Research Institute, St Teresas’s College
Contributors: Sakho, E. H. M., Oluwafemi, O. S., Perumbilavil, S., Philip, R., Kala, M. S., Thomas, S., Kalarikkal, N.
Pages: 10926–10933
Publication date: 2016
Peer-reviewed: Yes

Publication information

Journal: Journal of Materials Science: Materials in Electronics
Volume: 27
Issue number: 10
ISSN (Print): 0957-4522
Ratings: 
  • Scopus rating (2016): CiteScore 2.6 SJR 0.469 SNIP 0.802
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering
Source: Scopus
Source ID: 84975307980

Research output: Contribution to journalArticleScientificpeer-review

Compatibilization of natural rubber/nitrile rubber blends by sol–gel nano-silica generated by in situ method

Abstract: Controlled growth of in situ silica, into natural rubber (NR)/nitrile rubber (NBR) blend (40/60 composition by weight) following solution sol–gel method, results in a coherent blend morphology with enhanced composite properties. Similar composites, i.e., in situ silica-filled NR/NBR blend (40/60 by weight), showed better mechanical properties than any other composition that were prepared by soaking sol–gel method in earlier study. However, silica content in the rubber blend was limited to 20 phr (parts per hundred parts of rubber) and could not be increased under experimental condition following soaking sol–gel method. In the present work, silica content is increased (up to 30 phr) beyond that limit for the same blend composition. Accordingly, mechanical properties of the NR/NBR composites are improved. Use of a silane coupling agent, viz., bis-(3-triethoxysilylpropyl)-tetra sulfide, in the reactive sol–gel system during in situ silica generation brings in remarkable effect in silica distribution, rubber–filler interaction and mechanical properties of the composites. TEM micrographs of the selected composites reveal that silica is mostly grown at the interfacial region, when silane is used in particular. This results in further enhancement in mechanical properties and compatibility of the blend at the same silica content as evident from stress–strain and dynamic mechanical analysis studies. The reinforcement of effect in situ silica is assessed by Guth–Gold equation and modified form of Guth equation (with shape factor f = 2.53). The results are supported by the detailed studies on rheological, morphological, mechanical and viscoelastic properties of the composites. Graphical Abstract: [Figure not available: see fulltext.]

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Materials Science, Visvesvaraya National Institute of Technology, Indian Rubber Manufacturers Research Association, Department of Elastomers, Leibniz-Institut für Polymerforschung Dresden E.V., University of Kalyani
Contributors: Bansod, N. D., Kapgate, B. P., Das, C., Das, A., Basu, D., Debnath, S. C.
Number of pages: 12
Pages: 548–559
Publication date: 2016
Peer-reviewed: Yes

Publication information

Journal: JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY
Volume: 80
Issue number: 2
ISSN (Print): 0928-0707
Ratings: 
  • Scopus rating (2016): CiteScore 2.6 SJR 0.48 SNIP 0.678
Original language: English
ASJC Scopus subject areas: Chemistry(all), Condensed Matter Physics, Biomaterials, Ceramics and Composites, Electronic, Optical and Magnetic Materials, Materials Chemistry
Keywords: In situ silica, Reinforcement, Rubber blend, Rubber–filler interaction, Silane treatment, Sol–gel method
Source: Scopus
Source ID: 84974817789

Research output: Contribution to journalArticleScientificpeer-review

Rapid and sensitive detection of norovirus antibodies in human serum with a biolayer interferometry biosensor

Here, we describe the use of a biolayer interferometry biosensor for the fast and sensitive detection of virus-specific antibodies from human serum samples. Norovirus-like particles and norovirus P-particles were used to functionalise the biosensor tip. The detection of antibodies directly from serum samples was challenging, but the addition of a metal chelator (DAB) combined with an anti-human horseradish peroxidase-tagged antibody enabled enhanced detection of virus-specific antibodies in serum dilutions up to 1:100,000. Biolayer interferometry provides results faster than an ELISA, with results in as little as 10-20 min when using pre-functionalised sensors. Therefore, biolayer interferometry combined with DAB enhancement offers an attractive method for quick and sensitive quantification of biomolecules from complicated sample matrices.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Multi-scaled biodata analysis and modelling (MultiBAM), Fimlab Laboratories Ltd
Contributors: Auer, S., Koho, T., Uusi-Kerttula, H., Vesikari, T., Blazevic, V., Hytönen, V. P.
Number of pages: 8
Pages: 507-514
Publication date: 31 Dec 2015
Peer-reviewed: Yes

Publication information

Journal: Sensors and Actuators B: Chemical
Volume: 221
ISSN (Print): 0925-4005
Ratings: 
  • Scopus rating (2015): CiteScore 7.4 SJR 1.225 SNIP 1.486
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Condensed Matter Physics, Electronic, Optical and Magnetic Materials, Metals and Alloys, Surfaces, Coatings and Films, Materials Chemistry, Instrumentation
Keywords: Biolayer interferometry, Fast diagnostics, Non-labelled detection, Norovirus, P-particles, Virus-like particles (VLPs)
Source: Scopus
Source ID: 84956972181

Research output: Contribution to journalArticleScientificpeer-review

Single-source multibattery solar charger: Case study and implementation issues

In this paper, design process and functionality of a portable single-panel dual-battery solar charger prototype are presented, achieving energy density of 571Whkg-1 during a typical 3-day infantry mission. The device may instantaneously charge up to two Li-ion MR-2791 batteries, supporting plug-and-play operation. The system consists of a lightweight custom solar panel, based on 20% efficient monocrystalline photovoltaics, and an intelligent power processing module. The panel contains eight transparent polymer-encapsulated and camouflaged series-connected six solar cell packs with antiparallel diodes, allowing partial shading operation. The power processing module consists of two synchronous current-mode-controlled buck converters, digital signal processor, and a microcontroller, supporting both maximum power point tracking of the solar panel with partial shading detection and multimode charging of Li-ion packs while instantaneously communicating with the batteries. Power management algorithmic design is presented, based on ensuring system stability while supporting the required operation modes. System implementation stages and underlying issues are thoroughly discussed, and utilized hardware components are presented in detail. Experimental results of system testing under real outdoor conditions are presented to demonstrate the device functionality and energy yield capabilities.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electrical Engineering, Research area: Power engineering, Smart Energy Systems (SES), Hybrid Energy Sources Laboratory
Contributors: Gadelovits, S., Sitbon, M., Suntio, T., Kuperman, A.
Number of pages: 13
Pages: 1916-1928
Publication date: 25 Nov 2015
Peer-reviewed: Yes

Publication information

Journal: Progress in Photovoltaics: Research and Applications
Volume: 23
Issue number: 12
ISSN (Print): 1062-7995
Ratings: 
  • Scopus rating (2015): CiteScore 7.31 SJR 2.724 SNIP 3.409
Original language: English
ASJC Scopus subject areas: Renewable Energy, Sustainability and the Environment, Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Keywords: Energy density, Li-ion battery, Partial shading, Portable system, Solar charger

Research output: Contribution to journalArticleScientificpeer-review

Determination of beam incidence conditions based on the analysis of laser interference patterns

Beam incidence conditions in the formation of two-, three- and four-beam laser interference patterns are presented and studied in this paper. In a laser interference lithography (LIL) process, it is of importance to determine and control beam incidence conditions based on the analysis of laser interference patterns for system calibration as any slight change of incident angles or intensities of beams will introduce significant variations of periods and contrasts of interference patterns. In this work, interference patterns were captured by a He-Ne laser interference system under different incidence conditions, the pattern period measurement was achieved by cross-correlation with, and the pattern contrast was calculated by image processing. Subsequently, the incident angles and intensities of beams were determined based on the analysis of spatial distributions of interfering beams. As a consequence, the relationship between the beam incidence conditions and interference patterns is revealed. The proposed method is useful for the calibration of LIL processes and for reverse engineering applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Changchun University of Science and Technology, University of Bedfordshire, Xi'An Jiaotong-Liverpool University, DCSSE
Contributors: Wang, D., Wang, Z., Yue, Y., Yu, J., Tan, C., Li, D., Qiu, R., Maple, C.
Number of pages: 6
Pages: 2902-2907
Publication date: 1 Nov 2015
Peer-reviewed: Yes
Early online date: 17 Jul 2015

Publication information

Journal: Optik
Volume: 126
Issue number: 21
ISSN (Print): 0030-4026
Ratings: 
  • Scopus rating (2015): CiteScore 0.92 SJR 0.332 SNIP 0.682
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics
Keywords: Beam incidence condition, Interference lithography, Laser interference, Modulation period
Source: Scopus
Source ID: 84942373998

Research output: Contribution to journalArticleScientificpeer-review

Observation of unusual metal-semiconductor interaction and metal-induced gap states at an oxide-semiconductor interface: The case of epitaxial BaO/Ge(100) junction

Oxidation of semiconductor surfaces is known to cause defect states at oxide-semiconductor interfaces of various devices. In contrast, effects of the semiconductor interaction with non-oxygen elements at such junctions are still unclear. We present evidence for the interrelationship between a metal (non-oxygen)-semiconductor reaction and formation of the band-gap defect states at a buried oxide-semiconductor interface by investigating well-defined epitaxial BaO/Ge(100) junctions with high-resolution synchrotron-radiation photoelectron spectroscopy. The states that arise from the Ba-Ge interaction lead to Fermi-level pinning at 0.40eV above the valence band maximum, while the defect-free BaO/Ge(100) interface has a flat band structure.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Optoelectronics Research Centre, Research group: Semiconductor Technology and Applications, Frontier Photonics, Department of Physics and Astronomy, University of Turku, Russian Academy of Sciences, University of Turku, Turun Yliopisto/Turun Biomateriaalikeskus
Contributors: Kuzmin, M., Laukkanen, P., Yasir, M., Mäkelä, J., Tuominen, M., Dahl, J., Punkkinen, M. P. J., Kokko, K., Hedman, H. P., Moon, J., Punkkinen, R., Polojärvi, V., Korpijärvi, V. M., Guina, M.
Publication date: 20 Oct 2015
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 92
Issue number: 16
Article number: 165311
ISSN (Print): 1098-0121
Ratings: 
  • Scopus rating (2015): CiteScore 2.8 SJR 2.377 SNIP 1.216
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Electronic, Optical and Magnetic Materials

Bibliographical note

EXT="Kokko, K."
EXT="Laukkanen, P."
EXT="Kuzmin, M."

Source: Scopus
Source ID: 84944790567

Research output: Contribution to journalArticleScientificpeer-review

ESD qualification data used as the basis for building electrostatic discharge protected areas

ESD control programs that are based on the standards IEC61340-5-1 and ANSI/ESD S20.20 are targeted to provide safer handling of electronic parts now susceptible to damage by electrostatic discharge. However, ESD failures have occurred in EPA even when all standard control methods are met. To further improve EPAs, ESD control programs should be updated to cover all known common discharge scenarios, and multiple parallel ESD source parameters should be used to assess the level of ESD risks. In addition, a reliable ESD risk assessment should be based on discharge source circuit analysis and product sensitivity tests using the real discharge waveforms found in EPA.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electronics and Communications Engineering, Research group: Wireless Identification and Sensing Systems Research Group, Sensing Systems for Wireless Medicine (MediSense), Cascade Metrology
Contributors: Tamminen, P., Viheriäkoski, T., Sydänheimo, L., Ukkonen, L.
Number of pages: 8
Pages: 174-181
Publication date: 1 Oct 2015
Peer-reviewed: Yes

Publication information

Journal: Journal of Electrostatics
Volume: 77
Article number: 3024
ISSN (Print): 0304-3886
Ratings: 
  • Scopus rating (2015): CiteScore 2.4 SJR 0.48 SNIP 1.189
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials, Surfaces, Coatings and Films, Condensed Matter Physics, Biotechnology
Keywords: CDM, Control program, EPA, ESD, HBM, Standards
Source: Scopus
Source ID: 84940760492

Research output: Contribution to journalArticleScientificpeer-review

3GPP LTE-assisted Wi-Fi-direct: Trial implementation of live D2D technology

This paper is a first-hand summary on our comprehensive live trial of cellular-assisted device-todevice (D2D) communications currently being ratified by the standards community for next-generation mobile broadband networks. In our test implementation, we employ a full-featured 3GPP LTE network deployment and augment it with all necessary support to provide realtime D2D connectivity over emerging Wi-Fi-Direct (WFD) technology. As a result, our LTE-assisted WFD D2D system enjoys the required flexibility while meeting the existing standards in every feasible detail. Further, this paper provides an account on the extensive measurement campaign conducted with our implementation. The resulting real-world measurements from this campaign quantify the numerical effects of D2D functionality on the resultant system performance. Consequently, they shed light on the general applicability of LTE-assisted WFD solutions and associated operational ranges.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Wireless Communications and Positioning (WICO), Department of Electronics and Communications Engineering, Research group: Emerging Technologies for Nano-Bio-Info-Cogno, Brno University of Technology, Intel Corporation
Contributors: Pyattaev, A., Hosek, J., Johnsson, K., Krkos, R., Gerasimenko, M., Masek, P., Ometov, A., Andreev, S., Sedy, J., Novotny, V., Koucheryavy, Y.
Number of pages: 11
Pages: 877-887
Publication date: 1 Oct 2015
Peer-reviewed: Yes

Publication information

Journal: ETRI Journal
Volume: 37
Issue number: 5
ISSN (Print): 1225-6463
Ratings: 
  • Scopus rating (2015): CiteScore 2.5 SJR 0.393 SNIP 1.185
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Computer Science(all), Electronic, Optical and Magnetic Materials
Keywords: 3GPP LTE, Cellular assistance, Commercial opportunities, Device-to-device, Live trial, Performance measurements, Standardization, Wi-Fi-Direct
Source: Scopus
Source ID: 84942596109

Research output: Contribution to journalArticleScientificpeer-review

Construction of an Interconnected Nanostructured Carbon Black Network: Development of Highly Stretchable and Robust Elastomeric Conductors

In the present work, a strong filler-filler network of conductive carbon black was strategically established in an elastomer matrix, which leads to a unique combination of electrical and mechanical properties. The novelty of our composites was the development of a strong percolated morphology of nanostructured conducting carbon black particles by the incorporation of relatively large nonreinforcing spherical silica particles, inside the soft elastomer matrix. This technique allowed us to fabricate solution styrene butadiene rubber (S-SBR) composites with outstanding electrical conductivity of 40 S/m, tensile strength ∼10 MPa, and extensibility up to 200%. Furthermore, the electrical conductivity was strain-independent up to 50% elongation strain. The electrical conductivity was found to be unaltered after 2000 loading-unloading cycles. This is the first ever report of a robust elastomeric system with such high electrical conductivity where all the basic ingredients used were selected from well-known commercially available raw materials of rubber industry. This work directly manifests an industrially viable method for preparing high-performance elastic conductors that can be utilized in robust and flexible applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Materials Science, Engineering materials science and solutions (EMASS), Leibniz-Institut für Polymerforschung Dresden E.V., Technische Universität Dresden, Institut für Werkstoffwissenschaft, Institut für Polymerwerkstoffe E.V., Elkem AS, Silicon Materials
Contributors: Bhagavatheswaran, E. S., Parsekar, M., Das, A., Le, H. H., Wiessner, S., Stöckelhuber, K. W., Schmaucks, G., Heinrich, G.
Number of pages: 9
Pages: 21723-21731
Publication date: 17 Sep 2015
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry C
Volume: 119
Issue number: 37
ISSN (Print): 1932-7447
Ratings: 
  • Scopus rating (2015): CiteScore 7.9 SJR 1.886 SNIP 1.246
Original language: English
ASJC Scopus subject areas: Physical and Theoretical Chemistry, Electronic, Optical and Magnetic Materials, Surfaces, Coatings and Films, Energy(all)
Source: Scopus
Source ID: 84941928016

Research output: Contribution to journalArticleScientificpeer-review

Superatom Model for Ag-S Nanocluster with Delocalized Electrons

Several Ag–S nanoclusters where the cluster core comprises mixed metal (main component) and sulfur atoms show superatomic orbitals in the conduction band edge. However, there are no superatomic states, i.e., delocalized electrons, in the valence band, and the clusters in question can be labeled as “zerovalent”. We show here an example of an Ag–S cluster which fulfills the superatom model and has delocalized electrons: The recently synthesized and characterized [Ag62S12(StBu)32]2+ cluster has four delocalized valence electrons based on a simple counting rule, and we compare it to the zerovalent cluster [Ag62S13(StBu)32]4+. Our electronic structure analysis confirms the existence of superatomic states in the valence and conduction bands, but the locations of these states do not agree completely with the conventional prediction based on the spherical Jellium model. [Ag62S12(StBu)32]2+ displays the 1S2 electronic shell closure at the Fermi energy instead of the 1S21P2 configuration as suggested by its electron count. This shift of energy levels and electron shell closing has been introduced by the core–shell structure of the cluster. Our optical absorption simulation can reproduce the features observed in the experiments, and we assign these features to the transitions involving superatomic states within the conduction band.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Research group: Materials and Molecular Modeling, Computational Science X (CompX), COMP Centre of Excellence, Department of Applied Physics, Aalto University
Contributors: Goh, J. Q., Akola, J.
Number of pages: 8
Pages: 21165-21172
Publication date: 10 Sep 2015
Peer-reviewed: Yes
Early online date: 19 Aug 2015

Publication information

Journal: Journal of Physical Chemistry C
Volume: 119
Issue number: 36
ISSN (Print): 1932-7447
Ratings: 
  • Scopus rating (2015): CiteScore 7.9 SJR 1.886 SNIP 1.246
Original language: English
ASJC Scopus subject areas: Physical and Theoretical Chemistry, Electronic, Optical and Magnetic Materials, Surfaces, Coatings and Films, Energy(all)
Source: Scopus
Source ID: 84941254956

Research output: Contribution to journalArticleScientificpeer-review

Effects of thinning and heating for TiO2/AlInP junctions

TiO2/AlInP junctions are used to construct the antireflection coatings for solar cells and to passivate III-V nanostructure surfaces. The thickness of AlInP epilayer affects light absorption and appropriate Al composition determining further the energy barrier for carriers. We report on reducing the AlInP thickness by dry etching down to 10 nm without introducing harmful defect states at TiO<inf>2</inf>/AlInP interface and AlInP/GaInP interface below, according to photoluminescence. Synchrotron-radiation photoelectron spectroscopy reveals that increased oxidation of phosphorus is not harmful to TiO<inf>2</inf>/AlInP and that post heating of the material enhances AlInP oxidation and group III element segregation resulting in decreased material homogeneity.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Optoelectronics Research Centre, Research group: Semiconductor Technology and Applications, Frontier Photonics, Department of Physics and Astronomy, University of Turku, University of Turku
Contributors: Mäkelä, J., Tuominen, M., Yasir, M., Polojärvi, V., Aho, A., Tukiainen, A., Kuzmin, M., Punkkinen, M. P. J., Laukkanen, P., Kokko, K., Guina, M.
Number of pages: 4
Pages: 6-9
Publication date: 24 Aug 2015
Peer-reviewed: Yes

Publication information

Journal: Journal of Electron Spectroscopy and Related Phenomena
Volume: 205
ISSN (Print): 0368-2048
Ratings: 
  • Scopus rating (2015): CiteScore 2.7 SJR 0.817 SNIP 0.813
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Physical and Theoretical Chemistry, Spectroscopy, Condensed Matter Physics, Atomic and Molecular Physics, and Optics, Radiation
Keywords: AlInP, Passivation, Solar cell, TiO<inf>2</inf>

Bibliographical note

EXT="Laukkanen, P."
EXT="Tuominen, M."
EXT="Kuzmin, M."

Source: Scopus
Source ID: 84939833093

Research output: Contribution to journalArticleScientificpeer-review

Electrospun Black Titania Nanofibers: Influence of Hydrogen Plasma-Induced Disorder on the Electronic Structure and Photoelectrochemical Performance

This work encompasses a facile method for tailoring surface defects in electrospun TiO2 nanofibers by employing hydrogen plasma treatments. This amiable processing method was proven with SQUID, EPR, and XPS to be highly effective in generating oxygen vacancies, accompanied by the reduction of Ti4+ centers to Ti3+, resulting in the formation of black titania. The treatment temperature was found to affect the Ti3+/Ti4+ ratios and surface valence, while preserving the original 1D morphology of the titania fibers. Ab initio DFT calculations showed that a high concentration of oxygen vacancies is highly efficient in producing midgap states that enhance the system absorption over the whole visible range, as observed with UV/vis/NIR diffuse reflectance spectroscopy. Pristine TiO2 nanofibers produced a photocurrent density of similar to 0.02 mA/cm(2) at 1.23 V vs RHE, whereas the hydrogen plasma treatment resulted in up to a 10-fold increase in the photoelectrochemical performance.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Chemistry and Bioengineering, Research group: Supramolecular photochemistry, Universita degli Studi di Padova, Italy, Univ Cologne, University of Cologne, Dept Chem, Chair Inorgan & Mat Chem, Padova University, INSTM, J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Institute of Inorganic Chemistry, Catalonia Institute for Energy Research (IREC), Multiscale Materials Modelling and Tribo Simulation, CNR-IENI
Contributors: Lepcha, A., Maccato, C., Mettenbörger, A., Andreu, T., Mayrhofer, L., Walter, M., Olthof, S., Ruoko, T. P., Klein, A., Moseler, M., Meerholz, K., Morante, J. R., Barreca, D., Mathur, S.
Number of pages: 8
Pages: 18835-18842
Publication date: 20 Aug 2015
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry C
Volume: 119
Issue number: 33
ISSN (Print): 1932-7447
Ratings: 
  • Scopus rating (2015): CiteScore 7.9 SJR 1.886 SNIP 1.246
Original language: English
ASJC Scopus subject areas: Physical and Theoretical Chemistry, Electronic, Optical and Magnetic Materials, Surfaces, Coatings and Films, Energy(all)
Keywords: ROOM-TEMPERATURE, WATER, SURFACE, NANOSTRUCTURES, NANOPARTICLES, PHOTOCATALYSIS, INSULATORS, CONVERSION, DEFECTS, ARRAYS
DOIs: