Nonlinear guided waves: Preface

This special issue presents a collection of experimental and theoretical research in nonlinear waves, with emphasis on nonlinear optics, which were presented at the conference Nonlinear Guided Waves VIII held at the Hotel Victoria, Oaxaca, Mexico in April 2016. This preface provides a short history of the conference series Nonlinear Guided Waves and short introductions to the contributed papers which puts them in context.

General information

Publication status: Published
MoE publication type: B1 Article in a scientific magazine
Organisations: Photonics, Nonlinear Optics and OptoElectronics Lab, University “Roma Tre”, Optics Laboratory, Department of Physics, Tampere University of Technology, CNR-ISC, Institute for Complex Systems, University of Edinburgh
Contributors: Assanto, G., Smyth, N. F.
Publication date: 1 Dec 2016
Peer-reviewed: No

Publication information

Journal: Journal of Nonlinear Optical Physics and Materials
Volume: 25
Issue number: 4
Article number: 1650041
ISSN (Print): 0218-8635
Ratings: 
  • Scopus rating (2016): CiteScore 0.81 SJR 0.301 SNIP 0.493
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Physics and Astronomy (miscellaneous)
Keywords: discrete systems, Nonlinear optics, solitary waves, solitons
Source: Scopus
Source ID: 85011382866

Research output: Contribution to journalArticleScientific

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): 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

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

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

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

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 1.36 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

A 0.5-6MHz Active-RC LPF with Fine Gain Steps Using Binary Interpolated Resistor Banks

This paper proposes an active-RC filter that achieves a wide pseudo-continuous bandwidth-tuning range and a wide gain range with fine steps using a novel switched resistor architecture. A channelselection filter with the proposed resistor bank is designed for a multi-mode mobile-TV receiver with the 6th order Chebyshev-I topology. The bandwidth, 0.5-6 MHz with 5% steps, supports multiple mobile-TV standards with sufficient margins for process and temperature variations. The filter also accomplishes a 30-dB variable gain range with 6-dB steps, and it relaxes the dynamic range requirement of a succeeding programmable gain amplifier. The power consumption of the filter, 3.4-5.0mW, is adjustable according to the bandwidth and the signal level. The filter was fabricated with on-chip bandwidth-calibration circuitry in 0.18-μm CMOS and occupied 0.81mm2.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Sensing Systems for Wireless Medicine (MediSense), Georgia Institute of Technology, Future Communication ICs Inc., Georgia Electronic Design Center
Contributors: Beck, S., Jeong, S., Min, S., Hwang, M. W., Kim, S. T., Lim, K., Tentzeris, E. M.
Number of pages: 4
Pages: 1328-1331
Publication date: Aug 2011
Peer-reviewed: Yes

Publication information

Journal: IEICE TRANSACTIONS ON ELECTRONICS
Volume: E94-C
Issue number: 8
ISSN (Print): 0916-8524
Ratings: 
  • Scopus rating (2011): CiteScore 0.55 SJR 0.233 SNIP 0.624
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Keywords: Active filters, Calibration, Receivers, Variable-gain amplifiers
Source: Scopus
Source ID: 79961033079

Research output: Contribution to journalArticleScientificpeer-review

Absorption profile and femtosecond intraband relaxation of the intense upper Davydov component in oligothiophenes

The diffuse shape of the high-energy absorption band observed in oligothiophene crystals is interpreted in terms of Fano-type mixing between the discrete upper Davydov component at k=0 and the continuum of phonon-accompanied exciton states at other values of crystal momentum. In temporal domain, this mixing is viewed as a crystal version of radiationless transition, and is followed by subsequent intra-band exciton relaxation due to scattering processes with phonon release. The rates of energy dissipation in these latter processes, mediated by different intramolecular vibrational modes, are estimated from a simple expression based on the Fermi golden rule. Depopulation of long-lived vibronic intermediates, acting as bottlenecks, is attributed to thermally activated processes with absorption of low-frequency phonons. All essential input parameters are obtained from independent nonempirical calculations. The results are in excellent agreement both with the experimentally observed absorption band shapes and with energy-dependent femtosecond dynamics afforded by measurements of sexithiophene (6T) fluorescence and photoinduced absorption.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computational Science X (CompX), Uniwersytet Jagiellonski w Krakowie, K. Gumiński Department of Theoretical Chemistry
Contributors: Petelenz, P., Kulig, W.
Number of pages: 4
Pages: 412-415
Publication date: Feb 2011
Peer-reviewed: Yes

Publication information

Journal: Physica Status Solidi B: Basic Solid State Physics
Volume: 248
Issue number: 2
ISSN (Print): 0370-1972
Ratings: 
  • Scopus rating (2011): CiteScore 1.34 SJR 0.931 SNIP 0.723
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Electronic, Optical and Magnetic Materials
Keywords: Femtosecond spectroscopy, Intra-band relaxation, Oligothiophenes
Source: Scopus
Source ID: 79251512350

Research output: Contribution to journalArticleScientificpeer-review

Accelerator-quality HTS dipole magnet demonstrator designs for the EuCARD-2 5-T 40-mm clear aperture magnet

Future high-energy accelerators will need very high magnetic fields in the range of 20 T. The Enhanced European Coordination for Accelerator Research and Development (EuCARD-2) Work Package 10 is a collaborative push to take high-temperature superconductor (HTS) materials into an accelerator-quality demonstrator magnet. The demonstrator will produce 5 T stand alone and between 17 and 20 T when inserted into the 100-mm aperture of a Fresca-2 high-field outsert magnet. The HTS magnet will demonstrate the field strength and the field quality that can be achieved. An effective quench detection and protection system will have to be developed to operate with the HTS superconducting materials. This paper presents a ReBCO magnet design using a multistrand Roebel cable that develops a stand-alone field of 5 T in a 40-mm clear aperture and discusses the challenges associated with a good field quality using this type of material. A selection of magnet designs is presented as the result of the first phase of development.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electrical Engineering, Research area: Electromagnetics, Karlsruhe Institute of Technology, Insitute for Technical Physics, Germany, European Organization for Nuclear Research, French Atomic Energy Commission (CEA) Saclay, Physical Science Division (DSM), Institute of Research into the Fundamental Laws of the Universe (IRFU), Lawrence Berkeley National Laboratory, Karlsruhe Institute of Technology
Contributors: Kirby, G. A., Van Nugteren, J., Ballarino, A., Bottura, L., Chouika, N., Clement, S., Datskov, V., Fajardo, L., Fleiter, J., Gauthier, R., Gentini, L., Lambert, L., Lopes, M., Perez, J. C., De Rijk, G., Rijllart, A., Rossi, L., Ten Kate, H., Durante, M., Fazilleau, P., Lorin, C., Härö, E., Stenvall, A., Caspi, S., Marchevsky, M., Goldacker, W., Kario, A.
Publication date: 1 Jun 2015
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 25
Issue number: 3
Article number: 4000805
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2015): CiteScore 1.27 SJR 0.403 SNIP 1.046
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Condensed Matter Physics, Electronic, Optical and Magnetic Materials
Keywords: Accelerator magnet, EuCARD-2, HTS magnet design, quench protection, ReBCO, Superconducting Magnets, YBCO Roebel cable
Source: Scopus
Source ID: 84920829736

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

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

Adsorption and dissociation of molecular oxygen on α-Pu (0 2 0) surface: A density functional study

Molecular and dissociative oxygen adsorptions on the α-Pu (0 2 0) surface have been systematically studied using the full-potential linearized augmented-plane-wave plus local orbitals (FP-LAPWlo) basis method and the PerdewBurkeErnzerhof (PBE) exchange-correlation functional. Chemisorption energies have been optimized for the distance of the admolecule from the Pu surface and the bond length of OO atoms for four adsorption sites and three approaches of O2 admolecule to the (0 2 0) surface. Chemisorption energies have been calculated at the scalar relativistic level with no spinorbit coupling (NSOC) and at the fully relativistic level with spinorbit coupling (SOC). Dissociative adsorptions are found at the two horizontal approaches (O2 is parallel to the surface and perpendicular/parallel to a lattice vector). Hor2 (O2 is parallel to the surface and perpendicular to a lattice vector) approach at the one-fold top site is the most stable adsorption site, with chemisorption energies of 8.048 and 8.415 eV for the NSOC and SOC cases, respectively, and an OO separation of 3.70 Å. Molecular adsorption occurs at the Vert (O2 is vertical to the surface) approach of each adsorption site. The calculated work functions and net spin magnetic moments, respectively, increase and decrease in all cases upon chemisorption compared to the clean surface. The partial charges inside the muffin-tins, the difference charge density distributions, and the local density of states have been used to investigate the Pu-admolecule electronic structures and bonding mechanisms.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computational Science X (CompX), University of Texas at Arlington
Contributors: Wang, J., Ray, A. K.
Number of pages: 10
Pages: 3285-3294
Publication date: 1 Sep 2011
Peer-reviewed: Yes

Publication information

Journal: Physica B: Condensed Matter
Volume: 406
Issue number: 17
ISSN (Print): 0921-4526
Ratings: 
  • Scopus rating (2011): CiteScore 1.13 SJR 0.595 SNIP 0.797
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering
Keywords: Adsorption, Density Functional Theory, Dissociation, Oxygen, Plutonium
Source: Scopus
Source ID: 79959360654

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

A Finite Element Simulation Tool for Predicting Hysteresis Losses in Superconductors Using an H-Oriented Formulation with Cohomology Basis Functions

Currently, modelling hysteresis losses in superconductors is most often based on the H-formulation of the eddy current model (ECM) solved using the finite element method (FEM). In the H-formulation, the problem is expressed using the magnetic field intensity H and discretized using edge elements in the whole domain. Even though this approach is well established, it uses unnecessary degrees of freedom (DOFs) and introduces modelling error such as currents flowing in air regions due to finite air resistivity. In this paper, we present a modelling tool utilizing another H-oriented formulation of the ECM, making use of cohomology of the air regions. We constrain the net currents through the conductors by fixing the DOFs related to the so-called cohomology basis functions. As air regions will be truly non-conducting, DOFs and running times of these nonlinear simulations are reduced significantly as compared to the classical H-formulation. This fact is demonstrated through numerical simulations.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electrical Engineering, Research area: Electromagnetics, Microsoft Research Cambridge, UK, École Polytechnique de Montréal
Contributors: Lahtinen, V., Stenvall, A., Sirois, F., Pellikka, M.
Number of pages: 10
Pages: 2345-2354
Publication date: 22 Apr 2015
Peer-reviewed: Yes

Publication information

Journal: Journal of Superconductivity and Novel Magnetism
Volume: 28
Issue number: 8
ISSN (Print): 1557-1939
Ratings: 
  • Scopus rating (2015): CiteScore 0.83 SJR 0.318 SNIP 0.513
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Keywords: Cohomology, Finite element method, Hysteresis losses, Superconductors
Source: Scopus
Source ID: 84943356220

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

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 4.48 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

An ab initio study of PuO 2±0.25, UO 2±0.25, and U0.5Pu0.5O 2±0.25

Hybrid density functional theory has been used to systematically study the electronic, geometric, and magnetic properties of strongly correlated materials PuO 2±x, UO 2±x, and U0.5Pu0.5O 2±x with x = 0.25. The calculations have been performed using the all-electron full- potential linearized augmented plane wave plus local orbitals basis (FP-L/APW+lo) method. Each compound has been studied at the ferromagnetic (FM) and anti-ferromagnetic (AFM) configurations with and without spin-orbit coupling (SOC) and full geometry optimizations. The optimized lattice constants, bulk moduli, and band gaps are reported. Total energy calculations indicate that the ground states are AFM for all compounds studied here and the band gaps are typically higher than 1.0 eV, characteristic of semiconductors. The total energy is lowered significantly and the band gaps increase with the inclusion of SOC. The chemical bonds between the actinide metals and oxygen atoms are primarily ionic in character.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computational Science X (CompX), University of Texas at Arlington
Contributors: Ma, L., Ray, A. K.
Number of pages: 11
Pages: 103-113
Publication date: May 2011
Peer-reviewed: Yes

Publication information

Journal: European Physical Journal B
Volume: 81
Issue number: 1
ISSN (Print): 1434-6028
Ratings: 
  • Scopus rating (2011): CiteScore 1.6 SJR 1.034 SNIP 0.906
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 79960055408

Research output: Contribution to journalArticleScientificpeer-review

Analysis of uncertainties in protection heater delay time measurements and simulations in Nb3Sn high-field accelerator magnets

The quench protection of superconducting high-field accelerator magnets is presently based on protection heaters, which are activated upon quench detection to accelerate the quench propagation within the winding. Estimations of the heater delay to initiate a normal zone in the coil are essential for the protection design. During the development of Nb<inf>3</inf>Sn magnets for the LHC luminosity upgrade, protection heater delays have been measured in several experiments, and a new computational tool CoHDA (Code for Heater Delay Analysis) has been developed for heater design. Several computational quench analyses suggest that the efficiency of the present heater technology is on the borderline of protecting the magnets. Quantifying the inevitable uncertainties related to the measured and simulated delays is therefore of pivotal importance. In this paper, we analyze the uncertainties in the heater delay measurements and simulations using data from five impregnated high-field Nb<inf>3</inf>Sn magnets with different heater geometries. The results suggest that a minimum variation of 3 ms or 20% should be accounted in the heater design for coil outer surfaces and at least 10 ms or 40% in the inner surfaces due to more uncertain heater contact. We also propose a simulation criterion that gives an upper bound enclosing 90% of the measured delays for heaters on the coil outer surface.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electrical Engineering, Research area: Electromagnetics, CERN, Conseil Europeen pour la Recherche Nucleaire, Fermi National Accelerator Laboratory, Lawrence Berkeley National Laboratory
Contributors: Salmi, T., Chlachidze, G., Marchevsky, M., Bajas, H., Felice, H., Stenvall, A.
Publication date: 1 Aug 2015
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 25
Issue number: 4
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2015): CiteScore 1.27 SJR 0.403 SNIP 1.046
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Condensed Matter Physics, Electronic, Optical and Magnetic Materials
Keywords: Nb<inf>3</inf>Sn accelerator magnets, Protection heaters, Quench protection, Thermal modelling
Source: Scopus
Source ID: 84933046736

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

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

A near-infrared optoelectronic approach to detection of road conditions

We introduce and test an original approach for the optical assessment of road conditions due to various atmospheric perturbations such as the presence of ice, wet surfaces and rain. The technique is based on measuring diffused and reflected light under near infrared illumination, extracting the polarization contrast after reflection. Several tests, carried out on various types of asphalt and various thicknesses of water and ice layers, demonstrate that the system exhibits selectivity and robustness to allow the recognition of dry asphalt, water-layered, wet asphalt and asphalt with ice.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Frontier Photonics, University “Roma Tre”, Nonlinear Optics and OptoElectronics Lab
Contributors: Colace, L., Santoni, F., Assanto, G.
Number of pages: 4
Pages: 633-636
Publication date: May 2013
Peer-reviewed: Yes

Publication information

Journal: Optics and Lasers in Engineering
Volume: 51
Issue number: 5
ISSN (Print): 0143-8166
Ratings: 
  • Scopus rating (2013): CiteScore 2.4 SJR 0.864 SNIP 1.851
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics, Mechanical Engineering
Keywords: Ice detection, Near-infrared, Optical sensors
Source: Scopus
Source ID: 84874118385

Research output: Contribution to journalArticleScientificpeer-review

A new power-consumption optimization technique for two-stage operational amplifiers

This paper proposes a technique for two-stage operational amplifiers (OPAMPs) to optimize power consumption according to various channel conditions of wireless communication systems. The proposed OPAMP has the ability of reducing the quiescent current of each stage independently by introducing additional common-mode feedback, therefore more optimization is possible according to the channel conditions than conventional two-stage OPAMPs. The simulations verify the benefits of the technique. As a proof-of-concept topology, the proposed OPAMPs were used in a channel-selection filter for a multi-standard mobile-TV receiver. The power consumption of the filter, 3.4-5.0mW, was adjustable according to the bandwidth, the noise, and the jammer level. The performance of the filter meets the requirements and verifies the effectiveness of the proposed approach. The filter was fabricated in 0.18-μm CMOS and occupied 0.64mm2.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Sensing Systems for Wireless Medicine (MediSense), Georgia Institute of Technology, Georgia Electronic Design Center
Contributors: Beck, S., Kim, S. T., Lee, M., Lim, K., Laskar, J., Tentzeris, M. M.
Number of pages: 3
Pages: 1138-1140
Publication date: Jun 2011
Peer-reviewed: Yes

Publication information

Journal: IEICE TRANSACTIONS ON ELECTRONICS
Volume: E94-C
Issue number: 6
ISSN (Print): 0916-8524
Ratings: 
  • Scopus rating (2011): CiteScore 0.55 SJR 0.233 SNIP 0.624
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Keywords: Active filters, Low-power consumption, Operational amplifier, Power optimization
Source: Scopus
Source ID: 79957937458

Research output: Contribution to journalArticleScientificpeer-review

An integrated "sense-and-communicate" broad-/narrow-band optically controlled reconfigurable antenna for cognitive radio systems

An optically controlled reconfigurable antenna with operability in both wide and narrow bands is investigated for cognitive radio systems. The proposed antenna consists of a U-shaped patch for the spectrum sensing over a wide band and two open annuli for communication in narrow sub-bands within the frequency range of 3.1-10.6 GHz. The integration of narrow and wide bands devices makes the whole antenna structure compact with a dimension of 40 × 38.5 mm2. With an inherent property of being electromagnetically transparency, four appropriately placed laser-controlled photoconductive silicon switches are adopted to achieve reconfigurable frequency characteristics in the four bands of 5.8-6.8, 6.7-7.3, 7.0-8.4, and 7.9-9.2 GHz with the reflection coefficient below -10 dB. The wide-narrowband antenna is fed by two coplanar waveguides with the isolation of S21

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Sensing Systems for Wireless Medicine (MediSense), South China University of Technology, Georgia Institute of Technology
Contributors: Liu, X., Fan, Y., Tentzeris, M. M.
Number of pages: 8
Pages: 1016-1023
Publication date: 1 Apr 2015
Peer-reviewed: Yes

Publication information

Journal: Microwave and Optical Technology Letters
Volume: 57
Issue number: 4
ISSN (Print): 0895-2477
Ratings: 
  • Scopus rating (2015): CiteScore 0.72 SJR 0.318 SNIP 0.507
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
Keywords: cognitive radio, Frequency reconfigurable antenna, optical control, photoconductive switches
Source: Scopus
Source ID: 84923411745

Research output: Contribution to journalArticleScientificpeer-review

Anisotropic and strain-dependent model of magnetostriction in electrical steel sheets

This paper presents an anisotropic and mechanical strain-dependent model of magnetostriction in electrical steel sheets and its application in finite-element computations. The presented model is bidirectional and the data needed for its derivation is extracted solely from unidirectional measurements under mechanical loading. The model has six parameters that describe the magnetic and strain behavior and two parameters that describe the anisotropy. The validation of the model is carried out through measurements and computations on a single-phase transformer-like device. The comparison between computation and measurement results seems to be reasonable regardless of the fact that the magnetic behavior is modeled as single valued, isotropic, and anhysteretic. Original magnetostriction measurements are also presented and the importance of magnetostriction anisotropy in a priori isotropic electrical steel sheets is demonstrated. The model is easy to implement in existing codes and the anisotropic behavior is straightforward to modify according to a specific material.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Smart Energy Systems (SES), Aalto University, Universiteit Gent, Ghent University, Zwijnaarde, Belgium
Contributors: Belahcen, A., Singh, D., Rasilo, P., Martin, F., Ghalamestani, S. G., Vandevelde, L.
Publication date: 1 Mar 2015
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Magnetics
Volume: 51
Issue number: 3
Article number: 2001204
ISSN (Print): 0018-9464
Ratings: 
  • Scopus rating (2015): CiteScore 1.77 SJR 0.575 SNIP 1.189
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Keywords: Anisotropy, magnetomechanical effects, magnetostriction, soft magnetic materials, transformers, vibrations
Source: Scopus
Source ID: 84928813895

Research output: Contribution to journalArticleScientificpeer-review

An Optical Sensor for Volatile Amines Based on an Inkjet-Printed, Hydrogen-Bonded, Cholesteric Liquid Crystalline Film

A printable hydrogen-bonded cholesteric liquid crystal (CLC) polymer film is described, which can be used as a sensor for detection of gaseous trimethylamine (TMA). In this optical sensor the virgin CLC polymer network reflects green light. When anhydrous TMA gas penetrates the film, disruption of the hydrogen bonds occurs, with the simultaneous formation of carboxylate salts. The consequent reduction of the molecular order causes the green reflecting CLC film to become colorless. However, exposure to TMA in water-saturated nitrogen gas results in a red reflecting film. Due to the hygroscopic nature of the polymer salt that is formed by TMA, water vapor which is present in the environment is absorbed by the films. This leads to swelling of the film, resulting in an increase in pitch size and therefore a red shift of the reflection band. Interestingly, after exposure to ambient conditions, restoration of the green reflecting film takes place, showing that the sensor can be used multiple times. In a proof of principle experiment, it was shown that these CLC films can be used as optical sensors to detect volatile amines, that are produced by decaying fish. Facile determination of volatile amines in an optical fashion is possible with the use of hydrogen-bonded cholesteric liquid crystalline polymer films. Due to a response of the film to trimethylamine gas, the cholesteric reflector changes its color. This optical sensor is inkjet-printed on a foil, making it suitable for food packaging applications.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Functional Organic Materials and Devices, Eindhoven University of Technology, School of Mathematical Sciences
Contributors: Stumpel, J. E., Wouters, C., Herzer, N., Ziegler, J., Broer, D. J., Bastiaansen, C. W. M., Schenning, A. P. H. J.
Number of pages: 6
Pages: 459-464
Publication date: 2014
Peer-reviewed: Yes

Publication information

Journal: Advanced Optical Materials
Volume: 2
Issue number: 5
ISSN (Print): 2195-1071
Ratings: 
  • Scopus rating (2014): CiteScore 3.45 SJR 1.812 SNIP 1.755
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics
Keywords: Amine detection, Cholesteric liquid crystals, Inkjet printing, Sensors, Stimuli-responsive materials

Bibliographical note

EXT="Stumpel, Jelle"

Source: Scopus
Source ID: 84900420820

Research output: Contribution to journalArticleScientificpeer-review

A Novel Enhanced-Performance Flexible RFID-Enabled Embroidered Wireless Integrated Module for Sensing Applications

A novel wireless embroidered integrated platform for radio frequency identification (RFID)-enabled strain sensing that takes advantage of the nonlinear behavior of the RFID chip impedance as a function of the incident power is introduced. Due to the nonlinearity of the chip impedance as a function of the power, a large variation of chip impedance value and thus a large difference of radar cross section values for appropriately chosen power levels are achieved. Taking advantage of this idea, the sensing parameter is detected by interrogation of the sensor tag using two distinct transmitting power levels and calculating the difference of backscattered response. As a proof of concept, we applied the proposed method for the detection of an embroidered RFID-enabled strain sensor that is fabricated using electrotextiles in order to observe the variations of the magnitude and the corresponding strain levels. The proposed model for the chip impedance helps in predicting the RFID chip impedance variation for different strain conditions, an extremely important issue for RF/RFID modules and packages operating over a wide power dynamic range as well as enabling the accurate estimation of the maximum range of the RFID-enabled sensing modules for the maximum allowable power levels.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Sensing Systems for Wireless Medicine (MediSense), Department of Electronics and Communications Engineering, Research group: Wireless Identification and Sensing Systems Research Group, University of Montpellier
Contributors: Hasani, M., Vena, A., Sydänheimo, L., Tentzeris, M. M., Ukkonen, L.
Number of pages: 9
Pages: 1244-1252
Publication date: 2015
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Components, Packaging and Manufacturing Technology
Volume: 5
Issue number: 9
ISSN (Print): 2156-3950
Ratings: 
  • Scopus rating (2015): CiteScore 1.66 SJR 0.499 SNIP 1.156
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials, Industrial and Manufacturing Engineering

Bibliographical note

EXT="Vena, Arnaud"

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

Are coarse-grained models apt to detect protein thermal stability? the case of OPEP force field

We present the first investigation of the kinetic and thermodynamic stability of two homologous thermophilic and mesophilic proteins based on the coarse-grained model OPEP. The object of our investigation is a pair of G-domains of relatively large size, 200 amino acids each, with an experimental stability gap of about 40 K. The OPEP force field is able to maintain stable the fold of these relatively large proteins within the hundred-nanosecond time scale without including external constraints. This makes possible to characterize the conformational landscape of the folded protein as well as to explore the unfolding. In agreement with all-atom simulations used as a reference, we show that the conformational landscape of the thermophilic protein is characterized by a larger number of substates with slower dynamics on the network of states and more resilient to temperature increase. Moreover, we verify the stability gap between the two proteins using replica-exchange simulations and estimate a difference between the melting temperatures of about 23 K, in fair agreement with experiment. The detailed investigation of the unfolding thermodynamics allows to gain insight into the mechanism underlying the enhanced stability of the thermophile relating it to a smaller heat capacity of unfolding.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Multi-scaled biodata analysis and modelling (MultiBAM), Laboratoire de Biochimie Théorique, Institut Universitaire de France
Contributors: Kalimeri, M., Derreumaux, P., Sterpone, F.
Number of pages: 8
Pages: 494-501
Publication date: 1 Jan 2015
Peer-reviewed: Yes

Publication information

Journal: Journal of Non-Crystalline Solids
Volume: 407
ISSN (Print): 0022-3093
Ratings: 
  • Scopus rating (2015): CiteScore 1.85 SJR 0.663 SNIP 1.083
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Ceramics and Composites, Electronic, Optical and Magnetic Materials, Materials Chemistry
Keywords: Coarse-grained force field, Conformational substates network, Molecular dynamics, Protein thermodynamic stability, Thermophilic proteins
Source: Scopus
Source ID: 84922435805

Research output: Contribution to journalArticleScientificpeer-review

Aryl end-capped quaterthiophenes applied as anode interfacial layers in inverted organic solar cells

Four aryl end-capped quaterthiophene derivatives were synthesized and their material properties were studied by computational, spectroscopic, electrochemical, and thermoanalytical methods. Compounds were applied as interfacial layers between the bulk heterojunction active layer and Ag anode in inverted organic solar cells. Results show that p-cyanophenyl end-capped quaterthiophene with hexyl side chains increases both the short circuit current density and power conversion efficiency notably compared to reference interlayer material, tris-(8-hydroxyquinoline)aluminum. The improved cell performance was attributed to the optimal positions of the highest occupied molecular orbital and the lowest unoccupied molecular orbital (LUMO) of this material, relative to those of the photoactive electron donor poly(3-hexylthiophene) and Ag anode, and evenly distributed LUMO. In addition, the use of these materials as an anode interfacial layer increases the absorption of the solar cell, which could contribute to the formation of excitons and additional current production by the cell.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Chemistry and Bioengineering, Research group: Supramolecular photochemistry, Frontier Photonics, University of Oulu, Department of Chemistry and Mathematics, Faculty of Petroleum and Mining Engineering, Suez University
Contributors: Heiskanen, J. P., Manninen, V. M., Pankov, D., Omar, W. A. E., Kastinen, T., Hukka, T. I., Lemmetyinen, H. J., Hormi, O. E. O.
Number of pages: 11
Pages: 196-206
Publication date: 1 Jan 2015
Peer-reviewed: Yes

Publication information

Journal: Thin Solid Films
Volume: 574
ISSN (Print): 0040-6090
Ratings: 
  • Scopus rating (2015): CiteScore 1.84 SJR 0.68 SNIP 0.923
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: Anode interfacial layer, Bulk heterojunction, Computational research, Inverted organic solar cell, Oligothiophene, Spectroscopy, Suzuki-Miyaura

Bibliographical note

EXT="Heiskanen, J. P."

Source: Scopus
Source ID: 84921286591

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 2.4 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

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 2.7 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

Block copolymer lithography: Feature size control and extension by an over-etch technique

Block copolymer lithography based on block copolymer (BCP) self-assembly can be used to develop soft mask nanoscale templates for subsequent pattern transfer to generate substrate features. Self-assembly of lamellar polystyrene-b-polymethylmethacrylate BCP of varying molecular weights to generate silicon nanoscale features is reported here. It has also been demonstrated that the feature size can be controlled by a plasma over-etch process and discussed.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Frontier Photonics, Materials Chemistry and Analysis Group, University College Cork, Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College Dublin, Tyndall National Institute at National University of Ireland, Cork, Collinstown Industrial Estate
Contributors: Rasappa, S., Borah, D., Senthamaraikannan, R., Faulkner, C. C., Shaw, M. T., Gleeson, P., Holmes, J. D., Morris, M. A.
Number of pages: 6
Pages: 318-323
Publication date: 1 Nov 2012
Peer-reviewed: Yes

Publication information

Journal: Thin Solid Films
Volume: 522
ISSN (Print): 0040-6090
Ratings: 
  • Scopus rating (2012): CiteScore 1.86 SJR 0.897 SNIP 1.153
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: Block copolymer, Lithography, Over-etching, Plasma etching, Polystyrene-b-polymethylmethacrylate, Self-assembly, Silicon nanowires
Source: Scopus
Source ID: 84868593394

Research output: Contribution to journalArticleScientificpeer-review

Boron delta-doping dependence on Si/SiGe resonant interband tunneling diodes grown by chemical vapor deposition

Si/SiGe resonant interband tunnel diodes (RITD) were fabricated using CVD on 200-mm silicon wafers. The RITD devices consist of a p +-i-n + structure with δ-doped quantum wells providing resonant interband tunneling through a nominally intrinsic Si/SiGe region. The vapor-phase doping technique was used to obtain abrupt degenerate doping profiles. The boron doping in the δ-doped region was varied, and its effect on peak current density J p and peak-to-valley current ratio (PVCR) was studied. As the flow rate is reduced, J p was found to reduce while the PVCR initially increases and then decreases. Device simulations were performed using the ATLAS simulator developed by SILVACO to interpret the results. A maximum PVCR of 2.95 was obtained, and the highest J p recorded was 600 A/cm 2. This is the highest reported PVCR for any CVD-grown Si/SiGe RITD.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Augmented Human Activities (AHA), Ohio State University, Department of Electrical and Computer Engineering, Imec
Contributors: Ramesh, A., Growden, T. A., Berger, P. R., Loo, R., Vandervorst, W., Douhard, B., Caymax, M.
Number of pages: 8
Pages: 602-609
Publication date: Mar 2012
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Electron Devices
Volume: 59
Issue number: 3
ISSN (Print): 0018-9383
Ratings: 
  • Scopus rating (2012): CiteScore 2.66 SJR 1.317 SNIP 1.736
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Keywords: Band-to-band tunneling, chemical vapor deposition (CVD), Delta doping, resonant interband tunnel diodes (RITD), resonant tunneling, Si, SiGe
Source: Scopus
Source ID: 84857652658

Research output: Contribution to journalArticleScientificpeer-review

Bringing High-Performance GaInNAsSb/GaAs SOAs to True Data Applications

We experimentally demonstrate the high-speed data processing capabilities of a GaInNAsSb semiconductor optical amplifier operating at 1.55 μm. The investigated structure exhibits good thermal characteristics and fast gain dynamics with 10%-90% recovery time of 55 ps. Successful wavelength conversion of 10-Gb/s signals is reported. A maximum power penalty of <2.4 dB for return to zero formatting and of 1.9 dB for nonreturn to zero is demonstrated.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Optoelectronics Research Centre, Research group: Semiconductor Technology and Applications, Research group: Nanophotonics, Frontier Photonics, Photonics Research Communications Laboratory, National Technological University of Athens
Contributors: Giannoulis, G., Korpijärvi, V., Iliadis, N., Mäkelä, J., Viheriälä, J., Apostolopoulos, D., Guina, M., Avramopoulos, H.
Number of pages: 4
Pages: 1691-1694
Publication date: 15 Aug 2015
Peer-reviewed: Yes

Publication information

Journal: IEEE Photonics Technology Letters
Volume: 27
Issue number: 16
Article number: 7113825
ISSN (Print): 1041-1135
Ratings: 
  • Scopus rating (2015): CiteScore 2.62 SJR 1.19 SNIP 1.254
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials
Keywords: dilute nitrides, Photonic integration, semiconductor optical amplifier (SOA), wavelength conversion
Source: Scopus
Source ID: 84937146617

Research output: Contribution to journalArticleScientificpeer-review

Broadband finite-Difference Time-Domain modeling of plasmonic organic photovoltaics

We develop accurate finite-difference time-domain (FDTD) modeling of polymer bulk heterojunction solar cells containing Ag nanoparticles between the holetransporting layer and the transparent conducting oxidecoated glass substrate in the wavelength range of 300 nm to 800 nm. The Drude dispersion modeling technique is used to model the frequency dispersion behavior of Agnanoparticles, the hole-transporting layer, and indium tin oxide. The perfectly matched layer boundary condition is used for the top and bottom regions of the computational domain, and the periodic boundary condition is used for the lateral regions of the same domain. The developed FDTD modeling is employed to investigate the effect of geometrical parameters of Ag nanospheres on electromagnetic fields in devices. Although negative plasmonic effects are observed in the considered device, absorption enhancement can be achieved when favorable geometrical parameters are obtained.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Augmented Human Activities (AHA), University Seoul, Ohio State University, Ajou University
Contributors: Jung, K. Y., Yoon, W. J., Park, Y. B., Berger, P. R., Teixeira, F. L.
Number of pages: 8
Pages: 654-661
Publication date: 2014
Peer-reviewed: Yes

Publication information

Journal: ETRI Journal
Volume: 36
Issue number: 4
ISSN (Print): 1225-6463
Ratings: 
  • Scopus rating (2014): CiteScore 1.45 SJR 0.442 SNIP 1.395
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Computer Science(all), Electronic, Optical and Magnetic Materials
Keywords: FDTD, Organic photovoltaics, Plasmonics
Source: Scopus
Source ID: 84905972119

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

Calculated electronic density of states and structural properties of tetrahedral amorphous carbon

A series of tetrahedral amorphous carbon structures with different microscopic mass densities was generated by calculations based on the density functional theory with a local density approximation and using a method of melting-cooling cycles. A detailed investigation of the properties of the simulated structures has been carried out. Particularly, the short-range order, nearest neighbour distances, fractions of sp1, sp2 and sp3 sites, average C-C-C bond angles and electronic density of states have been analyzed. The simulated structures and calculated properties are in good agreement with those obtained by others and with the experimental data. An unexpected observation is the presence of planar structures, which are typical for graphite, in the sample with low density. In addition, the nearest neighbour distance in the sample with mass density 3.54 g/cm3 is different from those reported previously. Possibilities to compare the density of states obtained from the simulations with the experimental results from scanning tunnelling spectroscopy and X-ray near edge spectrum are discussed.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: University of Oulu, Department of Physical Sciences
Contributors: Koivusaari, K. J., Rantala, T. T., Leppävuori, S.
Number of pages: 5
Pages: 736-740
Publication date: Apr 2000
Peer-reviewed: Yes

Publication information

Journal: Diamond and Related Materials
Volume: 9
Issue number: 3
ISSN (Print): 0925-9635
Ratings: 
  • Scopus rating (2000): SJR 1.393 SNIP 0.943
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Materials Chemistry, Surfaces, Coatings and Films, Surfaces and Interfaces
Source: Scopus
Source ID: 0033748066

Research output: Contribution to journalArticleScientificpeer-review

Calculation of the scalar diffraction field from curved surfaces by decomposing the three-dimensional field into a sum of Gaussian beams

We present a local Gaussian beam decomposition method for calculating the scalar diffraction field due to a twodimensional field specified on a curved surface. We write the three-dimensional field as a sum of Gaussian beams that propagate toward different directions and whose waist positions are taken at discrete points on the curved surface. The discrete positions of the beam waists are obtained by sampling the curved surface such that transversal components of the positions form a regular grid. The modulated Gaussian window functions corresponding to Gaussian beams are placed on the transversal planes that pass through the discrete beam-waist position. The coefficients of the Gaussian beams are found by solving the linear system of equations where the columns of the system matrix represent the field patterns that the Gaussian beams produce on the given curved surface. As a result of using local beams in the expansion, we end up with sparse system matrices. The sparsity of the system matrices provides important advantages in terms of computational complexity and memory allocation while solving the system of linear equations.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Signal Processing Research Community (SPRC), Bilkent University
Contributors: Şahin, E., Onural, L.
Number of pages: 10
Pages: 527-536
Publication date: 2013
Peer-reviewed: Yes

Publication information

Journal: Journal of the Optical Society of America A: Optics Image Science and Vision
Volume: 30
Issue number: 3
ISSN (Print): 1084-7529
Ratings: 
  • Scopus rating (2013): CiteScore 1.66 SJR 1.046 SNIP 1.331
Original language: English
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials, Computer Vision and Pattern Recognition
Source: Scopus
Source ID: 84875512966

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 1.99 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

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

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

General information

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

Publication information

Journal: Optica
Volume: 5
Issue number: 11
ISSN (Print): 2334-2536
Ratings: 
  • Scopus rating (2018): CiteScore 10.26 SJR 4.914 SNIP 3.162
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

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 4.58 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

Cavity formation in split ring resonators

We report that it is possible to obtain a cavity structure by the deformation of a unit cell of an split ring resonator (SRR) structure. We presented the Q-factor of the cavity resonance as 192 for an SRR-based single cavity. Subsequently, we brought two and three cavities together with an intercavity distance of two metamaterial unit cells and investigated the transmission spectrum of SRR-based interacting 2-cavity and 3-cavity systems. The splitting of eigenmodes due to the interaction between the localized electromagnetic cavity modes was observed. Eventually, in taking full advantage of the effective medium theory, we modeled SRR-based cavities as 1D Fabry-Perot reflectors (FPRs) with a subwavelength cavity at the center. Finally, we observed that at the cavity resonance, the effective group velocity was reduced by a factor of 67 for an SRR-based single cavity compared to the electromagnetic waves propagating in free space.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Nanotechnology Research Center, Harvard University
Contributors: Caglayan, H., Bulu, I., Loncar, M., Ozbay, E.
Number of pages: 5
Pages: 200-204
Publication date: Dec 2008
Peer-reviewed: Yes

Publication information

Journal: Photonics and Nanostructures - Fundamentals and Applications
Volume: 6
Issue number: 3-4
ISSN (Print): 1569-4410
Ratings: 
  • Scopus rating (2008): SJR 1.212 SNIP 1.169
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Hardware and Architecture, Condensed Matter Physics, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials
Keywords: Cavity, Metamaterials, Split rind resonator

Bibliographical note

EXT="Caglayan, Humeyra"

Source: Scopus
Source ID: 56049112536

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 2.02 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

Cold test results of the LARP HQ Nb3Sn quadrupole magnet at 1.9 K

The high gradient quadrupole magnet is a 120-mm-aperture, 1-m-long Nb 3Sn quadrupole developed by the LHC Accelerator Research Program collaboration in support of the High-Luminosity LHC project. Several tests were performed at Lawrence Berkeley National Laboratory in 2010-2011 achieving a maximum gradient of 170 T/m at 4.4 K. As a next step in the program, the latest model (HQ01e) was sent to CERN for testing at 1.9 K. As part of this test campaign, the magnet training has been done up to a maximum current of 16.2 kA corresponding to 85% of the short sample limit. The ramp rate dependence of the quench current is also identified. The efficiency of the quench heaters is then studied at 4.2 K and at 1.9 K. The analyses of the magnet resistance evolution during fast current discharge showed evidence of quench whereas high energy quenches have been successfully achieved and sustained with no dump resistor.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research area: Electromagnetics, European Organization for Nuclear Research, Fermi National Accelerator Laboratory, Brookhaven National Laboratory, Lawrence Berkeley National Laboratory
Contributors: Bajas, H., Ambrosio, G., Anerella, M., Bajko, M., Bossert, R., Caspi, S., Chiuchiolo, A., Chlachidze, G., Dietderich, D., Dunkel, O., Felice, H., Ferracin, P., Feuvrier, J., Fiscarelli, L., Ghosh, A., Giloux, C., Godeke, A., Hafalia, A. R., Marchevsky, M., Russenschuck, S., Sabbi, G. L., Salmi, T., Schmalzle, J., Todesco, E., Wanderer, P., Wang, X., Yu, M.
Publication date: 2013
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 23
Issue number: 3
Article number: 4002606
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2013): CiteScore 1.32 SJR 0.443 SNIP 1.148
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: High gradient quadrupole (HQ), LHC Accelerator Research Program (LARP), magnet protection, NbSnquadrupole
Source: Scopus
Source ID: 84878130018

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 2.9 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

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

Comparison of the optical, thermal and structural properties of Ge-Sb-S thin films deposited using thermal evaporation and pulsed laser deposition techniques

Thin films of Ge 23Sb 7S 70 glass were prepared by thermal evaporation (TE) and pulsed laser deposition (PLD) techniques. We measured their thermal, optical and structural properties and compared with those of the parent bulk. The probe penetration temperature (T p) of the bulk glass, measured using a micro-thermal analyzer, was found to be 412 ± 10 °C, while those of the TE and PLD films were 468 and 470 ± 10 °C, respectively. The refractive index of the bulk and thin films was measured by ellipsometry and ultraviolet-visible-near infrared transmission spectroscopy, and we show that the films have similar refractive indices, which are lower than those of the parent bulk glass. Using micro-Raman spectroscopy, the structure of the film was investigated. The films contain homopolar Ge-Ge bonds and a lower number of homopolar S-S bonds compared to bulk material, which leads to an increase in the proportion of corner shared GeS 4/2 units in the films as compared to the bulk glass. Comparison of structural entities associated with each deposition process showed that the TE film possesses a lower number of S-S bonds and a slightly higher number of SbS 3/2 units compared to the PLD film. These structural changes lead to a more interconnected glass network, and therefore to a higher viscosity at elevated temperatures, as well as a higher refractive index, presumably through increased density. Post-deposition of annealing of these films causes their thermal and optical properties to revert to a more bulk-like state, suggesting that these property differences are due to a difference in the thermal histories of the bulk and film glass networks. For the first time to our knowledge, the refractive index of the bulk glass in the 0.6-10.6 μm range, measured using the prism coupling technique, is also presented.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Frontier Photonics, Clemson University, Massachusetts Institute of Technology, School of Materials Science and Engineering/COMSET
Contributors: Musgraves, J. D., Carlie, N., Hu, J., Petit, L., Agarwal, A., Kimerling, L. C., Richardson, K. A.
Number of pages: 8
Pages: 5032-5039
Publication date: Jul 2011
Peer-reviewed: Yes

Publication information

Journal: Acta Materialia
Volume: 59
Issue number: 12
ISSN (Print): 1359-6454
Ratings: 
  • Scopus rating (2011): CiteScore 4.27 SJR 3.215 SNIP 2.757
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Metals and Alloys, Polymers and Plastics, Electronic, Optical and Magnetic Materials
Keywords: Chalcogenide glass, Micro-thermal analysis, Pulsed laser deposition, Thermal evaporation, Thin films
Source: Scopus
Source ID: 79958132088

Research output: Contribution to journalArticleScientificpeer-review

Comparison of three light doses in the photodynamic treatment of actinic keratosis using mathematical modeling

Photodynamic therapy (PDT) is an emerging treatment modality for various diseases, especially for cancer therapy. Although high efficacy is demonstrated for PDT using standardized protocols in nonhyperkeratotic actinic keratoses, alternative light doses expected to increase efficiency, to reduce adverse effects or to expand the use of PDT, are still being evaluated and refined. We propose a comparison of the three most common light doses in the treatment of actinic keratosis with 5-aminolevulinic acid PDT through mathematical modeling. The proposed model is based on an iterative procedure that involves determination of the local fluence rate, updating of the local optical properties, and estimation of the local damage induced by the therapy. This model was applied on a simplified skin sample model including an actinic keratosis lesion, with three different light doses (red light dose, 37 J/cm2, 75 mW/cm2, 500 s; blue light dose, 10 J/cm2, 10 mW/cm2, 1000 s; and daylight dose, 9000 s). Results analysis shows that the three studied light doses, although all efficient, lead to variable local damage. Defining reference damage enables the nonoptimal parameters for the current light doses to be refined and the treatment to be more suitable

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Frontier Photonics, Univ Paris 06, Centre National de la Recherche Scientifique (CNRS), Pierre & Marie Curie University - Paris 6, Institut de Recherche pour le Developpement (IRD), Inria, Institut National de la Sante et de la Recherche Medicale (Inserm), Univ Sorbonne, CNRS,ICM,UMR S 1127,UMR 7225,U1127, INSERM,Inria Paris Rocquencourt,Inst Cerveau & Mo, Univ Lille Nord de France, Lille University Hospital - CHRU
Contributors: Vignion-Dewalle, A. S., Betrouni, N., Tylcz, J. B., Vermandel, M., Mortier, L., Mordon, S.
Publication date: 1 May 2015
Peer-reviewed: Yes

Publication information

Journal: JOURNAL OF BIOMEDICAL OPTICS
Volume: 20
Issue number: 5
Article number: 058001
ISSN (Print): 1083-3668
Ratings: 
  • Scopus rating (2015): CiteScore 2.68 SJR 1.173 SNIP 1.276
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Biomaterials, Biomedical Engineering
Keywords: light doses comparison, mathematical modeling, photodynamic therapy, protoporphyrin IX
Source: Scopus
Source ID: 84930001957

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 1.53 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

Composition dependent growth dynamics in molecular beam epitaxy of GaInNAs solar cells

We have investigated the role of the nitrogen content, the growth parameters, and the annealing processes involved in molecular beam epitaxy of GaInNAs solar cells lattice-matched to GaAs. The nitrogen composition was varied between 1% and 5%. The influence of the growth temperature was assessed by performing photoluminescence, atomic force microscopy, X-ray diffraction, reflection high-energy electron diffraction, quantum efficiency and light-biased current-voltage measurements. The growth temperature ensuring the best cell parameters was found to be 440 C. At this temperature we were able to incorporate up to 4% of nitrogen and achieve a good material quality. Further increase of the N composition to 5% led to phase separation. For the lattice matched samples grown within the optimal temperature range, we have identified a clear (1×3) surface reconstruction. Using the optimized growth we have demonstrated a GaInNAs p-i-n solar cell structure containing 4% nitrogen, that exhibited a short-circuit current density as high as 33.8 mA/cm2 in respect to effective area illuminated. These measurements have been performed under real sun AM1.5 (~1000 W/m2) illumination. © 2014 Elsevier B.V.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Optoelectronics Research Centre, Frontier Photonics, Department of Physics and Astronomy, University of Turku, Turun Yliopisto/Turun Biomateriaalikeskus
Contributors: Aho, A., Polojärvi, V., Korpijärvi, V. M., Salmi, J., Tukiainen, A., Laukkanen, P., Guina, M.
Number of pages: 9
Pages: 150-158
Publication date: May 2014
Peer-reviewed: Yes

Publication information

Journal: Solar Energy Materials and Solar Cells
Volume: 124
ISSN (Print): 0927-0248
Ratings: 
  • Scopus rating (2014): CiteScore 5.87 SJR 2.19 SNIP 2.368
Original language: English
ASJC Scopus subject areas: Renewable Energy, Sustainability and the Environment, Electronic, Optical and Magnetic Materials, Surfaces, Coatings and Films
Keywords: Concentrated photovoltaics, Dilute nitrides, GaInNAs, Multi-junction solar cells, Plasma-assisted molecular beam epitaxy

Bibliographical note

Contribution: organisation=orc,FACT1=1<br/>Portfolio EDEND: 2014-04-29<br/>Publisher name: Elsevier

Source: researchoutputwizard
Source ID: 58

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 9.05 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

Computation of torque of an electrical machine with different types of finite element mesh in the air gap

In the numerical analysis of electrical machines, accurate computation of the electromagnetic torque is desired. Maxwell stress tensor method and Coulomb's method are the most commonly used methods for computing torque numerically. However, several other methods have also been developed and are being used. These methods are observed to have several accuracy issues related to the finite element discretization used in the air gap of the machine. In this paper, the effect of various finite element meshes in the air gap of the machine and the effect of the shape of the elements used to compute the torque are studied and discussed. This paper carefully compares the torques obtained from a direct method and a method based on the power balance of the machine.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Smart Energy Systems (SES), Aalto University
Contributors: Silwal, B., Rasilo, P., Perkkio, L., Oksman, M., Hannukainen, A., Eirola, T., Arkkio, A.
Publication date: 1 Dec 2014
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Magnetics
Volume: 50
Issue number: 12
Article number: 8105909
ISSN (Print): 0018-9464
Ratings: 
  • Scopus rating (2014): CiteScore 1.68 SJR 0.696 SNIP 1.45
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Keywords: Electromagnetic torque, energy balance, finite element method, induction machine, mesh
Source: Scopus
Source ID: 84919467497

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

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 4.68 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

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

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

Cysteine-tagged chimeric avidin forms high binding capacity layers directly on gold

Cysteine-tagged, genetically engineered avidin named ChiAvd-Cys and wild-type avidin form monolayers or bilayer structures when immobilised directly on gold. Non-specific binding can be reduced by a post-treatment of the avidin layers with a N-[tris(hydroxymethyl)methyl]-acrylamide (pTHMMAA) polymer. ChiAvd-Cys showed excellent activity when immobilised on gold. About 70% of the ChiAvd-Cys molecules were able to bind two biotinylated green fluorescent proteins (per avidin tetramer). Amino-biotinylated antibody F(ab′) 2 fragments could be bound to every 4th and 8th ChiAvd-Cys and wild-type avidin molecule, respectively, whereas on average one thiol-biotinylated antibody Fab′-fragment was bound to every ChiAvd-Cys. Antigen binding to the thiol-biotinylated Fab′-fragment bound to the ChiAvd-Cys/pTHMMAA layer was almost twice compared to that of the amino-biotinylated F(ab′) 2-fragments. The high antigen binding was due to a site-directed orientation of the thiol-biotinylated fragments. The ChiAvd-Cys/pTHMMAA layers offer high capacity that may be used to couple biotinylated compounds on biosensor surfaces.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Multi-scaled biodata analysis and modelling (MultiBAM), VTT Technical Research Centre of Finland, School of Management (JKK), Adult Stem Cells, Tampere University Hospital
Contributors: Vikholm-Lundin, I., Auer, S., Paakkunainen, M., Määttä, J. A. E., Munter, T., Leppiniemi, J., Hytönen, V. P., Tappura, K.
Number of pages: 9
Pages: 440-448
Publication date: Aug 2012
Peer-reviewed: Yes

Publication information

Journal: Sensors and Actuators B: Chemical
Volume: 171-172
ISSN (Print): 0925-4005
Ratings: 
  • Scopus rating (2012): CiteScore 3.92 SJR 1.412 SNIP 1.653
Original language: English
ASJC Scopus subject areas: Instrumentation, Materials Chemistry, Surfaces, Coatings and Films, Metals and Alloys, Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Avidin, Biotin, Cysteine tagged, Non-specific binding, Self-assembled monolayer
Source: Scopus
Source ID: 84864284365

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 0.67 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

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): 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

Demonstration of optical nonlinearity in InGaAsP/InP passive waveguides

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

General information

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

Publication information

Journal: Optical Materials
Volume: 84
ISSN (Print): 0925-3467
Ratings: 
  • Scopus rating (2018): CiteScore 2.6 SJR 0.59 SNIP 1.025
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

Design, fabrication, and testing of a low AC-loss conduction-cooled cryostat for magnetization loss measurement apparatus

Conduction cooling has become a viable alternative for cooling superconducting devices. However, the thermal pathways of a conduction-cooled cryostat can be problematic for applications where time-varying magnetic fields are present. Such alternating magnetic fields are present, e.g., in a magnetization ac-loss measurement system. The losses in the thermal pathways are unwanted as they increase the heat load into the cryostat and interfere with the measurement. To solve this challenge, a conduction-cooled cryostat with special attention in limiting eddy-current losses in the cryostat structures was constructed. The design process is illustrated in detail starting from the specifications and proceeding through the fabrication of individual components. The loss dissipated in the cryostat is experimentally examined, and the finished conduction-cooled magnetization loss measurement system is demonstrated by characterizing a multifilamentary \hbox{MgB}-{2} conductor.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Electrical Engineering, Research area: Electromagnetics, Lappeenranta University of Technology, LUT Energy, Slovak Academy of Sciences
Contributors: Järvelä, J., Lyly, M., Stenvall, A., Juntunen, R., Souc, J., Mikkonen, R.
Publication date: 1 Feb 2015
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 25
Issue number: 1
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2015): CiteScore 1.27 SJR 0.403 SNIP 1.046
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Condensed Matter Physics, Electronic, Optical and Magnetic Materials
Source: Scopus
Source ID: 84916620705

Research output: Contribution to journalArticleScientificpeer-review

Designing materials with desired electromagnetic properties

In this work, we suggest and demonstrate a robust method to tune the plasma frequencies of wire mediums. The method we suggest involves the use of two or more wire arrangements in the unit cell. By incorporating the method we suggested it is possible to tune the plasma frequencies of wire mediums effectively by use of lower metal densities. In addition, we study the effective permittivities and permeabilities of labyrinth based metamaterials. Our results show that the effective permeability of the labyrinth based metamaterial medium is negative above a certain frequency. The results of the effective permittivity calculations for the labyrinth based metamaterial medium reveal that the labyrinth structure exhibits a strong dielectric response near the magnetic resonance frequency. Finally, we design labyrinth based left-handed mediums that have several desired properties such as simultaneous μ, ε = -1 and μ, ε = 0.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Bilkent University, Nanotechnology Research Center
Contributors: Bulu, I., Caglayan, H., Ozbay, E.
Number of pages: 5
Pages: 2611-2615
Publication date: Dec 2006
Peer-reviewed: Yes

Publication information

Journal: Microwave and Optical Technology Letters
Volume: 48
Issue number: 12
ISSN (Print): 0895-2477
Ratings: 
  • Scopus rating (2006): SJR 0.564 SNIP 0.685
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Condensed Matter Physics, Electrical and Electronic Engineering
Keywords: Effective medium, Metamaterials, Negative index, Split ring

Bibliographical note

EXT="Caglayan, Humeyra"

Source: Scopus
Source ID: 33750556414

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

Detection of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) by displacement of antibodies

A molecular layer with low non-specific binding enabling determination of low concentrations of 3,4-methylenedioxymethamphetamine (MDMA) by the displacement of antibodies has been developed. Antibody Fab′-fragments at various concentrations have been site-directly immobilised on gold and intercalated with a hydrophilic non-ionic polymer that reduces non-specific binding. Bovine serum albumin conjugated with MDMA and various concentrations of anti-MDMA antibodies were bound to the layer. The amount of conjugates and antibodies bound was dependent on the amount of Fab′-fragments in the layer. Antibodies were also bound to the conjugates physisorbed directly onto the gold surface and in mixtures with the polymer or with a lipoamide. A high displacement of antibodies was observed by surface plasmon resonance (SPR) on interaction of MDMA with the different layers in buffer solution. No displacement could, however, be observed in saliva with the pure conjugate layer because of a high non-specific binding of proteins. When the conjugates were coupled to the surface through the antibody Fab-fragment/polymer layer, MDMA concentrations as low as 0.02 ng mL-1 (0.14 nM) could easily be detected in buffer. In diluted saliva the lowest limit of detection was 0.4 ng mL-1 enabling determination of drugs from saliva with a cut-off concentration of 2 ng mL-1. The molecular layer of antibody Fab′-fragments and polymer thus shows great potential for binding conjugates and antibodies that can be displaced on the interaction with very low concentrations of small-sized molecules. A low non-specific binding is guaranteed by the presence of the hydrophilic polymer.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Multi-scaled biodata analysis and modelling (MultiBAM), VTT Technical Research Centre of Finland, Biosensors Applications AB
Contributors: Vikholm-Lundin, I., Auer, S., Hellgren, A. C.
Number of pages: 7
Pages: 28-34
Publication date: 10 Aug 2011
Peer-reviewed: Yes

Publication information

Journal: Sensors and Actuators B: Chemical
Volume: 156
Issue number: 1
ISSN (Print): 0925-4005
Ratings: 
  • Scopus rating (2011): CiteScore 4.08 SJR 1.485 SNIP 1.752
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: Antibody displacement, Drugs of abuse, Ecstasy, Immobilisation, MDMA, Surface plasmon resonance
Source: Scopus
Source ID: 79957806721

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

Development of a new illumination procedure for photodynamic therapy of the abdominal cavity

A homogeneous illumination of intra-abdominal organs is essential for successful photodynamic therapy of the abdominal cavity. Considering the current lack of outstanding light-delivery systems, a new illumination procedure was assessed. A rat model of peritoneal carcinomatosis was used. Four hours after intraperitoneal injection of hexaminolevulinate, a square illuminating panel connected to a 635-nm laser source was inserted vertically into the abdominal cavity. The abdominal incision was sutured and a pneumoperitoneum created prior to illumination. Light dosimetry was based on the calculation of the peritoneal surface by MRI. The rats were treated with a light dose of 20,10, 5 or 2.5 J/cm2 administered continuously with an irradiance of 7 mW/cm 2. The homogeneity of the cavity illumination was assessed by quantification of the photobleaching of the tumor lesions according to their localization and by scoring of that of the liver and of the bowel immediately after treatment. Photobleaching quantification for tumor lesions relied on the calculation of the fluorescence intensity ratio (after/before treatment) after recording of the lesions during blue-light laparoscopy and determination of their fluorescence intensity with Sigmascan Pro software. The procedure led to a homogeneous treatment of the abdominal cavity. No statistical difference was observed for the photobleaching values according to the localization of the lesions on the peritoneum (p = 0.59) and photobleaching of the liver and of the intestine was homogeneous. We conclude that this procedure can successfully treat the major sites involved in peritoneal carcinomatosis.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Frontier Photonics, Lille University Hospital - CHRU, Univ Lille Nord de France, GDR 3049
Contributors: Cuyon, L., Lesage, J. C., Betrouni, N., Mordon, S.
Publication date: Mar 2012
Peer-reviewed: Yes

Publication information

Journal: JOURNAL OF BIOMEDICAL OPTICS
Volume: 17
Issue number: 3
Article number: 038001
ISSN (Print): 1083-3668
Ratings: 
  • Scopus rating (2012): CiteScore 2.55 SJR 1.292 SNIP 1.329
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Biomaterials, Biomedical Engineering
Keywords: Hexaminolevulinate, Light dosimetry, Peritoneal carcinomatosis, Photobleaching, Photodynamic therapy
Source: Scopus
Source ID: 84864951116

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

Diffusion on aluminum-cluster surfaces and the cluster growth

Diffusion of adatoms have been studied on fcc polyhedral aluminum-cluster surfaces by molecular-dynamics simulations using the effective-medium theory. Diffusion of adatoms has been shown to take place by hopping along (Formula presented) facets at very low temperatures. Diffusion from one (Formula presented) facet to other (Formula presented) facets takes place at higher temperatures through a variety of mechanisms, and finally diffusion to and along (Formula presented) facets takes place at high temperatures. Diffusion from (Formula presented) to (Formula presented) facets is possible only close to the melting temperature of the cluster. The appearance of different diffusion processes as a function of temperature is in good agreement with the calculated activation energies of diffusion mechanisms along different facets and from one facet to another, including different hopping and exchange processes as well as more exotic events like the chain mechanism through a (Formula presented) facet between two (Formula presented) facets. Observed diffusion mechanisms imply that fcc clusters can grow epitaxially, having only (Formula presented) facets in accord with experimental observation. Our dynamical simulations of cluster growth support these findings.

General information

Publication status: Published
MoE publication type: Not Eligible
Organisations: Jyväskylän yliopisto
Contributors: Valkealahti, S., Manninen, M.
Number of pages: 8
Pages: 15533-15540
Publication date: 1 Jan 1998
Peer-reviewed: Yes

Publication information

Journal: Physical Review B - Condensed Matter and Materials Physics
Volume: 57
Issue number: 24
ISSN (Print): 1098-0121
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 0001165185

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

Direct measurement of vapour-metal shifts in photo- and Auger electron spectra of Zn and Cd

Photo- and Auger electron spectra have been measured simultaneously from vapour and solid metal for both zinc and cadmium by using Al K alpha X-ray excitation. The differences in the shifts of Auger and photoelectron spectra have been determined with essentially improved experimental accuracy from directly observed vapour-metal shifts.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: University of Oulu
Contributors: Kumpula, R., Vayrynen, J., Rantala, T., Aksela, S.
Publication date: 1979
Peer-reviewed: Yes

Publication information

Journal: Journal of physics c-Solid state physics
Volume: 12
Issue number: 21
Article number: 001
ISSN (Print): 0022-3719
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 25744469528

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 2.02 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

Dynamics of photovoltaic-generator-interfacing voltage-controlled buck power stage

This paper investigates the dynamic properties of the photovoltaic-generator-interfacing voltage-controlled buck power stage operating in both the maximum and limited power point tracking modes. The photovoltaic generator (PVG) is known to possess both current- and voltage-source properties with respect to its maximum power point. While voltage-fed operation is conventional, current-fed action is nontrivial and is thoroughly analyzed in this paper. The photovoltaic-generator-interfacing converter is formed by adding a capacitor at conventional voltage-fed converter input terminals, turning it into a current-fed power stage. During the maximum power point tracking phase, converter input voltage is regulated, possessing nontrivial dynamics. The situation is burdened further when output-voltage control should be alternatively realized to limit the voltage of the converter terminating the energy storage element. It is shown that both the photovoltaic generator and the terminating energy storage greatly affect the combined system dynamics. Parallel as well as cascaded control arrangements are proposed to support dual-mode system operation. Extended experimental results are shown to enforce presented theory and reveal nontrivial dynamics-related issues.

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 RandD Laboratory, Ariel University, ABB Oy, Drives
Contributors: Sitbon, M., Leppäaho, J., Suntio, T., Kuperman, A.
Number of pages: 8
Pages: 633-640
Publication date: 1 Mar 2015
Peer-reviewed: Yes

Publication information

Journal: IEEE Journal of Photovoltaics
Volume: 5
Issue number: 2
ISSN (Print): 2156-3381
Ratings: 
  • Scopus rating (2015): CiteScore 4.42 SJR 1.865 SNIP 1.929
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Keywords: Current-fed buck converter, dynamics, photovoltaic generator (PVG)

Bibliographical note

EXT="Leppäaho, J."

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 3.3 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

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

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 4.48 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

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 3.4 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

Effect of sol-gel derived in situ silica on the morphology and mechanical behavior of natural rubber and acrylonitrile butadiene rubber blends

Silica particles were generated and grown in situ by sol-gel method into rubber blends comprised of natural rubber (NR) and acrylonitrile butadiene rubber (NBR) at various blend ratios. Silica formed into rubber matrix was amorphous in nature. Amount of in situ silica increased with increase in natural rubber proportion in the blends during the sol-gel process. Morphology studies showed that the generated in situ silica were nanoparticles of different shapes and sizes mostly grown into the NR phase of the blends. In situ silica filled NR/NBR blend composites showed improvement in the mechanical and dynamic mechanical behaviors in comparison to those of the unfilled and externally filled NR/ NBR blend composites. For the NR/NBR blend at 40/60 composition, in particular, the improvement was appreciable where size and dispersion of the silica particles into the rubber matrix were found to be more uniform. Dynamic mechanical analysis revealed a strong rubber-in situ silica interaction as indicated by a positive shift of the glass transition temperature of both the rubber phases in the blends.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Engineering materials science and solutions (EMASS), Visvesvaraya National Institute of Technology, Leibniz-Institut für Polymerforschung Dresden E.V.
Contributors: Kapgate, B. P., Das, C., Das, A., Basu, D., Reuter, U., Heinrich, G.
Number of pages: 9
Pages: 501-509
Publication date: Sep 2012
Peer-reviewed: Yes

Publication information

Journal: JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY
Volume: 63
Issue number: 3
ISSN (Print): 0928-0707
Ratings: 
  • Scopus rating (2012): CiteScore 1.82 SJR 0.732 SNIP 1.133
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, Sol-gel
Source: Scopus
Source ID: 84875426374

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 2.42 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

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 2.23 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

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 2.23 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

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 1.73 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

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 6.12 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

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 3.37 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

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

Electro-optic steering of nematicons

We study the angular steering of spatial solitons in nematic liquid crystals, i.e. nematicons, exploiting their electro-optic response. Approaches to electro-optic steering include acting on the optic axis and walk-off, propagating the soliton through a voltage-adjusted refractive interface or getting it totally internally reflected. Using comb electrodes in a planar cell, maximum angular deflections of 70° are expected with the standard nematic liquid crystal mixture E7.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Frontier Photonics, Nonlinear Optics and OptoElectronics Lab, University “Roma Tre”
Contributors: Assanto, G., Piccardi, A., Barboza, R., Alberucci, A.
Number of pages: 3
Pages: 2-4
Publication date: 2012
Peer-reviewed: Yes

Publication information

Journal: Photonics Letters of Poland
Volume: 4
Issue number: 1
Ratings: 
  • Scopus rating (2012): CiteScore 1.1 SJR 0.328 SNIP 0.581
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials
Source: Scopus
Source ID: 84859416329

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 0.52 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

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 4.68 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
Source: Scopus
Source ID: 84939825598

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

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

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 1.49 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

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

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 2.85 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

Evaluation of crushing strength of spray-dried MgAl2O4 granule beds

The crushing strengths of four different experimental magnesium aluminate spinel (MgAl2O4) granule beds were monitored with the axial die pressing test after heat treatments. Precursor, magnesium hydroxide (Mg(OH)2) and magnesium oxide (MgO) as Mg precursor and aluminium oxide hydroxide Al(O)OH and α-Al2O3 as Al precursor, were used for experimental granules, which were manufactured via a dispersion manufacturing and spray-drying process. After spray-drying, granules were heat treated in air at 1000, 1100, 1200, 1300 and 1400 °C. In order to understand the potential effect of precursor, phase structure, morphology, particle size distribution and density of granules on crushing strength behaviour, scanning X-ray diffraction (XRD) was used together with electron microscopy (SEM) and laser diffraction (LDPA) for characterisation. All precursor mixtures formed spherical granules during the spray-drying process and pure spinel phase structure during heat treatment. The crushing strength test results indicated that the Al precursor clearly affected the crushing strength behaviour of experimental granule beds. The highest strength was observed for granule beds with Al(O)OH) as Al and Mg(OH)2 as Mg precursor.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Materials Science, Engineering materials science and solutions (EMASS), VTT Technical Research Centre of Finland
Contributors: Kanerva, U., Suhonen, T., Lagerbom, J., Levänen, E.
Number of pages: 7
Pages: 8494-8500
Publication date: 1 Aug 2015
Peer-reviewed: Yes

Publication information

Journal: Ceramics International
Volume: 41
Issue number: 7
ISSN (Print): 0272-8842
Ratings: 
  • Scopus rating (2015): CiteScore 2.64 SJR 0.823 SNIP 1.353
Original language: English
ASJC Scopus subject areas: Ceramics and Composites, Process Chemistry and Technology, Electronic, Optical and Magnetic Materials, Surfaces, Coatings and Films, Materials Chemistry
Keywords: Axial pressing, Granule, MgAl<inf>2</inf>O<inf>4</inf> spinel, The crushing strength

Bibliographical note

EXT="Lagerbom, Juha"
EXT="Kanerva, Ulla"

Source: Scopus
Source ID: 84929271760

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

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

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

General information

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

Publication information

Journal: Semiconductor Science and Technology
Volume: 33
Issue number: 8
Article number: 084002
ISSN (Print): 0268-1242
Ratings: 
  • Scopus rating (2018): CiteScore 2.4 SJR 0.744 SNIP 1.014
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

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): 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

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

Fabrication of ssDNA/Oligo(ethylene glycol) monolayers and patterns by exchange reaction promoted by ultraviolet light irradiation

Using a representative test system, we present here a versatile approach to prepare mixed monolayers of thiolated single-stranded DNA (ssDNA) and oligo(ethylene glycol) substituted alkanethiols (OEG-AT) in a broad range of compositions as well as ssDNA/OEG-AT patterns of desired shape imbedded into a biorepulsive background. The procedure involves two steps. First, a primary, well-defined OEG-AT monolayer on a solid support is exposed to UV light in either homogeneous or lithographic fashion. Second, the exchange reaction between the damaged OEG-AT species in the film and ssDNA substituents in solution occurs, resulting in formation of ssDNA/OEG-AT monolayer or pattern. The above procedure relies on commercially available compounds and does not require vacuum, which simplifies its application in research and industrial laboratories. The composition of the mixed films or ssDNA/OEG-AT spots (lithography) can be precisely adjusted by UV dose in an almost entire composition range. It was demonstrated that the procedure can be performed with UV light of different wavelengths (254 or 365 nm), which opens new possibilities for lithography. Using advanced spectroscopic tools, it was shown that ssDNA molecules imbedded into the OEG-AT matrix maintain their identity and intact character as well as exhibit predominant upright orientation typical of one-component films of thiolated ssDNA. The OEG-AT constituents of the mixed monolayers were found to be intact as well, with all UV damaged OEG-AT species being exchanged for ssDNA. Finally, a representative ssDNA/OEG-AT pattern was fabricated.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Integrated Technologies for Tissue Engineering Research (ITTE), Universitat Heidelberg
Contributors: Khan, M. N., Zharnikov, M.
Number of pages: 11
Pages: 24883-24893
Publication date: 27 Nov 2013
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry C
Volume: 117
Issue number: 47
ISSN (Print): 1932-7447
Ratings: 
  • Scopus rating (2013): CiteScore 5.14 SJR 2.143 SNIP 1.432
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: 84889582340

Research output: Contribution to journalArticleScientificpeer-review

Fabrication of ssDNA/oligo(ethylene glycol) monolayers by promoted exchange reaction with thiol and disulfide substituents

Biorepulsive oligo(ethylene glycol)-substituted alkanethiolate (OEG-AT) monolayers on gold can serve as primary templates for promoted (by electron irradiation) exchange reaction with thiolated ssDNA species, resulting in the formation of mixed OEG-AT/ssDNA monolayers of desired composition. Here we test the ability of alternative, disulfide precursors to serve as substituents in such a reaction. Two representative molecules, based on adenine-based homo-oligonucleotide (25-mer), were used, viz., asymmetric disulfide with a short second chain (A25SSOH) and symmetric disulfide (A25SSA25). The results were compared to the reference system of thiolated ssDNA (A25SH). Both disulfide precursors were found to be suitable for the reaction, further extending the types of commercially available compounds which can be used for this approach. A25SSOH exhibited quite high efficiency, similar to A25SH, while the efficiency of A25SSA25 was noticeably lower, especially at low irradiation doses (2). Also, the single component, A25SSA25-based ssDNA monolayer, was of lower quality as compared to the films prepared from the A25SH and A25SSOH precursors. The above observations were explained by the bulky character and conformational flexibility of A25SSA25, which hinder the proper assembly and efficient exchange reaction.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Integrated Technologies for Tissue Engineering Research (ITTE), Universitat Heidelberg
Contributors: Khan, M. N., Zharnikov, M.
Number of pages: 9
Pages: 3093-3101
Publication date: 13 Feb 2014
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry C
Volume: 118
Issue number: 6
ISSN (Print): 1932-7447
Ratings: 
  • Scopus rating (2014): CiteScore 5.08 SJR 2.032 SNIP 1.434
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: 84894037828

Research output: Contribution to journalArticleScientificpeer-review

FEM for directly coupled magneto-mechanical phenomena in electrical machines

A directly coupled magneto-mechanical model is proposed for simulating the effect of the magnetostriction and electromagnetic stress in iron. The model is based on the general balance laws of electromagnetism, mechanics, and continuum thermodynamics. It is implemented in 2-D by using a conforming finite element method for the magnetic vector potential and the displacement field. The method is applied to two different types of induction machines.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Aalto University
Contributors: Fonteyn, K., Belahcen, A., Kouhia, R., Rasilo, P., Arkkio, A.
Number of pages: 4
Pages: 2923-2926
Publication date: Aug 2010
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Magnetics
Volume: 46
Issue number: 8
ISSN (Print): 0018-9464
Ratings: 
  • Scopus rating (2010): SJR 0.712 SNIP 1.134
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Keywords: electromagnetic stress tensor, finite element analysis, Magneto-mechanical coupling, magnetostriction
Source: Scopus
Source ID: 77954840624

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

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): 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

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

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

General information

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

Publication information

Journal: Journal of Colloid and Interface Science
Volume: 522
ISSN (Print): 0021-9797
Ratings: 
  • Scopus rating (2018): CiteScore 5.93 SJR 1.29 SNIP 1.342
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

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 5.67 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

Frequency modulation of semiconductor disk laser pulses

A numerical model is constructed for a semiconductor disk laser mode-locked by a semiconductor saturable absorber mirror (SESAM), and the effect that the phase modulation caused by gain and absorption saturation in the semiconductor has on pulse generation is examined. The results demonstrate that, in a laser cavity with sufficient second-order dispersion, alternating-sign frequency modulation of pulses can be compensated for. We also examine a model for tuning the dispersion in the cavity of a disk laser using a Gires - Tournois interferometer with limited thirdorder dispersion.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Optoelectronics Research Centre, Research group: Ultrafast and intense lasers, Ulyanovsk State University
Contributors: Zolotovskii, I. O., Korobko, D. A., Okhotnikov, O. G.
Number of pages: 7
Pages: 628-634
Publication date: 2015
Peer-reviewed: Yes

Publication information

Journal: Quantum Electronics
Volume: 45
Issue number: 7
ISSN (Print): 1063-7818
Ratings: 
  • Scopus rating (2015): CiteScore 1.07 SJR 0.589 SNIP 1.177
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Statistical and Nonlinear Physics
Keywords: Frequency modulation of pulses., Semiconductor disk laser
Source: Scopus
Source ID: 84938310088

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

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

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): 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

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

Generation of a broad IR spectrum and N-soliton compression in a longitudinally inhomogeneous dispersion-shifted fibre

The propagation of N-soliton pulses in an optical fibre with slowly decreasing, shifted anomalous dispersion has been studied experimentally and theoretically. Using a generalised nonlinear Schrodinger equation, we have constructed an adequate numerical model for light propagation in such fibre. Using numerical simulation, we have shown that the use of dispersion-decreasing fibres ensures higher average dispersive radiation intensity and better uniformity of the supercontinuum spectrum. A reduction in the third-order dispersion of such fibres enables supercontinuum generation with a bandwidth exceeding that in homogeneous fibres by several hundred nanometres even in the case of a medium-power subpicosecond source.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Optoelectronics Research Centre, Research group: Ultrafast and intense lasers, Ulyanovsk State University, Optoelectronics Research Centre, Tampere University of Technology, A. M. Prokhorov General Physics Institute, Russian Academy of Sciences
Contributors: Zolotovskii, I. O., Korobko, D. A., Okhotnikov, O. G., Stolyarov, D. A., Sysolyatin, A. A.
Number of pages: 9
Pages: 844-852
Publication date: 2015
Peer-reviewed: Yes

Publication information

Journal: Quantum Electronics
Volume: 45
Issue number: 9
ISSN (Print): 1063-7818
Ratings: 
  • Scopus rating (2015): CiteScore 1.07 SJR 0.589 SNIP 1.177
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Statistical and Nonlinear Physics
Keywords: Dispersion-shifted fibres, Generation of a broad spectrum, Longitudinally inhomogeneous optical fibres.
Source: Scopus
Source ID: 84943269989

Research output: Contribution to journalArticleScientificpeer-review

Generation of bound states of pulses in a soliton laser with complex relaxation of a saturable absorber

A numerical model of a soliton fibre laser with a semiconductor saturable absorber mirror (SESAM), characterised by the complex dynamics of absorption relaxation, is considered. It is shown that stationary bound states of pulses can be formed in this laser as a result of their interaction via the dispersion-wave field. The stability of stationary bound states of several pulses is analysed. It is shown that an increase in the number of pulses in a stationary bound state leads eventually to its decay and formation of a random bunch. It is found that the bunch stability is caused by the manifestation of nonlinear self-phase modulation, which attracts pulses to the bunch centre. The simulation results are in qualitative agreement with experimental data.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Optoelectronics Research Centre, Research group: Ultrafast and intense lasers, Frontier Photonics, Ulyanovsk State University
Contributors: Zolotovskii, I. O., Korobko, D. A., Gumenyuk, R. V., Okhotnikov, O. G.
Number of pages: 9
Pages: 26-34
Publication date: 2015
Peer-reviewed: Yes

Publication information

Journal: Quantum Electronics
Volume: 45
Issue number: 1
ISSN (Print): 1063-7818
Ratings: 
  • Scopus rating (2015): CiteScore 1.07 SJR 0.589 SNIP 1.177
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials, Atomic and Molecular Physics, and Optics, Statistical and Nonlinear Physics
Keywords: soliton fibre laser, semiconductor saturable absorber mirror, bound states of pulses, FIBER LASER, MODE-LOCKING, OPTICAL-FIBERS, DISPERSION, RECOVERY, GAIN, TECHNOLOGY, ABSORPTION, MIRRORS, SLOW
Source: WOS
Source ID: 000349382000006

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

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 4.58 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

Geometry Analysis in Screen-Printed Stretchable Interconnects

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

General information

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

Publication information

Journal: IEEE Transactions on Components, Packaging and Manufacturing Technology
Volume: 8
Issue number: 8
ISSN (Print): 2156-3950
Ratings: 
  • Scopus rating (2018): CiteScore 2.26 SJR 0.552 SNIP 1.269
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

Germanium-on-glass solar cells: Fabrication and characterization

We report on Germanium on Glass solar cells realized by wafer bonding, layer splitting and epitaxial regrowth. We provide a detailed description of the layer transfer process and discuss the material characterization. The solar cells are fabricated and tested to extract the most significant figures of merit, evaluating their performance versus device area and operating temperature. The cells exhibit typical conversion efficiencies exceeding 2.4% under AM1.5 irradiation and a maximum efficiency of 3.7% under concentrated excitation. This Germanium on Glass approach is promising in terms of added flexibility in multi-junction engineering and allows a significant cost reduction thanks to the re-usability of the Ge substrates.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Frontier Photonics, University “Roma Tre”, Circadian Solar, Nonlinear Optics and OptoElectronics Lab
Contributors: Sorianello, V., Colace, L., Maragliano, C., Fulgoni, D., Nash, L., Assanto, G.
Number of pages: 13
Pages: 216-228
Publication date: 2013
Peer-reviewed: Yes

Publication information

Journal: Optical Materials Express
Volume: 3
Issue number: 2
ISSN (Print): 2159-3930
Ratings: 
  • Scopus rating (2013): CiteScore 3.42 SJR 1.757 SNIP 2.34
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials
Source: Scopus
Source ID: 84874144417

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 21.32 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

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

Graphene-based tunable plasmon induced transparency in gold strips

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

General information

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

Publication information

Journal: Optical Materials Express
Volume: 8
Issue number: 4
ISSN (Print): 2159-3930
Ratings: 
  • Scopus rating (2018): CiteScore 2.76 SJR 0.886 SNIP 1.045
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

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

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

Halogen bonding versus hydrogen bonding in driving self-assembly and performance of light-responsive supramolecular polymers

Halogen bonding is arguably the least exploited among the many non-covalent interactions used in dictating molecular self-assembly. However, its directionality renders it unique compared to ubiquitous hydrogen bonding. Here, the role of this directionality in controlling the performance of light-responsive supramolecular polymers is highlighted. In particular, it is shown that light-induced surface patterning, a unique phenomenon occurring in azobenzene-containing polymers, is more efficient in halogen-bonded polymer-azobenzene complexes than in the analogous hydrogen-bonded complexes. A systematic study is performed on a series of azo dyes containing different halogen or hydrogen bonding donor moieties, complexed to poly(4-vinylpyridine) backbone. Through single-atom substitution of the bond-donor, control of both the strength and the nature of the noncovalent interaction between the azobenzene units and the polymer backbone is achieved. Importantly, such substitution does not significantly alter the electronic properties of the azobenzene units, hence providing us with unique tools in studying the structure-performance relationships in the light-induced surface deformation process. The results represent the first demonstration of light-responsive halogen-bonded polymer systems and also highlight the remarkable potential of halogen bonding in fundamental studies of photoresponsive azobenzene-containing polymers.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Frontier Photonics, Tokyo Institute of Technology, Politecnico di Milano, Università degli Studi di Milano, Aalto University, VTT Technical Research Centre of Finland
Contributors: Priimagi, A., Cavallo, G., Forni, A., Gorynsztejn-Leben, M., Kaivola, M., Metrangolo, P., Milani, R., Shishido, A., Pilati, T., Resnati, G., Terraneo, G.
Number of pages: 8
Pages: 2572-2579
Publication date: 20 Jun 2012
Peer-reviewed: Yes

Publication information

Journal: Advanced Functional Materials
Volume: 22
Issue number: 12
ISSN (Print): 1616-301X
Ratings: 
  • Scopus rating (2012): CiteScore 10.41 SJR 5.689 SNIP 2.624
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Biomaterials, Condensed Matter Physics, Electrochemistry
Keywords: halogen bonding, optically active materials, self-assembly, supramolecular polymers, surface relief gratings
Source: Scopus
Source ID: 84862000539

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

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

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): 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

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

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 1.86 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

Hot spot temperature in an HTS Coil: Simulations with MIITs and finite element method

MIITs, a zero-dimensional concept to study hot spot temperature, has been previously used to estimate hot spot temperatures and quench heater delays in NbTi and Nb3Sn magnets. However, quench behavior is completely different in high-temperature superconducting (HTS) magnets due to the slow normal zone propagation velocity and the high temperature margin. Because the MIITs concept does not take into account thermal diffusion in the magnet, opposite to the finite-element method (FEM) analysis, the difference of these concepts is studied in this paper. Here, we have taken the approach to compute the hot spot temperatures for a future HTS magnet, designed to be built from REBCO Roebel cable, with MIITs and FEM simulations. The magnet protection is accomplished with a dump resistor, and the effect of quench detection threshold voltage on the hot spot temperature has been studied. Furthermore, the inductance of the magnet increases with the magnet length. Thus, there exists a maximum inductance of the magnet, which should not be exceeded to be able to protect the magnet only with a dump resistor. The hot spot temperatures with different values of inductance are also studied in this paper. Our simulations show that the hot spot temperatures computed with MIITs are from 60 to 150 K higher than those of FEM analysis. Thus, the MIITs concept seems unreliable when considering hot spot temperatures in HTS magnets protected with only dump resistors. However, the MIITs concept might be a usable tool when comparing different magnet designs. If 400 K is the upper limit for the hot spot temperature and the protection scheme includes only a dump resistor, the length of the investigated magnet can be increased to only such value that the magnet inductance is at most 50 mH.

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
Contributors: Härö, E., Stenvall, A., Van Nugteren, J., Kirby, G.
Publication date: 1 Apr 2015
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Applied Superconductivity
Volume: 25
Issue number: 2
ISSN (Print): 1051-8223
Ratings: 
  • Scopus rating (2015): CiteScore 1.27 SJR 0.403 SNIP 1.046
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Condensed Matter Physics, Electronic, Optical and Magnetic Materials
Keywords: Finite element method (FEM), high-temperature superconductors (HTSs), quench simulation, stability analysis, superconducting magnets
Source: Scopus
Source ID: 84926385685

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): 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

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

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

Identification of synchronous machine magnetization characteristics from calorimetric core-loss and no-load curve measurements

The magnetic material characteristics of a wound-field synchronous machine are identified based on global calorimetric core-loss and no-load curve measurements. This is accomplished by solving a coupled experimental-numerical electromagnetic inverse problem, formulated to minimize the difference between a finite-element (FE) simulation-based Kriging surrogate model and the measurement results. The core-loss estimation in the FE model is based on combining a dynamic iron-loss model and a static vector Jiles-Atherton hysteresis model, whose parameters that are obtained by solving the inverse problem. The results show that reasonable hysteresis loops can be produced for a grid-supplied machine, while for an inverter-supplied machine the limitations in the FE and iron-loss models seemingly exaggerate the area of the loop. In addition, the effect of the measurement uncertainty on the inverse problem is quantitatively estimated.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Smart Energy Systems (SES), Universiteit Gent, Ghent University, Zwijnaarde, Belgium, Cairo University, Aalto University
Contributors: Rasilo, P., Abdallh, A. A. E., Belahcen, A., Arkkio, A., Dupré, L.
Publication date: 1 Mar 2015
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Magnetics
Volume: 51
Issue number: 3
Article number: 2001304
ISSN (Print): 0018-9464
Ratings: 
  • Scopus rating (2015): CiteScore 1.77 SJR 0.575 SNIP 1.189
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Keywords: Calorimetric loss measurements, electromagnetic inverse problems, iron losses, magnetic hysteresis, synchronous machines
Source: Scopus
Source ID: 84928780507

Research output: Contribution to journalArticleScientificpeer-review

Importance of iron-loss modeling in simulation of wound-field synchronous machines

Effect of hysteresis, eddy-current and excess-loss modeling on the 2-D field solution of 12.5-MW and 150-kVA wound-field synchronous machines is studied. The study is performed by comparing the differences in the solutions obtained with three different finite element formulations: one with iron losses fully included, one using only single-valued material properties, and one completely neglecting the iron losses from the solution. The electrical operating points, i.e., the terminal currents and powers are found to be only little influenced by the iron-loss model. However, the rotor eddy-current losses are found to be overestimated, if the skin effect of the eddy currents is uncoupled from the solution. Using single-valued material properties instead of hysteretic ones has a smaller effect on the rotor side, but increases the hysteresis losses in the stator. The effects on the total core losses thus depend on their distribution between the stator and the rotor. It is concluded that using single-valued material properties is reasonable in order to improve the computational performance despite the slight overestimation in the computed core losses. However, for accurate modeling of the rotor losses, the skin effect of the eddy currents should be included in the solution.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Smart Energy Systems (SES), Aalto University
Contributors: Rasilo, P., Belahcen, A., Arkkio, A.
Number of pages: 10
Pages: 2495-2504
Publication date: 2012
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Magnetics
Volume: 48
Issue number: 9
ISSN (Print): 0018-9464
Ratings: 
  • Scopus rating (2012): CiteScore 1.89 SJR 0.769 SNIP 1.55
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Keywords: Eddy currents, ferromagnetic materials, finite element methods, magnetic hysteresis, synchronous machines
Source: Scopus
Source ID: 84865464767

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

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

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 0.83 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

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

Influence of the P2O5/Al2O3 co-doping on the local environment of erbium ions and on the 1.5 μm quantum efficiency of Er3+-borosilicate glasses

In this paper, the absorption properties of Er3+-doped borosilicate glasses with various P2O5 and Al 2O3 content are measured for different silica concentrations. The Judd-Ofelt parameters (Ω2, Ω4 and Ω6) have been calculated in order to investigate the local environment of the rare-earth cations. The compositional changes of Ω2 and Ω6 are attributed to changes in the bonding between Er3+ and surrounding ligand groups due to structural modifications occurring with the introduction of P2O 5 and Al2O3. The luminescence quantum efficiency of the 4I13/24I 15/2 transition slightly increases with the addition of P 2O5 whereas it decreases with the progressive replacement of P2O5 by Al2O3. We noticed that it also increases when the silica content is higher.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Frontier Photonics, Politecnico di Torino, nLIGHT Corporation, Johan Gadolin Process Chemistry Centre, Abo Akademi University
Contributors: Bourhis, K., Boetti, N. G., Koponen, J., Milanese, D., Petit, L.
Number of pages: 6
Pages: 926-931
Publication date: Mar 2014
Peer-reviewed: Yes

Publication information

Journal: Optical Materials
Volume: 36
Issue number: 5
ISSN (Print): 0925-3467
Ratings: 
  • Scopus rating (2014): CiteScore 2.24 SJR 0.721 SNIP 1.204
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: Er doped borosilicate glasses, Judd-Ofelt parameters, Lifetime, Luminescence quantum efficiency
Source: Scopus
Source ID: 84893847084

Research output: Contribution to journalArticleScientificpeer-review

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

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

General information

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

Publication information

Journal: Ceramics International
Volume: 44
Issue number: 10
ISSN (Print): 0272-8842
Ratings: 
  • Scopus rating (2018): CiteScore 3.5 SJR 0.888 SNIP 1.297
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

Inkjet catalyst printing and electroless copper deposition for low-cost patterned microwave passive devices on paper

A scalable, low-cost process for fabricating copper-based microwave components on flexible, paper-based substrates is demonstrated. An inkjet printer is used to deposit a catalyst-bearing solution (tailored for such printing) in a desired pattern on commercially-available, recyclable, non-toxic (Teslin®) paper. The catalystbearing paper is then immersed in an aqueous copper-bearing solution to allow for electroless deposition of a compact and conformal layer of copper in the inkjet-derived pattern. Meander monopole antennas comprised of such electroless-deposited copper patterns on paper exhibited comparable performance as for antennas synthesized via inkjet printing of a commercially-available silver nanoparticle ink. However, the solution-based patterning and electroless copper deposition process avoids nozzle-clogging problems and costs associated with noble metal particle-based inks. This process yields compact conductive copper layers without appreciable oxidation and without the need for an elevated temperature, post-deposition thermal treatment commonly required for noble metal particle-based ink processes. This low-cost copper patterning process is readily scalable on virtually any substrate and may be used to generate a variety of copper-based microwave devices on flexible, paper-based substrates.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Sensing Systems for Wireless Medicine (MediSense), Georgia Institute of Technology, School of Electrical and Computer Engineering, Georgia Institute of Technology
Contributors: Cook, B. S., Fang, Y., Kim, S., Le, T., Goodwin, W. B., Sandhage, K. H., Tentzeris, M. M.
Number of pages: 8
Pages: 669-676
Publication date: Sep 2013
Peer-reviewed: Yes

Publication information

Journal: Electronic Materials Letters
Volume: 9
Issue number: 5
ISSN (Print): 1738-8090
Ratings: 
  • Scopus rating (2013): CiteScore 3.39 SJR 1.219 SNIP 2.498
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials
Keywords: antennas, copper metallization, flexible and recyclable substrates, inkjet printed electronics, paper-bearing electronics, RF devices
Source: Scopus
Source ID: 84883808468

Research output: Contribution to journalArticleScientificpeer-review

Inkjet printing of radio frequency electronics: Design methodologies and application of novel nanotechnologies

We discuss here the use of inkjet printing technology as an attractive alternative for the fabrication of radio frequency (RF) electronics. Inkjet printing is compared to widelyused traditional methods such as wet etching and mechanical milling with discussion of the advantages and potential disadvantages afforded by the technology. Next the paper presents the current state of the art for RF printed electronics, including fundamental fabrication technologies, methodologies, and materials. Included are detailed discussions of the fabrication of foundational conductive elements, integration of external elements via low temperature bonding techniques, and enhancement strategies focusing on the addition of novel materials. We then present some current challenges related to inkjet printing, along with some exciting recent advances in materials technology seeking to overcome the current limitations and to expand the frontier of the technology. Following are multiple examples detailing the successful use of inkjet printing methods in the creation of novel RF devices, providing proof of concept and illustrating in greater detail the concepts presented in the theoretical sections.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Sensing Systems for Wireless Medicine (MediSense), Georgia Institute of Technology, School of Electrical and Computer Engineering
Contributors: Le, T., Lin, Z., Vyas, R., Lakafosis, V., Yang, L., Traille, A., Tentzeris, M. M., Wong, C. P.
Publication date: 2013
Peer-reviewed: Yes

Publication information

Journal: Journal of Electronic Packaging
Volume: 135
Issue number: 1
Article number: 011007
ISSN (Print): 1043-7398
Ratings: 
  • Scopus rating (2013): CiteScore 0.94 SJR 0.43 SNIP 0.804
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Mechanics of Materials, Computer Science Applications, Electrical and Electronic Engineering
Keywords: Annealing, CNT, Conductive silver ink, Direct write, Electrical design, Flexible circuits, Graphene, Inkjet-printed electronics, Low temperature bonding, Microwave, Organic electronics, Paper-based electronics, Sensors, SOP
Source: Scopus
Source ID: 84878547011

Research output: Contribution to journalArticleScientificpeer-review

Instability of cuboctahedral copper clusters

Equilibrium structures of copper clusters up to 10 000 atoms are studied using molecular-dynamics and effective-medium theory. Icosahedral closed-shell clusters are most stable up to 2500 atoms and the Wulff polyhedra are favored for larger clusters. Cuboctahedral closed-shell clusters up to 2000 atoms are unstable. They undergo a nondiffusive transition to an icosahedral structure at low temperatures and melt directly above the fcc-cluster-melting temperature. The melting temperature decreases with decreasing cluster size but not as deeply as has been reported for pure metals.

General information

Publication status: Published
MoE publication type: Not Eligible
Organisations: Jyväskylän yliopisto
Contributors: Valkealahti, S., Manninen, M.
Number of pages: 4
Pages: 9459-9462
Publication date: 1 Jan 1992
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 45
Issue number: 16
ISSN (Print): 0163-1829
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 0000550996

Research output: Contribution to journalArticleScientificpeer-review

Interfacial design and structure of protein/polymer films on oxidized AlGaN surfaces

Protein detection using biologically or immunologically modified field-effect transistors (bio/immunoFETs) depends on the nanoscale structure of the polymer/protein film at sensor interfaces (Bhushan 2010 Springer Handbook of Nanotechnology 3rd edn (Heidelberg: Springer); Gupta et al 2010 The effect of interface modification on bioFET sensitivity, submitted). AlGaN-based HFETs (heterojunction FETs) are attractive platforms for many protein sensing applications due to their electrical stability in high osmolarity aqueous environments and favourable current drive capabilities. However, interfacial polymer/protein films on AlGaN, though critical to HFET protein sensor function, have not yet been fully characterized. These interfacial films are typically comprised of protein-polymer films, in which analyte-specific receptors are tethered to the sensing surface with a heterobifunctional linker molecule (often a silane molecule). Here we provide insight into the structure and tribology of silane interfaces composed of one of two different silane monomers deposited on oxidized AlGaN, and other metal oxide surfaces. We demonstrate distinct morphologies and wear properties for the interfacial films, attributable to the specific chemistries of the silane monomers used in the films. For each specific silane monomer, film morphologies and wear are broadly consistent on multiple oxide surfaces. Differences in interfacial film morphology also drive improvements in sensitivity of the underlying HFET (coincident with, though not necessarily caused by, differences in interfacial film thickness). We present a testable model of the hypothetical differential interfacial depth distribution of protein analytes on FET sensor interfaces with distinct morphologies. Empirical validation of this model may rationalize the actual behaviour of planar immunoFETs, which has been shown to be contrary to expectations of bio/immunoFET behaviour prevalent in the literature for the last 20 years. Improved interfacial properties of bio/immunoHFETs have improved bio/immunoHFET performance: better understanding of interfaces may lead to mechanistic understanding of FET sensor properties and to clinical translation of the immunoFET platform.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Augmented Human Activities (AHA), Ohio State University, Department of Electrical and Computer Engineering
Contributors: Gupta, S. K., Wu, H. H., Kwak, K. J., Casal, P., Nicholson, T. R., Wen, X., Anisha, R., Bhushan, B., Berger, P. R., Lu, W., Brillson, L. J., Lee, S. C.
Publication date: 26 Jan 2011
Peer-reviewed: Yes

Publication information

Journal: Journal of Physics D: Applied Physics
Volume: 44
Issue number: 3
Article number: 34010
ISSN (Print): 0022-3727
Ratings: 
  • Scopus rating (2011): CiteScore 2.36 SJR 1.266 SNIP 1.424
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Electronic, Optical and Magnetic Materials, Acoustics and Ultrasonics, Surfaces, Coatings and Films
Source: Scopus
Source ID: 78650639127

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 2.38 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

Investigating the metallic behavior of Na clusters using site-specific polarizabilities

A site-specific analysis scheme based on density functional theory is used to investigate the static polarizability response of NaN clusters for N up to 80. The cluster structures used in the study stem from extensive searches for the respective global minima. The analysis involves partitioning the total cluster polarizability exactly into site (or atomic) contributions; it also results in the decomposition of the polarizability into local (or dipole) and charge transfer contributions. The computed total polarizabilities are found to be in excellent agreement with recent experimental measurements up to a small overall shift. The site analysis provides clear evidence that interior atoms in sodium clusters are strongly screened from an applied external field by the charge induced at the cluster surface. In addition, cluster size trends in the local and charge transfer contributions are shown to be reproduced very well by a simple metal sphere model. The overall picture is that of clusters exhibiting metallic behavior down to the smallest sizes.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Computational Science X (CompX), Northwest University China, Central Michigan University, Argonne National Laboratory
Contributors: Ma, L., Jackson, K. A., Wang, J., Horoi, M., Jellinek, J.
Publication date: 24 Jan 2014
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 89
Issue number: 3
Article number: 035429
ISSN (Print): 1098-0121
Ratings: 
  • Scopus rating (2014): CiteScore 3.3 SJR 2.762 SNIP 1.316
Original language: English
ASJC Scopus subject areas: Condensed Matter Physics, Electronic, Optical and Magnetic Materials
Source: Scopus
Source ID: 84894580248

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 1.91 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

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

Iron losses, magnetoelasticity and magnetostriction in ferromagnetic steel laminations

The interdependence of iron losses and magnetoelasticity in ferromagnetic laminations is studied by numerical simulations. For the simulations, a finite-element model for the eddy currents in the lamination is coupled to a constitutive magnetomechanical material law. We demonstrate how the experimentally apparent rate-dependency of magnetostriction partly results from the comparison of the local surface magnetostriction to the average flux density supplied through the sheet. The average flux density is a global quantity and lags behind the local surface magnetostriction due to the skin effect of the eddy currents. Accurate modeling of the skin effect also shows that in addition to the hysteresis losses, the eddy-current losses also change as a result of applied mechanical stress, contrary to some earlier discussions in the literature.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Smart Energy Systems (SES), Aalto University
Contributors: Rasilo, P., Singh, D., Belahcen, A., Arkkio, A.
Number of pages: 4
Pages: 2041-2044
Publication date: 2013
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Magnetics
Volume: 49
Issue number: 5
ISSN (Print): 0018-9464
Ratings: 
  • Scopus rating (2013): CiteScore 1.75 SJR 0.587 SNIP 1.395
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Keywords: Magnetic losses, magnetic materials, magnetomechanical effects, magnetostriction
Source: Scopus
Source ID: 84877841540

Research output: Contribution to journalArticleScientificpeer-review

Irradiation promoted exchange reaction with disulfide substituents

Exchange reaction between the primary self-assembled monolayer (SAM) on gold and potential molecular substituents capable of forming a SAM on the same substrate can be promoted by electron irradiation. Here we demonstrate that such a promoted reaction can be performed not only with thiols but with disulfides as substituents as well. This extends significantly the assortments of the suitable compounds, resulting in a broader variety of mixed SAMs and chemical patterns which can be fabricated by this technique. The kinetics of the promoted exchange reaction was studied in detail. The feasibility and practical usefulness of the approach were demonstrated by the experiments with a disulfide substituent bearing a tail group which can serve as an initiator for surface-initiated polymerization. A variety of complex polymer brush patterns was prepared using several representative polymers, relevant for biomedical research and applications, as test systems.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Integrated Technologies for Tissue Engineering Research (ITTE), Universitat Heidelberg
Contributors: Khan, M. N., Zharnikov, M.
Number of pages: 10
Pages: 14534-14543
Publication date: 18 Jul 2013
Peer-reviewed: Yes

Publication information

Journal: Journal of Physical Chemistry C
Volume: 117
Issue number: 28
ISSN (Print): 1932-7447
Ratings: 
  • Scopus rating (2013): CiteScore 5.14 SJR 2.143 SNIP 1.432
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: 84880559790

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

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

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 0.37 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

Liquid crystal light valves: A versatile platform for nematicons

We illustrate the generation and control of optical spatial solitary waves (nematicons) in liquid crystal light valves with nematic liquid crystals and a photoconductive layer. The latter allows to all-optically varying the birefringent walk-off and the extraordinary-wave refractive index, hence, the trajectory of a nematicon propagating in the thickness of the valve.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Univ Roma Tre, Roma Tre University, Dept Elect Engn, NooEL, University “Roma Tre”, CNRS
Contributors: Assanto, G., Piccardi, A., Alberucci, A., Residori, S., Bortolozzo, U.
Number of pages: 3
Pages: 151-153
Publication date: 2009
Peer-reviewed: Yes

Publication information

Journal: Photonics Letters of Poland
Volume: 1
Issue number: 4
ISSN (Print): 2080-2242
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials
Source: Scopus
Source ID: 78650977780

Research output: Contribution to journalArticleScientificpeer-review

Localized surface plasmon resonance in silver nanoparticles: Atomistic first-principles time-dependent density-functional theory calculations

We observe using ab initio methods that localized surface plasmon resonances in icosahedral silver nanoparticles enter the asymptotic region already between diameters of 1 and 2 nm, converging close to the classical quasistatic limit around 3.4 eV. We base the observation on time-dependent density-functional theory simulations of the icosahedral silver clusters Ag55(1.06nm), Ag147(1.60nm), Ag309(2.14nm), and Ag561(2.68 nm). The simulation method combines the adiabatic GLLB-SC exchange-correlation functional with real time propagation in an atomic orbital basis set using the projector-augmented wave method. The method has been implemented for the electron structure code GPAW within the scope of this work. We obtain good agreement with experimental data and modeled results, including photoemission and plasmon resonance. Moreover, we can extrapolate the ab initio results to the classical quasistatically modeled icosahedral clusters.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Electronic Structure Theory, Research area: Computational Physics, Department of Physics, Chalmers University of Technology, COMP Centre of Excellence, Department of Applied Physics, Aalto University, University of Jyväskylä, Nano-Bio Spectroscopy Group and European Theoretical Spectroscopy Facility (ETSF), Universidad del País Vasco UPV/EHU, CSC-IT Center for Science Ltd.
Contributors: Kuisma, M., Sakko, A., Rossi, T. P., Larsen, A. H., Enkovaara, J., Lehtovaara, L., Rantala, T. T.
Number of pages: 8
Publication date: 24 Mar 2015
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 91
Issue number: 11
Article number: 115431
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
Keywords: OPTICAL-PROPERTIES, METAL NANOPARTICLES, AG-CLUSTERS, APPROXIMATION, SIZE, SPECTROSCOPY, ENVIRONMENT, NANOSHELLS, SYSTEMS, SHAPE
Source: Scopus
Source ID: 84926483236

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 4.58 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

Low-temperature germanium thin films on silicon

We discuss thermal evaporation of Germanium thin films as a suitable route to realizing near-infrared detectors integrated on a Silicon platform. We study the structural properties of samples grown at various substrate temperatures by X-ray diffraction and transmission electron microscopy, showing that Ge thin films are amorphous when deposited below 225°C, mono-crystalline between 225 and 400°C, poly-crystalline above 450°C. We further investigate their optical and electrical properties using differential optical absorption spectroscopy, Hall and photocurrent measurements. Finally, with the evaporated Ge thin films we demonstrate near-infrared photodiodes with low dark current density and good responsivity at 1.55 μm.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Frontier Photonics, Nonlinear Optics and OptoElectronics Lab, Institute IMEM-CNR
Contributors: Sorianello, V., Colace, L., Armani, N., Rossi, F., Ferrari, C., Lazzarini, L., Assanto, G.
Number of pages: 10
Pages: 856-865
Publication date: 1 Sep 2011
Peer-reviewed: Yes

Publication information

Journal: Optical Materials Express
Volume: 1
Issue number: 5
ISSN (Print): 2159-3930
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials
Source: Scopus
Source ID: 84862177957

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

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): 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

Measuring optical anisotropy in poly(3,4-ethylene dioxythiophene): poly(styrene sulfonate) films with added graphene

Abstract Graphene is a 2D nanomaterial having a great potential for applications in electronics and optoelectronics. Composites of graphene with conducting polymers have shown high performance in practical devices and their solution-processability enables low-cost and high-throughput mass manufacturing using printing techniques. Here we measure the effect of incorporation of graphene into poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) to the optical anisotropy, absorbance and conductivity of the film. Uniaxial anisotropy in PEDOT:PSS films has been thought to be caused by the spin-coating process used in fabrication. We have characterized spray- and spin-coated films using ellipsometry and total internal reflection spectroscopy, the latter especially for films too thick and uneven for ellipsometry, and show that spray-coating, similar to inkjet printing, also produces consistently anisotropic properties even in very thick and uneven films. Possible plasmonic excitations related to graphene are not seen in the films. The optical and electrical anisotropy of graphene/PEDOT:PSS enables routes to high performance devices for electronics, photonics and optoelectronics.

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, Integrated Technologies for Tissue Engineering Research (ITTE), Miktech Oy, University of Jyväskylä
Contributors: Isoniemi, T., Tuukkanen, S., Cameron, D. C., Simonen, J., Toppari, J. J.
Number of pages: 7
Pages: 317-323
Publication date: 9 Jul 2015
Peer-reviewed: Yes

Publication information

Journal: Organic Electronics
Volume: 25
ISSN (Print): 1566-1199
Ratings: 
  • Scopus rating (2015): CiteScore 3.6 SJR 1.135 SNIP 1.071
Original language: English
ASJC Scopus subject areas: Biomaterials, Electronic, Optical and Magnetic Materials, Materials Chemistry, Electrical and Electronic Engineering, Chemistry(all), Condensed Matter Physics
Keywords: PEDOT: PSS, Graphene, Anisotropy, Spectroscopy, Conducting polymer, CARBON-NANOTUBE, ELECTRONICS, OPTOELECTRONICS, CONDUCTIVITY, TRANSPARENT, PHOTONICS, GROWTH, CELLS

Bibliographical note

Versio ja lupa ok 13.1.2016 /KK
EXT="Simonen, Janne"

Source: Scopus
Source ID: 84936759109

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

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): 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

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

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

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

General information

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

Publication information

Journal: Physica C: Superconductivity and its Applications
Volume: 550
ISSN (Print): 0921-4534
Ratings: 
  • Scopus rating (2018): CiteScore 1.46 SJR 0.463 SNIP 0.922
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

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

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

General information

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

Publication information

Journal: Chemical Communications
Volume: 54
Issue number: 28
ISSN (Print): 1359-7345
Ratings: 
  • Scopus rating (2018): CiteScore 6.12 SJR 2.177 SNIP 1.145
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

Micro-Raman characterization of Germanium thin films evaporated on various substrates

We perform an extensive micro-Raman analysis of Germanium thin films physically evaporated on several substrates including silicon, silicon oxide and glass. We investigate the dependence of crystal quality on thin film deposition parameters such as substrate temperature and growth rate. We also study the continuous transitional change of the material structure from amorphous to crystalline phases. Ge films obtained by this simple and low cost technique are a viable solution towards the realization of virtual substrates and devices.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Frontier Photonics, University “Roma Tre”, Nonlinear Optics and OptoElectronics Lab, Universit Degli Studi dell'Aquila
Contributors: Sorianello, V., Colace, L., Assanto, G., Nardone, M.
Number of pages: 4
Pages: 492-495
Publication date: Apr 2011
Peer-reviewed: Yes

Publication information

Journal: Microelectronic Engineering
Volume: 88
Issue number: 4
ISSN (Print): 0167-9317
Ratings: 
  • Scopus rating (2011): CiteScore 1.8 SJR 0.813 SNIP 1.148
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials, Surfaces, Coatings and Films, Atomic and Molecular Physics, and Optics, Condensed Matter Physics
Keywords: Germanium, Raman characterization, Thin films
Source: Scopus
Source ID: 79751538206

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): 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

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

Multisoliton complexes in fiber lasers

The formation of stationary and non-stationary pulse groups is regularly observed in multiple pulse soliton fiber lasers. The environment developed in this study for the flexible investigation of this phenomenon is based on the cavity comprising a semiconductor saturable absorber mirror (SESAM) with complex dynamics of absorption recovery and all-fiber dispersion management. The detailed experimental and theoretical considerations show that multiple pulsing in fiber systems offers numerous embodiments ranging from stationary bound states to chaotic bunches. The pulse interaction through the dispersive waves was found to produce a principal impact on the bound state formation. The stability and transformation of stationary bound states and bunch propagation have been also addressed. (C) 2014 Elsevier Inc. All rights reserved.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Research group: Ultrafast and intense lasers, Optoelectronics Research Centre, Frontier Photonics, Ulyanovsk State Univ
Contributors: Korobko, D. A., Gumenyuk, R., Zolotovskii, I. O., Okhotnikov, O. G.
Number of pages: 17
Pages: 593-609
Publication date: Dec 2014
Peer-reviewed: Yes

Publication information

Journal: Optical Fiber Technology
Volume: 20
Issue number: 6
ISSN (Print): 1068-5200
Ratings: 
  • Scopus rating (2014): CiteScore 1.88 SJR 0.776 SNIP 1.317
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering
Keywords: Mode-locked fiber laser, Temporal solitons, Soliton dynamics, Nonlinear optics, Bound soliton pair, MODE-LOCKED LASERS, SATURABLE ABSORBER MIRRORS, BOUND SOLITONS, DISSIPATIVE SOLITONS, CAVITY DISPERSION, PULSE GENERATION, STATES, RAINS, PERTURBATIONS, PROPAGATION

Bibliographical note

Invited Paper<br/>Contribution: organisation=orc,FACT1=1<br/>Portfolio EDEND: 2014-11-11<br/>Publisher name: Academic Press

Source: researchoutputwizard
Source ID: 759

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

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

Near-infrared photodetectors in evaporated ge: Characterization and TCAD simulations

Thermal evaporation of germanium (Ge) on silicon (Si) has proved to be a suitable technique for the fabrication of high responsivity, low-cost, near-infrared pn detectors. Such results rely on low-temperature diffusion of n-type dopants. The corresponding transport phenomena are quite involved and cannot be described by standard models for pn junctions because of rather large defect concentration density in the Ge layer. In this paper, we report on fabrication, characterization, and simulation of defected Ge on Si photodiodes. For the simulations, we developed a technology computer aided design model and hereby demonstrate its ability to reproduce the measured optoelectronic characteristics of the devices.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Frontier Photonics, University “Roma Tre”, Univ Roma Tre, Roma Tre University, Dept Elect Engn, NooEL
Contributors: Sorianello, V., De Iacovo, A., Colace, L., Assanto, G.
Number of pages: 6
Pages: 1995-2000
Publication date: 2013
Peer-reviewed: Yes

Publication information

Journal: IEEE Transactions on Electron Devices
Volume: 60
Issue number: 6
Article number: 6515586
ISSN (Print): 0018-9383
Ratings: 
  • Scopus rating (2013): CiteScore 2.84 SJR 1.393 SNIP 1.744
Original language: English
ASJC Scopus subject areas: Electrical and Electronic Engineering, Electronic, Optical and Magnetic Materials
Keywords: Doping, near-infrared photodetectors, silicon germanium, technology computer aided design (TCAD), thermal evaporation
Source: Scopus
Source ID: 84878127050

Research output: Contribution to journalArticleScientificpeer-review

Near-surface defect profiling with slow positrons: Argon-sputtered Al(110)

We report on slow-positron measurements of atomic defect distribution near a solid surface. Defects are produced by argon-ion bombardment of an Al(110) surface in ultrahigh vacuum. Defect profiles have a typical width of 1525 A and contain a broader tail extending to 50100 A. The defect density at the outermost atomic layers saturates at high argon fluences to a few atomic percent, depending on sputtering conditions. Defect production rate at >1 keV Ar+ energies is typically 15 vacancy-interstitial pairs per incident ion. Molecular-dynamics simulations of the collision cascade predict similar defect distributions.

General information

Publication status: Published
MoE publication type: Not Eligible
Organisations: Laboratory of Physics, Jyväskylän yliopisto, Helsinki University of Technology, Aalto University
Contributors: Vehanen, A., Mäkinen, J., Hautojarvi, P., Huomo, H., Lahtinen, J., Nieminen, R. M., Valkealahti, S.
Number of pages: 3
Pages: 7561-7563
Publication date: 1 Jan 1985
Peer-reviewed: Yes

Publication information

Journal: Physical Review B
Volume: 32
Issue number: 11
ISSN (Print): 0163-1829
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Condensed Matter Physics
Source: Scopus
Source ID: 25044463128

Research output: Contribution to journalArticleScientificpeer-review

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

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

General information

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

Publication information

Journal: Semiconductor Science and Technology
Volume: 33
Issue number: 9
Article number: 094005
ISSN (Print): 0268-1242
Ratings: 
  • Scopus rating (2018): CiteScore 2.4 SJR 0.744 SNIP 1.014
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

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 5.67 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

Nonlinear optical activity effects in complex anisotropic three-dimensional media

We perform numerical modelling of nonlinear optical (NLO) microscopy of complex anisotropic three-dimensional (3D) media using the uncoupled dipole approximation. The modelling is applied to 3D biological microstructures resembling collagen fibers and multilamellar vesicles. The results elucidate how nonlinear optical activity effects, such as secondharmonic generation circular dichroism, can arise from 3D morphological chirality, in addition to molecular level chirality. We also show how thirdharmonic generation circular dichroism could act as a contrast mechanism for visualizing local structural ordering in 3D anisotropic materials.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Department of Physics, Tampere University of Technology, Research area: Optics, Research group: Nonlinear Optics, Frontier Photonics, Aalto University, National Taiwan University, Molecular Imaging Center, COMP Centre of Excellence, Department of Applied Physics, Aalto University
Contributors: Huttunen, M. J., Partanen, M., Bautista, G., Chu, S., Kauranen, M.
Number of pages: 11
Pages: 11-21
Publication date: 2015
Peer-reviewed: Yes

Publication information

Journal: Optical Materials Express
Volume: 5
Issue number: 1
ISSN (Print): 2159-3930
Ratings: 
  • Scopus rating (2015): CiteScore 3.07 SJR 1.34 SNIP 1.335
Original language: English
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials
Source: Scopus
Source ID: 84920996741

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

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, Physics, Tampere University, 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
Source: Scopus
Source ID: 85085038962

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 2.02 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

Observation of cavity structures in composite metamaterials

We investigated the cavity structure by the deformation of a unit cell of a Composite Metamaterial (CMM) structure. We considered different cavity structures with different resonance frequencies and Q-factors. We observed the Q-factor of the cavity resonance as 108 for a CMM based single cavity wherein the cavity structure is a closed ring structure. We investigated the reduced photon lifetime and observed that at the cavity resonance, the effective group velocity was reduced by a factor of 20 for a CMM based single cavity compared to the electromagnetic waves propagating in free space. Since the unit cells of metamaterials are much smaller than the operation wavelength, subwavelength localization is possible within these metamaterial cavity structures. We found that the electromagnetic field is localized into a region of/8, where is the cavity resonance wavelength. Subsequently, we brought two cavities together with an intercavity distance of two metamaterial unit cells and then investigated the transmission spectrum of CMM based interacting 2-cavity system. Finally, using the tight-binding picture we observed the normalized group velocity corresponding to the coupled cavity structure.

General information

Publication status: Published
MoE publication type: A1 Journal article-refereed
Organisations: Nanotechnology Research Center, Bilkent University
Contributors: Caglayan, H., Özbay, E.
Publication date: 2010
Peer-reviewed: Yes

Publication information

Journal: Journal of Nanophotonics
Volume: 4
Issue number: 1
Article number: 041790
Original language: English