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  • 1.
    Akansel, Serkan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Venugopal, Vijayaharan
    Kumar, Ankit
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gupta, Rahul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Brucas, Rimantas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    George, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Neagu, Alexandra
    Tai, Cheuk-Wai
    Gubbins, Mark
    Andersson, Gabriella
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Effect of seed layers on dynamic and static magnetic properties of Fe65Co35 thin films2018In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 30, article id 305001Article in journal (Refereed)
    Abstract [en]

    Fe65Co35 thin films have been deposited on SiO2 substrates using sputtering technique with different choices of seed layer; Ru, Ni82.5Fe17.5, Rh, Y and Zr. Best soft magnetic properties were observed with seed layers of Ru, Ni82.5Fe17.5 and Rh. Adding these seed layers, the coercivity of the Fe65Co35 films decreased to values of around 1.5 mT, which can be compared to the value of 12.5 mT obtained for films deposited without seed layer. Further investigations were performed on samples with these three seed layers in terms of dynamic magnetic properties, both on as prepared and annealed samples, using constant frequency cavity and broadband ferromagnetic resonance measurements. Damping parameters of around 8.0X10-3 and 4.5X10-3 were obtained from in-plane and out-of-plane measurements, respectively, for as prepared samples, values that were reduced to 6.5X10-3 and 4.0X10-3 for annealed samples.

  • 2.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A preliminary model to simulate negative leader dischargesIn: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463Article in journal (Refereed)
  • 3.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Preliminary study on the modelling of negative leader discharges2011In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 44, no 31, p. 315204-Article in journal (Refereed)
    Abstract [en]

    Nowadays, there is considerable interest in understanding the physics underlying positive and negative discharges because of the importance of improving lightning protection systems and of coordinating the insulation for high voltages. Numerical simulations of positive switching impulses made in long spark gaps in a laboratory are achievable because the physics of the process is reasonably well understood and because of the availability of powerful computational methods. However, the existing work on the simulation of negative switching discharges has been held up by a lack of experimental data and the absence of a full understanding of the physics involved. In the scientific community, it is well known that most of the lightning discharges that occur in nature are of negative polarity, and because of their complexity, the only way to understand them is to generate the discharges in laboratories under controlled conditions. The voltage impulse waveshape used in laboratories is a negative switching impulse. With the aim of applying the available information to a self-consistent physical method, an electrostatic approximation of the negative leader discharge process is presented here. The simulation procedure takes into consideration the physics of positive and negative discharges, considering that the negative leader propagates towards a grounded electrode and the positive leader towards a rod electrode. The simulation considers the leader channel to be thermodynamic, and assumes that the conditions required to generate a thermal channel are the same for positive and negative leaders. However, the magnitude of the electrical charge necessary to reproduce their propagation and thermalization is different, and both values are based on experimental data. The positive and negative streamer development is based on the constant electric field characteristics of these discharges, as found during experimental measurements made by different authors. As a computational tool, a finite element method based software is employed. The simulations are compared with experimental data available in the literature.

  • 4.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wu, Dong
    ABB Power Systems HVDC.
    A consistent approach to estimate the breakdown voltage of high voltage electrodes under positive switching impulses2013In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 114, no 8Article in journal (Refereed)
  • 5.
    Austgen, M
    et al.
    Institute of Physics (IA), RWTH Aachen University, Tyskland.
    Koehl, D
    Institute of Physics (IA), RWTH Aachen University, Tyskland.
    Zalden, P
    Institute of Physics (IA), RWTH Aachen University, Tyskland.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Nyberg, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Pflug, A
    Fraunhofer IST, Braunschweig, Tyskland.
    Siemers, M
    Fraunhofer IST, Braunschweig, Tyskland.
    Berg, Sören
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Wuttig, M
    Institute of Physics (IA), and, JARA-FIT, RWTH Aachen University, Tyskland.
    Sputter yield amplification by tungsten doping of Al(2)O(3) employing reactive serial co-sputtering: process characteristics and resulting film properties2011In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 44, no 34, p. 345501-Article in journal (Refereed)
    Abstract [en]

    The deposition rate of reactively sputtered Al(2)O(3) coatings is demonstrated to increase by 80% upon tungsten doping of the used aluminium target. This effect is based on the recoil of the sputtering species at implanted dopants below the target surface and is termed sputter yield amplification. For the investigation of this effect, a novel type of magnetron sputter deposition system is employed that facilitates serial co-sputtering. In this technique doping of the elementary target is enabled by a dynamic sputtering process from an auxiliary cathode. In our case, the rotating aluminium target is dynamically coated with tungsten from this auxiliary cathode. Since the primary target rotates, the auxiliary cathode is placed in series with the primary erosion zone. The deposition rate of Al(2)O(3) can be considerably increased in this process already for very low concentrations of approximately 1% of tungsten in the resulting film. A characterization of the dynamics of reactive sputtering as a function of target rotation speed is performed.

  • 6.
    Becerra, Marley
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    A self-consistent upward leader propagation model2006In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 39, no 16, p. 3708-3715Article in journal (Refereed)
    Abstract [en]

    The knowledge of the initiation and propagation of an upward moving connecting leader in the presence of a downward moving lightning stepped leader is a must in the determination of the lateral attraction distance of a lightning flash by any grounded structure. Even though different models that simulate this phenomenon are available in the literature, they do not take into account the latest developments in the physics of leader discharges. The leader model proposed here simulates the advancement of positive upward leaders by appealing to the presently understood physics of that process. The model properly simulates the upward continuous progression of the positive connecting leaders from its inception to the final connection with the downward stepped leader (final jump). Thus, the main physical properties of upward leaders, namely the charge per unit length, the injected current, the channel gradient and the leader velocity are self-consistently obtained. The obtained results are compared with an altitude triggered lightning experiment and there is good agreement between the model predictions and the measured leader current and the experimentally inferred spatial and temporal location of the final jump. It is also found that the usual assumption of constant charge per unit length, based on laboratory experiments, is not valid for lightning upward connecting leaders.

  • 7.
    Becerra, Marley
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Laboratory experiments cannot be utilized to justify the action of Early Streamer Emission terminals2008In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 41, no 8, p. 085204-Article in journal (Refereed)
    Abstract [en]

    The early emission of streamers in laboratory long air gaps under switching impulses has been observed to reduce the time of initiation of leader positive discharges. This fact has been arbitrarily extrapolated by the manufacturers of early streamer emission devices to the case of upward connecting leaders initiated under natural lightning conditions, in support of those non-conventional terminals that claim to perform better than Franklin lightning rods. In order to discuss the physical basis and validity of these claims, a self-consistent model based on the physics of leader discharges is used to simulate the performance of lightning rods in the laboratory and under natural lightning conditions. It is theoretically shown that the initiation of early streamers can indeed lead to the early initiation of self-propagating positive leaders in laboratory long air gaps under switching voltages. However, this is not the case for positive connecting leaders initiated from the same lightning rod under the influence of the electric field produced by a downward moving stepped leader. The time evolution of the development of positive leaders under natural conditions is different from the case in the laboratory, where the leader inception condition is closely dependent upon the initiation of the first streamer burst. Our study shows that the claimed similarity between the performance of lightning rods under switching electric fields applied in the laboratory and under the electric field produced by a descending stepped leader is not justified. Thus, the use of existing laboratory results to validate the performance of the early streamer lightning rods under natural conditions is not justified.

  • 8.
    Becerra, Marley
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Time dependent evaluation of the lightning upward connecting leader inception2006In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 39, no 21, p. 4695-4702Article in journal (Refereed)
    Abstract [en]

    The evaluation of the upward connecting leader inception from a grounded structure has generally been performed neglecting the effect of the propagation of the downward stepped leader. Nevertheless, field observations suggest that the space charge produced by streamer corona and aborted upward leaders during the approach of the downward lightning leader can influence significantly the initiation of stable upward positive leaders. Thus, a physical leader inception model is developed, which takes into account the electric field variations produced by the descending leader during the process of inception. Also, it accounts for the shielding effect produced by streamer corona and unstable leaders formed before the stable leader inception takes place. The model is validated by comparing its predictions with the results obtained in long gap experiments and in an altitude triggered lightning experiment. The model is then used to estimate the leader inception conditions for free standing rods as a function of tip radius and height. It is found that the rod radius slightly affects the height of the downward leader tip necessary to initiate upward leaders. Only an improvement of about 10% on the lightning attractiveness can be reached by using lightning rods with an optimum radius. Based on the obtained results, the field observations of competing lightning rods are explained. Furthermore, the influence of the average stepped leader velocity on the inception of positive upward leaders is evaluated. The results obtained show that the rate of change of the background electric field produced by a downward leader descent largely influences the conditions necessary for upward leader initiation. Estimations of the leader inception conditions for the upper and lower limit of the measured values of the average downward lightning leader velocity differ by more than 80%. In addition, the striking distances calculated taking into account the temporal change of the background field are significantly larger than the ones obtained assuming a static downward leader field. The estimations of the present model are also compared with the existing leader inception models and discussed.

  • 9.
    Benatto, L.
    et al.
    Univ Fed Parana, Dept Phys, CP 19044, BR-81531980 Curitiba, Parana, Brazil.
    Govatski, J. A.
    Univ Fed Parana, Dept Phys, CP 19044, BR-81531980 Curitiba, Parana, Brazil.
    de Moraes, C. A. M.
    Univ Fed Parana, Dept Phys, CP 19044, BR-81531980 Curitiba, Parana, Brazil.
    Gouvea, C. P.
    Pontifical Catholic Univ Rio de Janeiro, Dept Phys, BR-22453900 Rio De Janeiro, RJ, Brazil; Natl Inst Metrol Qual & Technol, Mat Metrol Div, BR-25250020 Duque De Caxias, RJ, Brazil.
    Avila, H. C.
    Pontifical Catholic Univ Rio de Janeiro, Dept Phys, BR-22453900 Rio De Janeiro, RJ, Brazil; Univ Atlantico, Programa Fis, Km 7 Via Puerto Colombia, Puerto Colombia 081001, Atlantico, Colombia.
    Marchiori, Cleber F. N.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Oliveira, C. K. B. Q. M.
    Univ Fed Parana, Dept Phys, CP 19044, BR-81531980 Curitiba, Parana, Brazil.
    Cremona, M.
    Pontifical Catholic Univ Rio de Janeiro, Dept Phys, BR-22453900 Rio De Janeiro, RJ, Brazil.
    Koehler, M.
    Univ Fed Parana, Dept Phys, CP 19044, BR-81531980 Curitiba, Parana, Brazil.
    Roman, L. S.
    Univ Fed Parana, Dept Phys, CP 19044, BR-81531980 Curitiba, Parana, Brazil.
    Understanding the effect of solvent additive in polymeric thin film: turning a bilayer into a bulk heterojunction-like photovoltaic device2020In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 53, no 36, article id 365101Article in journal (Refereed)
    Abstract [en]

    Here we report the effect of an additive solvent, 1,8-diiodooctane (DIO), on the performance of a bilayer organic photovoltaic device in which the active layer comprises poly[2,7-(9,9-bis(2 ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PSiF-DBT) as the electron donor material and C60 as the electron acceptor material. We observed that when the donor layer was treated with 1% of DIO the power conversion efficiency (PCE) of the device increased by 138.4% in relation to the device with an untreated donor layer, and 21.3% in relation to the device containing a donor layer submitted to thermal annealing. The main effects that lead to this increase in PCE are the large interfacial area between donor and acceptor materials and the improved conductivity at low voltages. The increase in polymer surface roughness leads to a more effective PSiF-DBT/C60 interface for exciton dissociation. This effect, as well as the increase in the conductivity, raised the short circuit current density (JSC) to 13.89 mA cm−2 and the PCE to 4.84%. Our conclusions are supported by morphological analysis, chemical cross-sectional evaluations with advanced microscopy techniques, charge mobility measurements, as well as by theoretical simulations of the devices in which the changes on the donor/acceptor interfacial area were considered. The outcomes suggest that solvent additives could be an alternative treatment to replace the thermal annealing, which imposes further difficulties in performing lab-to-manufacturing upscaling.

  • 10.
    Chen, Si
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Niemi, Antti J
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics. Univ Tours, Lab Math & Phys Theor, Federat Denis Poisson, CNRS UMR 6083, Parc Grandmont, F-37200 Tours, France.;Beijing Inst Technol, Dept Phys, Beijing 100081, Peoples R China..
    On Ramachandran angles, closed strings and knots in protein structure2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 31, article id 315401Article in journal (Refereed)
    Abstract [en]

    The Ramachandran angles (phi, psi) of a protein backbone form the vertices of a piecewise geodesic curve on the surface of a torus. When the ends of the curve are connected to each other similarly, by a geodesic, the result is a closed string that in general wraps around the torus a number of times both in the meridional and the longitudinal directions. The two wrapping numbers are global characteristics of the protein structure. A statistical analysis of the wrapping numbers in terms of crystallographic x-ray structures in the protein data bank (PDB) reveals that proteins have no net chirality in the phi direction but in the psi direction, proteins prefer to display chirality. A comparison between the wrapping numbers and the concept of folding index discloses a non-linearity in their relationship. Thus these three integer valued invariants can be used in tandem, to scrutinize and classify the global loop structure of individual PDB proteins, in terms of the overall fold topology.

  • 11. Coleman, V. A.
    et al.
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Grennberg, H.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Jansson, U.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Quinlan, R.
    Holloway, B. C.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Defect Formation In Graphene Nanosheets By Acid Treatment: An X-Ray Absorption Spectroscopy And Density Functional Theory Study2008In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 41, no 6, p. 062001-4Article in journal (Refereed)
    Abstract [en]

    In-plane defects have been introduced into graphene nanosheets by treatment with hydrochloric acid. Acid treatment induces bond cleavage in the C–C network via electrophilic attack. These resultant vacancy sites will then undergo further reactions with the surrounding ambient to produce C–O and C–H bonds. A σ* resonance at 287 eV in the carbon K-edge x-ray absorption spectra is observed with acid treatment and is assigned to C–O states. Theoretical modelling of a di-vacancy in a graphene bilayer reproduces all essential features of this resonance and in addition predicts a metallic conductivity of states around this vacancy. The possibility of engineering the properties of graphene via the routes explored here is an important step towards establishing strategies for building devices based on this material.

  • 12.
    Cramer, Joel
    et al.
    Johannes Gutenberg Univ Mainz, Inst Phys, D-55099 Mainz, Germany.;Grad Sch Excellence Mat Sci Mainz MAINZ, D-55128 Mainz, Germany..
    Ritzmann, Ulrike
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Konstanz, Dept Phys, D-78457 Constance, Germany..
    Dong, Bo-Wen
    Johannes Gutenberg Univ Mainz, Inst Phys, D-55099 Mainz, Germany.;Grad Sch Excellence Mat Sci Mainz MAINZ, D-55128 Mainz, Germany.;Univ Sci & Technol Beijing, Sch Mat Sci & Engn, Beijing 100083, Peoples R China..
    Jaiswal, Samridh
    Johannes Gutenberg Univ Mainz, Inst Phys, D-55099 Mainz, Germany.;Singulus Technol AG, D-63796 Kahl, Germany..
    Qiu, Zhiyong
    Dalian Univ Technol, Sch Mat Sci & Engn, Dalian 116024, Peoples R China..
    Saitoh, Eiji
    Tohoku Univ, Adv Inst Mat Res, Sendai, Miyagi 9808577, Japan.;Tohoku Univ, Inst Mat Res, Sendai, Miyagi 9808577, Japan.;Tohoku Univ, Ctr Spintron Res Network, Sendai, Miyagi 9808577, Japan.;Japan Atom Energy Agcy, Adv Sci Res Ctr, Tokai, Ibaraki 3191195, Japan..
    Nowak, Ulrich
    Univ Konstanz, Dept Phys, D-78457 Constance, Germany..
    Klaeui, Mathias
    Johannes Gutenberg Univ Mainz, Inst Phys, D-55099 Mainz, Germany.;Grad Sch Excellence Mat Sci Mainz MAINZ, D-55128 Mainz, Germany..
    Spin transport across antiferromagnets induced by the spin Seebeck effect2018In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 14, article id 144004Article in journal (Refereed)
    Abstract [en]

    For prospective spintronics devices based on the propagation of pure spin currents, antiferromagnets are an interesting class of materials that potentially entail a number of advantages as compared to ferromagnets. Here, we present a detailed theoretical study of magnonic spin current transport in ferromagnetic-antiferromagnetic multilayers by using atomistic spin dynamics simulations. The relevant length scales of magnonic spin transport in antiferromagnets are determined. We demonstrate the transfer of angular momentum from a ferromagnet into an antiferromagnet due to the excitation of only one magnon branch in the antiferromagnet. As an experimental system, we ascertain the transport across an antiferromagnet in Y3Fe5O12 vertical bar Ir20Mn80 vertical bar Pt heterostructures. We determine the spin transport signals for spin currents generated in the Y3Fe5O12 by the spin Seebeck effect and compare to measurements of the spin Hall magnetoresistance in the heterostructure stack. By means of temperature-dependent and thickness-dependent measurements, we deduce conclusions on the spin transport mechanism across Ir20Mn80 and furthermore correlate it to its paramagnetic-antiferromagnetic phase transition.

  • 13. Darbandi, Masih
    et al.
    Stromberg, Frank
    Landers, Joachim
    Reckers, Nathalie
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Keune, Werner
    Wende, Heiko
    Nanoscale size effect on surface spin canting in iron oxide nanoparticles synthesized by the microemulsion method2012In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, no 19, p. 195001-Article in journal (Refereed)
    Abstract [en]

    Uniformly sized and crystalline iron oxide nanoparticles (IONPs) with spinel structure and mean diameters of about 3, 6 and 9 nm were synthesized in high yield using the microemulsion route at room temperature. The nanoparticles (NPs) were stabilized in situ by organic surfactant molecules which acted both as a stabilizer of the microemulsion system and as a capping layer of the NP surface. NP size control was attained by careful adjustment of the preparation conditions. The structure, morphology and NP size distribution were investigated by x-ray diffraction, transmission electron microscopy and scanning electron microscopy. A particular effort was devoted in this work to study the effect of size and capping of these NPs on their magnetic structure by in-field Mossbauer spectroscopy at 4.2 K. The mean canting angle (relative to the applied field direction) of the Fe spins was observed to increase with decreasing NP size due to the enhanced surface-to-volume ratio. Comparing bare and capped NPs of the same diameter, we verified that the spin canting was not affected by the organic capping. This implied almost identical magnetic orientations of bare and capped NPs. Simultaneously, the capping material was capable of preventing agglomeration effects which can occur in case of direct particle contact. Using a core/shell model, we showed that spin canting originated from the surface shell of the NPs. Furthermore, the Mossbauer spectral parameters provided evidence for the existence of a high fraction of Fe3O4 (magnetite) in the IONP.

  • 14.
    Dastanpour, Esmat
    et al.
    KTH Royal Inst Technol, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden..
    Huang, Shuo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. China Univ Geosci, Fac Mat Sci & Chem, Wuhan 430074, Peoples R China.
    Schönecker, Stephan
    KTH Royal Inst Technol, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden..
    Mao, Huahai
    KTH Royal Inst Technol, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden.;Thermocalc Software AB, Rasundavagen 18, SE-16967 Solna, Sweden..
    Ström, Valter
    KTH Royal Inst Technol, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden..
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Örebro Univ, Sch Sci & Technol, SE-70182 Örebro, Sweden.
    Varga, Lajos Károly
    Wigner Res Ctr Phys, Inst Solid State Phys & Opt, H-1525 Budapest, Hungary..
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat Sci & Engn, SE-10044 Stockholm, Sweden; Wigner Res Ctr Phys, Inst Solid State Phys & Opt, H-1525 Budapest, Hungary.
    On the structural and magnetic properties of Al-rich high entropy alloys: a joint experimental-theoretical study2023In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 56, no 1, article id 015003Article in journal (Refereed)
    Abstract [en]

    The present work investigates how the vanadium (V) content in a series of Al50Vx(Cr0.33Mn0.33Co0.33)(50−x) (x = 12.5, 6.5, 3.5, and 0.5 at.%) high-entropy alloys affects the local magnetic moment and magnetic transition temperature as a step towards developing high-entropy functional materials for magnetic refrigeration. This has been achieved by carrying out experimental investigations on induction melted alloys and comparison to ab initio and thermodynamic calculations. Structural characterization by x-ray diffraction and scanning electron microscopy indicates a dual-phase microstructure containing a disordered body-centered cubic (BCC) phase and a B2 phase with long-range order, which significantly differ in the Co and V contents. Ab initio calculations demonstrate a weaker magnetization and lower magnetic transition temperature (TC) of the BCC phase in comparison with the B2 phase. We find that lower V content increases the B2 phase fraction, the saturation magnetization, and the Curie point, in line with the calculations. This trend is primarily connected with the preferential partition of V in the BCC phase, which however hinders the theoretically predicted antiferromagnetic B2 phase stabilizing effect of V. On the other hand, the chemistry-dependent properties of the ferromagnetic B2 phase suggest that a careful tuning of the composition and phase fractions can open the way towards promising high-entropy magnetic materials.

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  • 15. Ehiasarian, Arutiun P.
    et al.
    Andersson, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Anders, Andre
    Distance-dependent plasma composition and ion energy in high power impulse magnetron sputtering2010In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 43, no 27, p. 275204-Article in journal (Refereed)
    Abstract [en]

    The plasma composition of high power impulse magnetron sputtering (HIPIMS) has been studied for titanium and chromium targets using a combined energy analyser and quadrupole mass spectrometer. Measurements were done at distances from 50 to 300 mm from the sputtering target. Ti and Cr are similar in atomic mass but have significantly different sputter yields, which gives interesting clues on the effect of the target on plasma generation and transport of atoms. The Ti and Cr HIPIMS plasmas operated at a peak target current density of similar to 0.5 A cm(-2). The measurements of the argon and metal ion content as well as the ion energy distribution functions showed that (1) singly and doubly charged ions were found for argon as well as for the target metal, (2) the majority of ions were singly charged argon for both metals at all distances investigated, (3) the Cr ion density was maintained to distances further from the target than Ti. Gas rarefaction was identified as a main factor promoting transport of metal ions, with the stronger effect observed for Cr, the material with higher sputter yield. Cr ions were found to displace a significant portion of the gas ions, whereas this was less evident in the Ti case. The observations indicate that the presence of metal vapour promotes charge exchange and reduces the electron temperature and thereby practically prevents the production of Ar2+ ions near the target. The content of higher charge states of metal ions depends on the probability of charge exchange with argon.

  • 16.
    Eriksson, Sandra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Eklund, P.
    Halmstad Univ, Rydberg Lab Appl Sci, POB 823, SE-30118 Halmstad, Sweden..
    Effect of magnetic properties on performance of electrical machines with ferrite magnets2021In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 54, no 5, article id 054001Article in journal (Refereed)
    Abstract [en]

    The increased focus on ferrite magnets makes it interesting to investigate their suitability in electrical machines such as generators for wind power and motors for electric cars. Efforts are currently being made to improve the magnetic properties of ferrites. A simulation method is used to investigate how different magnetic properties such as remanence, coercivity and intrinsic coercivity affect the performance of electrical machines, here quantified as output torque. It is also ensured that the magnet is not partly demagnetized during a short-circuit event. Simulations are performed through a two-dimensional finite-element-based simulation method. Not all combinations of magnetic properties will render a usable design and it is therefore investigated how high the required values are for different magnetic properties as well as how high an output torque can be achieved. It is concluded that increasing the remanence or the coercivity can be quantified as an improved energy product, whereas improvement of the intrinsic coercivity enables the magnet to have a more optimal shape and thereby have a working point where the energy product is maximized. In addition it is found that for a fixed available magnetic energy, the performance does not change significantly with increasing remanence.

  • 17.
    Evertz, S.
    et al.
    Max Planck Inst Eisenforsch GmbH, Max Planck Str 1, D-40237 Dusseldorf, Germany..
    Nicolin, N.
    Max Planck Inst Eisenforsch GmbH, Max Planck Str 1, D-40237 Dusseldorf, Germany..
    Cheng, N.
    Max Planck Inst Eisenforsch GmbH, Max Planck Str 1, D-40237 Dusseldorf, Germany..
    Primetzhofer, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Best, J. P.
    Max Planck Inst Eisenforsch GmbH, Max Planck Str 1, D-40237 Dusseldorf, Germany..
    Dehm, G.
    Max Planck Inst Eisenforsch GmbH, Max Planck Str 1, D-40237 Dusseldorf, Germany..
    Phase formation and electrical properties of reactively sputtered Fe1-x O thin films2024In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 57, no 6, article id 065302Article in journal (Refereed)
    Abstract [en]

    Wustite, Fe1-x O, is a crucial phase for the transition to CO2-free steel manufacturing as well as promising for electrochemical applications such as water splitting and ammonia synthesis. To study the effect of interfaces in these applications, thin-film model systems with defined interfaces are ideal. Previous studies lack a description of the growth mechanism to obtain Fe1-x O thin films. Here, we investigate the phase formation of metastable Fe1-x O during reactive magnetron sputtering while systematically varying the O-2/Ar flow ratio from 1.8% to 7.2% and the pressure-distance product between 3.5 and 7.2 Pa cm. If bulk diffusion is minimized, thin films containing 96 vol.% wustite and 4 vol.% Fe as impurity phase were achieved. Therefore, the wustite phase formation appears to be surface diffusion dominated. To reveal the influence of impurity phases in wustite on the electrical resistivity, systematic electrical resistivity measurements while cooling in situ were performed for the first time. The electrical resistivity was lower than that of single crystals of the respective iron oxides. This is attributed to the formation of Fe-rich layers at the substrate-film interface, which serve as additional conduction paths.

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  • 18.
    Fallberg, Anna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Ottosson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Endrino, Jose Luis
    Instituto de Ciencia de Materiales de Madrid.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Andersson, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
    Carlsson, Jan-Otto
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
     A NEXAFS and XPS study of oxygen doped Cu3NIn: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463Article in journal (Refereed)
    Abstract [en]

    Thin films of pure and oxygen doped Cu3N, deposited by Chemical Vapour Deposition, have been studied with the NEXAFS technique both in the FLY and TEY mode and compared with XPS results.  Cu, CuO and Cu2O have been used as reference samples in the investigation for detection of surface oxidation and contaminants. The aim has been to investigate how and if the chemical environment changes around Cu, N and O upon incorporation of oxygen in the Cu3N lattice. The recorded NEXAFS spectra are discussed in terms of valence electrons, crystal structure and local bonding environment. It was found that basically two oxygen absorption sites are possible in the crystal structure, (½, ½, 0) and (¼, ¼, ¼), and that the oxygen distribution between the two sites is probably given by the oxygen concentration.

  • 19.
    Fornell, Anna
    et al.
    Uppsala University, Science for Life Laboratory, SciLifeLab. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology. Lund Univ, MAX Lab 4, S-22484 Lund, Sweden.
    Baasch, Thierry
    Lund Univ, Dept Biomed Engn, S-22100 Lund, Sweden.
    Johannesson, Carl
    Lund Univ, Dept Biomed Engn, S-22100 Lund, Sweden.
    Nilsson, Johan
    Lund Univ, Dept Biomed Engn, S-22100 Lund, Sweden.
    Tenje, Maria
    Uppsala University, Science for Life Laboratory, SciLifeLab. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology.
    Binary acoustic trapping in a glass capillary2021In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 54, no 35, article id 355401Article in journal (Refereed)
    Abstract [en]

    Acoustic trapping is a useful method for handling biological samples in microfluidic systems. The aim of this work is twofold: first to investigate the physics behind acoustic trapping in a glass capillary and secondly to perform binary acoustic trapping. The latter is achieved by increasing the density of the fluid in the trapping channel. The trapping device consisted of a glass capillary with a rectangular inner cross-section (height 200 µm × width 2000 µm) equipped with a small piezoelectric transducer. The piezoelectric transducer was actuated at 4 MHz to generate a localised half-wavelength acoustic standing-wave-field in the capillary, comprising of a pressure field and a velocity field. Under acoustic actuation, only particles with higher density than the fluid, i.e. having a positive dipole scattering coefficient, were trapped in the flow direction. The numerical and analytical modelling of the system show that the trapping force which retains the particles against the flow depends only on the dipole scattering coefficient in the pressure nodal plane of the acoustic field. The analytical model also reveals that the retention force is proportional to the dipole scattering coefficient, which agrees with our experimental findings. Next, we showed that in a mixture of melamine particles and polystyrene particles in a high-density fluid it is possible to selectively trap melamine particles, since melamine particles have higher density than polystyrene particles.

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  • 20.
    Frisk, Andreas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Hase, Thomas P.A.
    Department of Physics, University of Warwick, Coventry, CV4 7AL, United Kingdom.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Johansson, Erik
    ABB AB, Power Devices, Corporate Research, SE-721 78 Västerås, Sweden.
    Andersson, Gabriella
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Strain Engineering for Controlled Growth of Thin-Film FeNi L102017In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 50, no 8, article id 085009Article in journal (Refereed)
    Abstract [en]

    FeNi thin films in the L1(0) phase were successfully grown by magnetron sputtering on HF-etched Si(001) substrates on Cu/Cu100-xNix buffers. The strain of the FeNi layer, (c/a)(FeNi), was varied in a controlled manner by changing the Ni content of the Cu100-xNix buffer layer from x = 0 at.% to x = 90 at.%, which influenced the common in- plane lattice parameter of the CuNi and FeNi layers. The presence of the L1(0) phase was confirmed by resonant x-ray diffraction measurements at various positions in reciprocal space. The uniaxial magnetocrystalline anisotropy energy K-U is observed to be smaller (around 0.35 MJ m(-3)) than predicted for a perfect FeNi L1(0) sample, but it is larger than for previously studied films. No notable variation in K-U with strain state (c/a)(FeNi) is observed in the range achieved (0.99 less than or similar to (c/a)(FeNi) less than or similar to 1.02), which is in agreement with theoretical predictions.

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    [Frisk et al](2017)Proof_10.1088_1361-6463_aa5629
  • 21.
    Frisk, Andreas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Magnus, Fridrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    George, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Arnalds, Unnar B
    Andersson, Gabriella
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Tailoring anisotropy and domain structure in amorphous TbCo thin films through combinatorial methods2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 3, article id 035005Article in journal (Refereed)
    Abstract [en]

    We apply an in-plane external magnetic field during growth of amorphous TbCo thin films and examine the effects on the magnetic anisotropy and domain structure. A combinatorial approach is employed throughout the deposition and analysis to study a continuous range of compositions between 7–95 at.% Tb. Magnetometry measurements show that all samples have a strong out-of-plane anisotropy, much larger than any in-plane components, regardless of the presence of a growth field. However, magnetic force microscopy demonstrates that the growth field does indeed have a large effect on the magnetic domain structure, resulting in elongated domains aligned along the imprinting field direction. The results show that the anisotropy can be tuned in intricate ways in amorphous TbCo films giving rise to unusual domain structures. Furthermore the results reveal that a combinatorial approach is highly effective for mapping out these material properties.

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  • 22.
    Frisk, Christopher
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Olsson, Jörgen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Szaniawski, Piotr
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Wätjen, Timo
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Fjällström, Viktor
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Salome, P.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Optimizing Ga-profiles for highly efficient Cu(In,Ga)Se2 thin film solar cells in simple and complex defect models2014In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 47, no 48, p. 485104-Article in journal (Refereed)
    Abstract [en]

    Highly efficient Cu(In,Ga)(S,Se)2 photovoltaic thin film solar cells often have a compositional variation of Ga to In in the absorber layer, here described as a Ga-profile. In this work we have studied the role of Ga-profiles in four different models, based on input data from electrical and optical characterizations of an in-house state-of-the-art Cu(In,Ga)Se2 (CIGS) solar cell with power conversion efficiency above 19 %. A simple defect model with mid-gap defects in the absorber layer was compared with models with Ga-dependent defect concentrations and amphoteric defects. In these models optimized single-graded Ga-profiles have been compared with optimized double-graded Ga-profiles. It was found that the defect concentration for effective Shockley-Read-Hall recombination is low for high efficiency CIGS devices and that the doping concentration of the absorber layer, chosen according to the defect model, is paramount when optimizing Ga-profiles. For optimized single-graded Ga-profiles the simulated power conversion efficiency, depending on the model, is 20.5-20.8 %, and the equivalent double-graded Ga-profiles yield 20.6-21.4 %, indicating that the bandgap engineering of the CIGS device structure can lead to improvements in efficiency. Apart from the effects of increased doping in the complex defect models, the results are similar when comparing the complex defect models to the simple defect models. 

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    Optimizing_Ga-profiles_2014
  • 23.
    Gruenebohm, A.
    et al.
    Univ Duisburg Essen, Fac Phys, D-47048 Duisburg, Germany.;Univ Duisburg Essen, CENIDE, D-47048 Duisburg, Germany..
    Herper, Heike C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Entel, P.
    Univ Duisburg Essen, Fac Phys, D-47048 Duisburg, Germany.;Univ Duisburg Essen, CENIDE, D-47048 Duisburg, Germany..
    On the rich magnetic phase diagram of (Ni, Co)-Mn-Sn Heusler alloys2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 39, article id 395001Article in journal (Refereed)
    Abstract [en]

    We put a spotlight on the exceptional magnetic properties of the metamagnetic Heusler alloy (Ni, Co)-Mn-Sn by means of first principles simulations. In the energy landscape we find a multitude of local minima, which belong to different ferrimagnetic states and are close in total magnetization and energy. All these magnetic states correspond to the local high spin state of the Mn atoms with different spin alignments and are related to the magnetic properties of Mn. Compared to pure Mn, the magneto-volume coupling is reduced by Ni, Co and Sn atoms in the lattice and no local low-spin Mn states appear. For the cubic phase we find a ferromagnetic ground state whereas the global energy minimum is a tetragonal state with a complicated spin structure and vanishing magnetization which so far has been overlooked in simulations.

  • 24. Horwat, David
    et al.
    Jullien, Maud
    Capon, Fabien
    Pierson, Jean-Francois
    Andersson, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Luis Endrino, Jose
    On the deactivation of the dopant and electronic structure in reactively sputtered transparent Al-doped ZnO thin films2010In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 43, no 13, p. 132003-Article in journal (Refereed)
    Abstract [en]

    We report on the possible origin of electrical heterogeneities in 4 at% Al-doped ZnO (AZO) reactively sputtered films. It is found through the Zn L-3 and Al K edge x-ray absorption near-edge structure that a fraction of the Al dopant is deactivated by its positioning in octahedral conformation with oxygen. This fraction as well as the conductivity, optical bandgap and c-axis parameter of ZnO wurtzite are all found to depend on the sample position during deposition. The present results suggest the formation of a metastable Al2O3 (ZnO) m homologous phase that degrades the electrical conductivity.

  • 25.
    Huang, Shuo
    et al.
    China Univ Geosci, Fac Mat Sci & Chem, Wuhan 430074, Peoples R China..
    Cheng, Jie
    China Univ Min & Technol Beijing, Sch Mech Elect & Informat Engn, Beijing 100083, Peoples R China..
    Liu, Lei
    China Acad Engn Phys, Inst Fluid Phys, Lab Shock Wave & Detonat Phys, Mianyang 621900, Sichuan, Peoples R China..
    Li, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jin, Hongyun
    China Univ Geosci, Fac Mat Sci & Chem, Wuhan 430074, Peoples R China..
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.;Wigner Res Ctr Phys, Inst Solid State Phys & Opt, H-1525 Budapest, Hungary..
    Thermo-elastic behavior of hexagonal Sc-Ti-Zr-Hf high-entropy alloys2022In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 55, no 23, article id 235302Article in journal (Refereed)
    Abstract [en]

    Recent advances in tuning the long-standing strength-ductility tradeoff have drawn attention to high-entropy alloys (HEAs), and the appearance of hexagonal close-packed (hcp) structures has been emphasized. However, few studies have explored the elastic moduli of hcp HEAs, which is of prime importance for improved understanding of the outstanding mechanical properties. In this work, we focus on a set of equiatomic rare-earth-free HEAs with hcp structures, i.e. ScTiZr, ScTiHf, ScZrHf, TiZrHf, and ScTiZrHf, and their thermo-elastic properties are studied using quantum mechanical first-principles methods. It is found that, for all considered HEAs, the hexagonal axial ratio shows a weak dependence on the temperature effect, and the thermal expansion coefficient remains almost unchanged above room temperature. From the calculated temperature-dependent single-crystal elastic constants, we analyzed the mechanical stability, elastic anisotropy, and derived polycrystalline moduli. Results indicate that the present HEAs exhibit rather high elastic isotropy and large elastic softening resistance. The ab initio predicted Young's modulus, shear modulus, and specific modulus do not obey the rule of mixture, which indicates that there exists a strong intrinsic hardening effect in all of the considered HEAs. The calculated results are in good agreement with the available experimental measurements.

  • 26.
    Ivanov, Sergey A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Karpov Inst Phys Chem, Ctr Mat Sci, Moscow 105064, Russia..
    Ritter, C.
    Inst Laue Langevin, BP 156, F-38042 Grenoble, France..
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Tellgren, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Weil, M.
    Vienna Univ Technol, Inst Chem Technol & Analyt, A-1060 Vienna, Austria..
    Carolus, V.
    Univ Bonn, HISKP, Nussallee 14-16, D-53115 Bonn, Germany..
    Lottermoser, Th
    ETH, Dept Mat, Vladimir Prelog Weg 4, CH-8093 Zurich, Switzerland..
    Fiebig, M.
    ETH, Dept Mat, Vladimir Prelog Weg 4, CH-8093 Zurich, Switzerland..
    Mathieu, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    New insights into the multiferroic properties of Mn3TeO62017In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 50, no 8, article id 085001Article in journal (Refereed)
    Abstract [en]

    Mn3TeO6 has a trigonal corundum related structure (space group R (3) over bar), and orders in an incommensurate antiferromagnetic (AFM) structure at T-N approximate to 24 K. A weak ferroelectric order below T* similar to 21 K has recently been reported. In order to investigate possible structural changes below T-N leading to the observed dipole order, we have performed a detailed study of the crystal and magnetic structures of Mn3TeO6 using neutron powder diffraction (NPD) in the temperature range of 5-40 K. Complementary low-temperature second harmonic generation (SHG) measurements were performed in order to confirm the reported dipole order at T*. No change in the rhombohedral symmetry associated with a possible displacive phase transition at T* was observed in the long-range structural correlations, and it appears that Mn3TeO6 keeps the same incommensurately modulated magnetic spin structure with the propagation vector k = (0; 0; 0.43) in the whole temperature range from 5 to 24 K.

  • 27.
    Jablonka, Lukas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Moskovkin, Pavel
    Laboratoire d'Analyse par Réactions Nucléaires (LARN), Namur Institute of Structured Matter (NISM), University of Namur (UNamur), Namur, Belgium.
    Zhang, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zhang, Shi-Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Lucas, Stéphane
    Laboratoire d'Analyse par Réactions Nucléaires (LARN), Namur Institute of Structured Matter (NISM), University of Namur (UNamur), Namur, Belgium.
    Kubart, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Metal Filling by High Power Impulse Magnetron Sputtering2019In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 52, no 36, article id 365202Article in journal (Refereed)
    Abstract [en]

    High power impulse magnetron sputtering (HiPIMS) is an emerging thin film deposition technology that provides a highly ionized flux of sputtered species. This makes HiPIMS attractive for metal filling of nanosized holes for highly scaled semiconductor devices. In this work, HiPIMS filling with Cu and Co is investigated. We show that the quality of the hole filling is determined mainly by the fraction of ions in the deposited flux and their energy. The discharge waveforms alone are insufficient to determine the ionization of the metal flux. The experimental results are in a good agreement with Monte-Carlo simulations using the measured flux characteristics. Based on the simulations, strategies to improve the filling are discussed.

  • 28.
    Jafri, Syed Hassan Mujtaba
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Carva, Karel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Widenkvist, Erika
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Blom, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Jansson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Grennberg, Helena
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Quinlan, Ronald A
    College of William and Mary, Williamsburg VA, USA.
    Holloway, Brian C
    Luna Innovations, Danville, VA, USA.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Conductivity engineering of graphene by defect formation2010In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 43, no 4, p. 045404-Article in journal (Refereed)
    Abstract [en]

    Transport measurements have revealed several exotic electronic properties of graphene. The possibility to influence the electronic structure and hence control the conductivity by adsorption or doping with adatoms is crucial in view of electronics applications. Here, we show that in contrast to expectation, the conductivity of graphene increases with increasing concentration of vacancy defects, by more than one order of magnitude. We obtain a pronounced enhancement of the conductivity after insertion of defects by both quantum mechanical transport calculations as well as experimental studies of carbon nano-sheets. Our finding is attributed to the defect induced mid-gap states, which create a region exhibiting metallic behaviour around the vacancy defects. The modification of the conductivity of graphene by the implementation of stable defects is crucial for the creation of electronic junctions in graphene-based electronics devices.

  • 29.
    Keatley, Paul Steven
    et al.
    Univ Exeter, Dept Phys & Astron, Stocker Rd, Exeter EX4 4QL, Devon, England..
    Sani, Sohrab Redjai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. KTH Royal Inst Technol, Sch ICT, Mat & Nano Phys, Electrum 229, S-16460 Kista, Sweden.;NanOsc AB, Electrum 205, S-16440 Kista, Sweden..
    Hrkac, Gino
    Univ Exeter, Coll Engn Math & Phys Sci, Exeter EX4 4SB, Devon, England..
    Mohseni, Seyed Majid
    Shahid Beheshti Univ, GC Evin, Dept Phys, Tehran 19839, Iran..
    Durrenfeld, Philipp
    Univ Gothenburg, Dept Phys, Fys Grand 3, S-41296 Gothenburg, Sweden..
    Åkerman, Johan
    KTH Royal Inst Technol, Sch ICT, Mat & Nano Phys, Electrum 229, S-16460 Kista, Sweden.;NanOsc AB, Electrum 205, S-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, Fys Grand 3, S-41296 Gothenburg, Sweden..
    Hicken, Robert James
    Univ Exeter, Dept Phys & Astron, Stocker Rd, Exeter EX4 4QL, Devon, England..
    Imaging magnetisation dynamics in nano-contact spin-torque vortex oscillators exhibiting gyrotropic mode splitting2017In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 50, no 16, article id 164003Article in journal (Refereed)
    Abstract [en]

    Nano-contact spin-torque vortex oscillators (STVOs) are anticipated to find application as nanoscale sources of microwave emission in future technological applications. Presently the output power and phase stability of individual STVOs are not competitive with existing oscillator technologies. Synchronisation of multiple nano-contact STVOs via magnetisation dynamics has been proposed to enhance the microwave emission. The control of device-to-device variations, such as mode splitting of the microwave emission, is essential if multiple STVOs are to be successfully synchronised. In this work a combination of electrical measurements and time-resolved scanning Kerr microscopy (TRSKM) was used to demonstrate how mode splitting in the microwave emission of STVOs was related to the magnetisation dynamics that are generated. The free-running STVO response to a DC current only was used to identify devices and bias magnetic field configurations for which single and multiple modes of microwave emission were observed. Stroboscopic Kerr images were acquired by injecting a small amplitude RF current to phase lock the free-running STVO response. The images showed that the magnetisation dynamics of a multimode device with moderate splitting could be controlled by the injected RF current so that they exhibit similar spatial character to that of a single mode. Significant splitting was found to result from a complicated equilibrium magnetic state that was observed in Kerr images as irregular spatial characteristics of the magnetisation dynamics. Such dynamics were observed far from the nano-contact and so their presence cannot be detected in electrical measurements. This work demonstrates that TRSKM is a powerful tool for the direct observation of the magnetisation dynamics generated by STVOs that exhibit complicated microwave emission. Characterisation of such dynamics outside the nano-contact perimeter permits a deeper insight into the requirements for optimal phase-locking of multiple STVOs that share common magnetic layers.

  • 30.
    Kosyak, Volodymyr
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solar Cell Technology.
    Ross, N.
    Univ Oslo, N-0316 Oslo, Norway.
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solar Cell Technology.
    Current-voltage and capacitance study of light-induced metastabilities in CuZnSnSSe thin film solar cells2020In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 53, no 18, article id 185108Article in journal (Refereed)
    Abstract [en]

    White, red and blue light-induced metastabilities in Cu2ZnSnS(4)(Se-4) solar cells were investigated by temperature dependent current-voltage measurements, drive level capacitance profiling, impedance and thermal admittance spectroscopy. A set of devices were studied where white and blue light soaking at room temperature led to degradation of the device performance, while after red light soaking the solar cell efficiency did not change. We observed a significant effect of light soaking on capacitance data measured in both low and high-temperature ranges for these devices. In particular, the net doping concentration extracted from drive-level capacitance profiling substantially increased after light soaking treatments. Low and high-temperature capacitance steps observed in the reference capacitance-frequency spectra were assigned to Fermi level pinning and bulk defects, correspondingly. Light soaking with different-wavelength light led to a shift of both steps toward the high-frequency range, and hence a decrease in the thermal admittance activation energies. A low-frequency 'inductive' loop was detected in the impedance spectra after light soaking, regardless of wavelength. It was proposed that the appearance of the 'inductive' loop is due to the formation of a negative electric field at the highly defected CdS/Cu2ZnSnS(4)(Se-4) hetero-interface. This result also leads us to conclude that such electric field is responsible for the metastable behaviour of these devices at room temperature, while the low temperature metastable changes might have a different origin. We also discuss the methodology for electrical characterization of the metastable solar cells in detail.

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  • 31. Krysztopa, A
    et al.
    Igalson, M
    Larsen, Jes K
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Aida, Y
    Gütay, L
    Siebentritt, S
    Photoinduced current transient spectroscopy of defect levels in CuInSe2 and CuGaSe2 epitaxial and polycrystalline layers2012In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, no 33, p. 335101-Article in journal (Refereed)
  • 32.
    Kubart, Tomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Nyberg, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Berg, Sören
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Modelling of low energy ion sputtering from oxide surfaces2010In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 43, no 20, p. 205204-Article in journal (Refereed)
    Abstract [en]

    The main aim of this work is to present a way to estimate the values of surface binding energy for oxides. This is done by fitting results from the binary collisions approximation code Tridyn with data from the reactive sputtering processing curves, as well as the elemental composition obtained from x-ray photoelectron spectroscopy (XPS). Oxide targets of Al, Ti, V, Nb and Ta are studied. The obtained surface binding energies are then used to predict the partial sputtering yields. Anomalously high sputtering yield is observed for the TiO 2 target. This is attributed to the high sputtering yield of Ti lower oxides. Such an effect is not observed for the other studied metals. XPS measurement of the oxide targets confirms the formation of suboxides during ion bombardment as well as an oxygen deficient surface in the steady state. These effects are confirmed from the processing curves from the oxide targets showing an elevated sputtering rate in pure argon.

  • 33.
    Kumar, Ankit
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Behera, Nilamani
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Gupta, Rahul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Husain, Sajid
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Stopfel, Henry
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Kapaklis, Vassilios
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Brucas, Rimantas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Impact of the crystal orientation on spin-orbit torques in Fe/Pd bilayers2020In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 53, no 35, article id 355003Article in journal (Refereed)
    Abstract [en]

    Spin-orbit torques in ferromagnetic/non-magnetic heterostructures offer more energy-efficient means to realize spin-logic devices; however, their strengths are determined by the heterostructure interface. This work examines the impact of crystal orientation on the spin-orbit torque efficiency in different Fe/Pd bilayer systems. Results from spin torque ferromagnetic resonance measurements evidence that the damping-like torque efficiency is higher in epitaxial than in polycrystalline bilayer structures while the field-like torque is negligible in all bilayer structures. The strength of the damping-like torque decreases with deterioration of the bilayer epitaxial quality. The present finding provides fresh insight for the enhancement of spin-orbit torques in magnetic heterostructures.

  • 34.
    Liao, Xiaoqi
    et al.
    Shenzhen Univ, Coll Phys & Optoelect Engn, Shenzhen 518060, Peoples R China.;Hanshan Normal Univ, Sch Mat Sci & Engn, Chaozhou 521041, Peoples R China..
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Salazar-Alvarez, German
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Zeng, Yu-Jia
    Shenzhen Univ, Coll Phys & Optoelect Engn, Shenzhen 518060, Peoples R China..
    Huang, Rui
    Hanshan Normal Univ, Sch Mat Sci & Engn, Chaozhou 521041, Peoples R China..
    Yang, Sen
    Xi An Jiao Tong Univ, MOE Key Lab Nonequilibrium Synth & Modulat Conden, Xian 710049, Peoples R China.;Xi An Jiao Tong Univ, State Key Lab Mech Behav Mat, Xian 710049, Peoples R China..
    Wang, Yu
    Xi An Jiao Tong Univ, MOE Key Lab Nonequilibrium Synth & Modulat Conden, Xian 710049, Peoples R China.;Xi An Jiao Tong Univ, State Key Lab Mech Behav Mat, Xian 710049, Peoples R China..
    Giant exchange bias in micro-sized magnetic shape memory alloy particles2021In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 54, no 4, article id 045001Article in journal (Refereed)
    Abstract [en]

    We report the effects of the magnetic ground sate and microstructure on exchange bias (EB) in ball milled Ni44Co6Mn39.5Sn10.5 alloys. A giant bias field of 1.49 T has been obtained for the micron-sized particles after 15 h milling, which is considerably larger than that of 2 h milled platelets (0.35 T) and that of the bulk alloy (0.12 T). This giant bias field is attributed to the increased volume fraction of antiferromagnetic/ferromagnetic interface, the enhanced antiferromagnetic fraction and the formed agglomerates. Our results reveal the critical roles of the magnetic ground state and microstructure of milled alloys in determining EB.

  • 35.
    Lindström, A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Mirbt, Susanne
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Klintenberg, Mattias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    High resistivity in undoped CdTe: carrier compensation of Te antisites and Cd vacancies2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 3, article id 035101Article in journal (Refereed)
    Abstract [en]

    In this paper, we focus on the high resistivity of intentionally undoped CdTe, where the most prevalent defects are Cd vacancies and Te antisites. Our calculated formation energies lead to the conclusion that the Fermi energy of undoped CdTe is at midgap due to carrier compensation of Te antisites and Cd vacancies, which explains the experimentally observed high resistivity. We use density functional theory with the hybrid functional of Heyd, Scuseria and Ernzerhof (HSE06) and show that the proper description of the native defects in general fails using the local density approximation (LDA) instead of HSE06. We conclude that LDA is insufficient to understand the high resistivity of undoped CdTe. We calculate the neutral and double acceptor state of the Te antisite to be intrinsic DX-centers.

  • 36.
    Linnarsson, M. K.
    et al.
    KTH Royal Inst Technol, Mat Phys, Electrum 229, SE-16440 Kista, Sweden..
    Hallen, A.
    KTH Royal Inst Technol, Sch Informat & Commun Technol, Electrum 229, SE-16440 Kista, Sweden..
    Khartsev, S.
    KTH Royal Inst Technol, Sch Informat & Commun Technol, Electrum 229, SE-16440 Kista, Sweden..
    Suvanam, Sethu Saveda
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. KTH Royal Inst Technol, Sch Informat & Commun Technol, Electrum 229, SE-16440 Kista, Sweden.
    Usman, M.
    KTH Royal Inst Technol, Sch Informat & Commun Technol, Electrum 229, SE-16440 Kista, Sweden.;Quaid I Azam Univ, Natl Ctr Phys, Expt Phys Lab, Islamabad, Pakistan..
    Interface between Al2O3 and 4H-SiC investigated by time-of-flight medium energy ion scattering2017In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 50, no 49, article id 495111Article in journal (Refereed)
    Abstract [en]

    The formation of interfacial oxides during heat treatment of dielectric films on 4H-SiC has been studied. The 4H-SiC surface has been carefully prepared to create a clean and abrupt interface to Al2O3. An amorphous, 3 nm thick, Al2O3 film has been prepared on 4H-SiC by atomic layer deposition and rapid thermal annealing was then performed in N2O ambient at 700 degrees C and 1100 degrees C during 1 min. The samples were studied by time-of-flight medium energy ion scattering (ToF-MEIS), with sub-nanometer depth resolution and it is seen that, at both annealing temperatures, a thin SiOx (1 <= x <= 2) is formed at the interface. Our results further indicate that carbon remains in the silicon oxide in samples annealed at 700 degrees C. Additional electrical capacitance voltage measurements indicate that a large concentration of interface traps is formed at this temperature. After 1100 degrees C annealing, both MEIS and XRD measurements show that these features disappear, in accordance with electrical data.

  • 37.
    Maltoni, Pierfrancesco
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Sarkar, Tapati
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Varvaro, Gaspare
    Ist Struttura Mat CNR, I-00015 Monterotondo, RM, Italy..
    Barucca, Gianni
    Univ Politecn Marche, Dept SIMAU, Via Brecce Bianche, Ancona, Italy..
    Ivanov, Sergey
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics. Moscow MV Lomonosov State Univ, Dept Chem, Leninskie Gory 1-3, Moscow 119991, Russia..
    Peddis, Davide
    Ist Struttura Mat CNR, I-00015 Monterotondo, RM, Italy.;Univ Genoa, Dipartimento Chim & Chim Ind, Via Dodecaneso 31, I-16146 Genoa, Italy..
    Mathieu, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solid State Physics.
    Towards bi-magnetic nanocomposites as permanent magnets through the optimization of the synthesis and magnetic properties of SrFe12O19 nanocrystallites2021In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 54, no 12, article id 124004Article in journal (Refereed)
    Abstract [en]

    Sol-gel synthesis was used in order to obtain nanocrystallites of the SrFe12O19 (SFO) hexaferrite in an efficient and reliable way. By optimizing the initial synthetic conditions, we were able to control the size of the nanoparticles (NPs), at lower annealing temperature. The x-ray powder diffraction, transmission electron microscopy (TEM), and magnetic measurements have demonstrated a significant relation between the morphology, size, and magnetic properties of the nanoscale SFO, revealing a definite dependence on the crystallite size along the c-axis. The obtained NPs appear almost isotropic, in the form of platelets and exhibit similar magnetic performance, in terms of the energy product (BH)(MAX), thus, demonstrating the suitability of reducing the annealing temperature without any deterioration in the magnetic properties. Additionally, this work illustrates the feasibility of the sol-gel bottom-up approach to employ magnetic NPs as building-blocks for designing hard/soft exchange-coupled bi-magnetic nanocomposites, combining the high coercivity of a hard phase (SFO) and the high saturation magnetization of a soft phase (CoFe2O4); in this regard, we discuss the tunability of the magnetic anisotropy by symbiotically restricting the growth of both phases.

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  • 38.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Invited papers from the 7th International Conference on Fine Particle Magnetism 20102010In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 43, no 47, p. 1-1Article in journal (Other academic)
  • 39.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Non-equilibrium dynamics in fine magnetic particle systems2008In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 41, no 13, p. 134011-Article in journal (Refereed)
    Abstract [en]

    Extended dynamics ( broader than Debye relaxation) occurs in fine magnetic particle systems because of the particle size distribution and the influence of interparticle interaction. In dilute negligibly interacting systems the broadening of the relaxation is governed by the effective anisotropy distribution of the particles. In dense systems, however, interparticle interaction alters the nature of the dynamics and phenomena due to correlation of the particle moments appear. The effects may at a glance only look like a change in the effective anisotropy of the individual particles. However, studies of the dynamics over several decades in observation time reveal that correlation related effects dominate the dynamics on long time scales and extend the maximum relaxation time well beyond the relaxation time of the individual particles. In addition, non-equilibrium dynamics, reminiscent of the ageing phenomenon of spin glasses, appears. Results and analyses of ac susceptibility and magnetic relaxation experiments on various fine magnetic particle systems, ranging from concentrated monodispersed ferrofluids to mechanically alloyed granular materials, are used to illustrate the cooperative nature of the dynamics.

  • 40.
    Nordlund, Michael
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Bhandary, Sumanta
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Almqvist, Nils
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Löfqvist, Torbjörn
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Grennberg, Helena
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Side-selective self-assembly of graphene and FLG on piezoelectric PVDF from suspension2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 7, article id 07LT01Article in journal (Refereed)
    Abstract [en]

    The deposition of few-layer graphene by self-assembly from suspension onto a piezoelectric polymer substrate is presented. The graphene self-assembles with negligible overlap between flakes, and with high selectivity for one of the faces of the substrate, an observation which is discussed and rationalized. A computational study on a model system further confirms the theory and supports the experimental results. The highest obtained degree of surface coverage was estimated to 77%.

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  • 41.
    Paul, Tanmoy
    et al.
    Res Inst Sustainable Energy RISE, TCG Ctr Res & Educ Sci & Technol, Sect 5, Kolkata 700091, India..
    Banerjee, Abhik
    Res Inst Sustainable Energy RISE, TCG Ctr Res & Educ Sci & Technol, Sect 5, Kolkata 700091, India..
    Das, G. P.
    Res Inst Sustainable Energy RISE, TCG Ctr Res & Educ Sci & Technol, Sect 5, Kolkata 700091, India..
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Optimizing solid electrolytes with 3d transition metal doped Li3YCl6 for Li-ion batteries2024In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 57, no 14, article id 145503Article in journal (Refereed)
    Abstract [en]

    Li3YCl6 is a promising candidate for solid electrolytes (SEs) in all-solid-state Li-ion batteries due to its high ionic conductivity, electrochemical stability, and compatibility with metal-oxide electrodes. The monoclinic and trigonal crystal structures of Li3YCl6 with space groups C2/c and P-3m1 have been studied extensively, while little attention has been given to the trigonal P-3c1 phase (space group no. 165). Additionally, Li-ion diffusion mechanism in 3d transition metal (TM) substituted compounds along with their structural stability are interesting to study. Therefore, we investigate the Li diffusion mechanism in Li3YCl6 and TM substituted Li3YCl6 in the P-3c1 phase using first-principles calculations. We have found that all the substituted compounds are thermodynamically stable at room temperature and show high oxidation stability. Li3Y0.875Co0.125Cl6 exhibits the lowest activation energy (0.11 eV) for Li-ion diffusion and the highest Li-ion mobility (σ = 0.39 mS cm−1 at room temperature), which is strongly anisotropic. We used the Crystal Orbital Hamilton Population method to analyze the bonding characteristics of Li3YCl6 and 3d TM substituted Li3YCl6 and found that the Co–Cl bond is weaker than the Cr–Cl bond. This may explain the lower activation energy observed for Li3Y0.875Co0.125Cl6. Our results provide insights into the substitution effect in Li3YCl6 superionic conductors, which could guide the design and development of high-performance SEs for Li-ion batteries.

  • 42.
    Reichel, Ludwig
    et al.
    IFW Dresden, POB 270116, D-01171 Dresden, Germany.; Tech Univ Dresden, Fac Mech Engn, Inst Mat Sci, D-01062 Dresden, Germany.
    Edström, Alexander
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pohl, Darius
    IFW Dresden, POB 270116, D-01171 Dresden, Germany.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Schultz, Ludwig
    IFW Dresden, POB 270116, D-01171 Dresden, Germany.; Tech Univ Dresden, Fac Mech Engn, Inst Mat Sci, D-01062 Dresden, Germany.
    Fähler, Sebastian
    IFW Dresden, POB 270116, D-01171 Dresden, Germany.
    On the origin of perpendicular magnetic anisotropy in strained Fe-Co(-X) films2017In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 50, no 4, article id 045003Article in journal (Refereed)
    Abstract [en]

    Very high magnetic anisotropies have been theoretically predicted for strained Fe-Co(-X) and indeed several experiments on epitaxial thin films seemed to confirm strain induced anisotropy enhancement. This study presents a critical analysis of the different contributions to perpendicular anisotropy: volume, interface and surface anisotropies. Tracing these contributions, thickness series of single layer films as well as multilayers with Au-Cu buffers/interlayers of different lattice parameters have been prepared. The analysis of their magnetic anisotropy reveals a negligible influence of the lattice parameter of the buffer. Electronic effects, originating from both, the Au-Cu interface and the film surface, outrange the elastic effects. Surface anisotropy, however, exceeds the interface anisotropy by more than a factor of three. A comparison with results from Density Functional Theory suggests, that the experimentally observed strong perpendicular surface anisotropy originates from a deviation from an ideal oxide-free surface. Accordingly, tailored Fe-Co-X/oxideinterfaces may open a route towards high anisotropy in rare-earth free materials.

  • 43.
    Roondhe, Basant
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Indian Inst Technol, Dept Met Engn & Mat Sci, Nanostruct Engn & Modeling Lab, Mumbai 400076, Maharashtra, India.
    Saha, Sankhadip
    Indian Inst Technol, Dept Met Engn & Mat Sci, Nanostruct Engn & Modeling Lab, Mumbai 400076, Maharashtra, India..
    Luo, Wei
    Uppsala Univ, Dept Phys & Astron, Mat Theory Div, Condensed Matter Theory Grp, Box 516, S-75120 Uppsala, Sweden..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Indian Inst Technol Ropar, Dept Phys, Rupnagar 140001, Punjab, India..
    Saxena, Sumit
    Indian Inst Technol, Dept Met Engn & Mat Sci, Nanostruct Engn & Modeling Lab, Mumbai 400076, Maharashtra, India..
    Detection of type-II diabetes using graphene-based biosensors2024In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 57, no 18, article id 185402Article in journal (Refereed)
    Abstract [en]

    Diabetes is a global pandemic that increases the risk of various health complications, including heart attacks, renal failure, blindness, stroke, and peripheral neuropathy. Type-2 diabetes (T2D) results from an imbalance in lipid and glucose metabolism due to hostility to insulin action and insufficient insulin production response. Valine amino acid has been identified as a potential biomarker for T2D, but there have been no rigorous studies on its interaction with branch chain amino acids. In this study, we investigated the potential of graphene/modified graphene as a valine biosensor using density functional theory to examine the electronic properties and adsorption behaviour of graphene, Si-doped graphene (SiG), and P-doped graphene (PG). The adsorption of valine over the substrates was physisorption in nature, and the adsorption energies were in the order of SiG > G > PG. Density of states (DOS) and partial DOS calculations confirmed the molecule's adsorption over the monolayers and indicated variations in the electronic properties. We also performed recovery time calculations to examine the reusability of the nano-surfaces as potential biosensors. Ultrafast recovery times were predicted for all three systems, with SiG showing the best results. Our study suggests that SiG could be used as a biosensor for valine, providing a real-time and efficient diagnostic tool for T2D.

  • 44.
    Rubino, Stefano
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Schattschneider, Peter
    Inst. für Festkörperphysik und Univ. Serviceeinrichtung für Elektronenmikroskopie, Technische Universität Wien,Vienna, Austria.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Verbeeck, Johan
    EMAT, University of Antwerp, Antwerpen, Belgium.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Simulation of magnetic circular dichroism in the electron microscope2010In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 43, no 47, p. 474005-Article in journal (Refereed)
    Abstract [en]

    As electron energy-loss spectroscopy (EELS) and x-ray absorption spectroscopy (XAS) probe the same transitions from core–shell states to unoccupied states above the Fermi energy, it should always be possible to apply the two techniques to the same physical phenomena, such as magnetic dichroism, and obtain the same information. Indeed, the similarity in the expression of the electron and x-ray cross-sections had been already exploited to prove the equivalence of x-ray magnetic linear dichroism and anisotropy in EELS, by noting that the polarization vector of a photon plays the same role as the momentum transfer in electron scattering. Recently, the same was proven true for x-ray magnetic circular dichroism (XMCD) by establishing a new TEM technique called EMCD (electron energy-loss magnetic chiral dichroism) (Schattschneider P et al 2006 Nature 441 486–8), which makes use of special electron scattering conditions to force the absorption of a circularly polarized virtual photon.The intrinsic advantage of EMCD over XMCD is the high spatial resolution of electron microscopes, which are readily available. Among the particular obstacles in EMCD that do not exist for synchrotron radiation, is the notoriously low signal and the very particular scattering conditions necessary to observe a chiral dichroic signal. In spite of that, impressive progress has been made in recent years. The signal strength could be considerably increased, and some innovations such as using a convergent beam have been introduced. EMCD has evolved into several techniques, which make full use of the versatility of the TEM and energy filtering, spectroscopy or STEM conditions (Rubino S 2007 Magnetic circular dichroism in the transmission electron microscope PhD Thesis Vienna University of Technology, Vienna, Austria).

  • 45.
    Sarkar, Tapati
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ivanov, Sergey A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Bazuev, G. V.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mathieu, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Successive phase transitions in the orthovanadate TmVO32015In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 48, no 34, article id 345003Article in journal (Refereed)
    Abstract [en]

    Synthesis and crystal structure, magnetization and heat capacity measurements of phase pure polycrystalline TmVO3 are reported. TmVO3 was stabilized in the orthorhombic structure by thermal treatment of the precursor TmVO4 in a reducing atmosphere. Magnetization and heat capacity measurements reveal the presence of several successive structural and magnetic phase transitions in this compound. At T = 108 K, the sample undergoes a transition from a paramagnetic state to an antiferromagnetic state, followed by a second transition at 78 K which is related to spin and orbital reorientation. The heat capacity measurements reveal the presence of a third transition in the paramagnetic state (at T = 175 K), which corresponds to a structural phase transition and orbital ordering. At low temperatures (similar to 15 K) and weak fields, there is an anomaly in the magnetization, which may be associated with antiferromagnetic short range ordering of the Tm3+ ions.

  • 46.
    Schröter, M.
    et al.
    Univ Duisburg Essen, Fac Phys, D-47048 Duisburg, Germany.;Univ Duisburg Essen, Ctr Nanointegrat Duisburg Essen CENIDE, D-47048 Duisburg, Germany..
    Herper, Heike C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grünebohm, A.
    Ruhr Univ Bochum, Interdisciplinary Ctr Adv Mat Simulat ICAMS, D-44780 Bochum, Germany..
    Tuning the magnetic phase diagram of Ni-Mn-Ga by Cr and Co substitution2022In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 55, no 2, article id 025002Article in journal (Refereed)
    Abstract [en]

    Ni-Mn-based Heusler alloys have a high technical potential related to a large change of magnetization at the structural phase transition. These alloys show a subtle dependence of magnetic properties and structural phase stability on composition and substitution by 3d elements and although they have been extensively investigated, there are still ambiguities in the published results and their interpretation. To shed light on the large spread of reported properties, we perform a comprehensive study by means of density functional theory calculations. We focus on Cr and Co co-substitution whose benefit has been predicted previously for the expensive Ni-Mn-In-based alloy and study the more abundant iso-electronic counterpart Ni-Mn-Ga. We observe that substituting Ni partially by Co and/or Cr enhances the magnetization of the Heusler alloy and at the same time reduces the structural transition temperature. Thereby, Cr turns out to be more efficient to stabilize the ferromagnetic alignment of the Mn spins by strong antiferromagnetic interactions between Mn and Cr atoms. In a second step, we study Cr on the other sublattices and observe that an increase in the structural transition temperature is possible, but depends critically on the short-range order of Mn and Cr atoms. Based on our results, we are able to estimate composition dependent magnetic phase diagrams. In particular, we demonstrate that neither the atomic configuration with the lowest energy nor the results based on the coherent potential approximation are representative for materials with a homogeneous distribution of atoms and we also predict a simple method for fast screening of different concentrations which can be viewed as a blueprint for the study of high entropy alloys. Our results help to explain the large variation of experimentally found materials properties.

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  • 47.
    Schöldström, Jens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Zimmermann, Uwe
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Determination of the optical constants for Cu(In,Ga)Se2 and CuxSe in the IR region2012In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, no 11, p. 115101-Article in journal (Refereed)
    Abstract [en]

    The complex refractive index of CuxSe and Cu(In,Ga)Se2 has been calculated from experimental data in the wavelength region from 0.3 to 20μm. For Cu(In,Ga)Se2, the imaginary part exhibits very low values in the infrared range, whereas the real part decreases gently from 3 to 2.5. The CuxSe film is found to be conducting with increasing real and imaginary parts. It is found not to follow the Drude model. Reflectance and transmittance measurements were performed on thin films grown on soda lime glass and double polished low-doped silicon as substrates. Solutions for the complex refractive index were extracted from the measurement data using an optical model for the film and substrate. A method to map all solutions for the complex refractive index was applied to select the physically correct one.

  • 48.
    Segev, Gideon
    et al.
    Tel Aviv Univ, Fac Engn, Dept Phys Elect, Tel Aviv, Israel..
    Kibsgaard, Jakob
    Tech Univ Denmark, Dept Phys, DK-2800 Lyngby, Denmark..
    Hahn, Christopher
    Lawrence Livermore Natl Lab, Mat Sci Div, Livermore, CA 94550 USA..
    Xu, Zhichuan J.
    Nanyang Technol Univ, Sch Mat Sci & Engn, Singapore, Singapore..
    Cheng, Wen-Hui (Sophia)
    Natl Cheng Kung Univ, Dept Mat Sci & Technol, Tainan 701, Taiwan..
    Deutsch, Todd G.
    Natl Renewable Energy Lab, 15013 Denver West Pkwy, Golden, CO 80401 USA..
    Xiang, Chengxiang
    CALTECH, Dept Appl Phys & Mat Sci, Pasadena, CA 91125 USA..
    Zhang, Jenny Z.
    Univ Cambridge, Yusuf Hamied Dept Chem, Lensfield Rd, Cambridge CB2 1EW, England..
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Nocera, Daniel G.
    Harvard Univ, Dept Chem & Chem Biol, 12 Oxford St, Cambridge, MA 02138 USA..
    Weber, Adam Z.
    Lawrence Berkeley Natl Lab, Energy Technol Area, Energy Convers Grp, Berkeley, CA 94720 USA..
    Agbo, Peter
    Lawrence Berkeley Natl Lab, Chem Sci Div, Berkeley, CA 94720 USA..
    Hisatomi, Takashi
    Shinshu Univ, Interdisciplinary Cluster Cutting Edge Res, Res Initiat Supra Mat, 4-17-1 Wakasato, Nagano, Nagano 3808553, Japan.;JST PRESTO, 4-17-1 Wakasato, Nagano, Nagano 3808553, Japan..
    Osterloh, Frank E.
    Univ Calif Davis, Dept Chem, Davis, CA 95616 USA..
    Domen, Kazunari
    Shinshu Univ, Interdisciplinary Cluster Cutting Edge Res, Res Initiat Supra Mat, 4-17-1 Wakasato, Nagano, Nagano 3808553, Japan.;Univ Tokyo, Off Univ Prof, Bunkyo Ku, 2-11-16 Yayoi, Tokyo 1138656, Japan..
    Abdi, Fatwa F.
    Helmholtz Zentrum Berlin Mat & Energie GmbH, Inst Solar Fuels, Hahn Meitner Pl 1, D-14109 Berlin, Germany..
    Haussener, Sophia
    Ecole Polytech Fed Lausanne EPFL, Lab Renewable Energy Sci & Engn, Stn 9, CH-1015 Lausanne, Switzerland..
    Miller, Daniel J.
    Lawrence Berkeley Natl Lab, Chem Sci Div, Berkeley, CA 94720 USA..
    Ardo, Shane
    Univ Calif Irvine, Dept Chem, Dept Chem & Biomol Engn, Dept Mat Sci & Engn, Irvine, CA 92697 USA..
    McIntyre, Paul C.
    Stanford Univ, Dept Mat Sci & Engn, Stanford, CA 94305 USA..
    Hannappel, Thomas
    Tech Univ Ilmenau, Inst Phys, Fundamentals Energy Mat, D-98693 Ilmenau, Thuringia, Germany..
    Hu, Shu
    Yale Univ, Dept Chem & Environm Engn, New Haven, CT 06520 USA..
    Atwater, Harry
    CALTECH, Thomas J Watson Lab Appl Phys, Pasadena, CA 91125 USA..
    Gregoire, John M.
    CALTECH, Div Engn & Appl Sci, Pasadena, CA 91024 USA..
    Ertem, Mehmed Z.
    CALTECH, Liquid Sunlight Alliance, Pasadena, CA 91024 USA.;Brookhaven Natl Lab, Chem Div, Upton, NY 11973 USA..
    Sharp, Ian D.
    Tech Univ Munich, Walter Schottky Inst, D-85748 Garching, Germany.;Tech Univ Munich, Phys Dept, D-85748 Garching, Germany..
    Choi, Kyoung-Shin
    Univ Wisconsin, Dept Chem, Madison, WI 53706 USA..
    Lee, Jae Sung
    Ulsan Natl Inst Sci & Technol UNIST, Sch Energy & Chem Engn, Dept Energy Engn, Ulsan 44919, South Korea..
    Ishitani, Osamu
    Tokyo Inst Technol, Dept Chem, Meguro Ku, 2-12-1-NE-1 Ookayama, Tokyo, Japan..
    Ager, Joel W.
    Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA.;Univ Calif Berkeley, Dept Mat Sci & Engn, Berkeley, CA 94720 USA..
    Prabhakar, Rajiv Ramanujam
    Lawrence Berkeley Natl Lab, Chem Sci Div, Berkeley, CA 94720 USA..
    Bell, Alexis T.
    Lawrence Berkeley Natl Lab, Chem Sci Div, Berkeley, CA 94720 USA.;Univ Calif Berkeley, Dept Chem & Biomol Engn, Berkeley, CA 94720 USA..
    Boettcher, Shannon W.
    Univ Oregon, Dept Chem & Biochem, Eugene, OR 97403 USA.;Univ Oregon, Oregon Ctr Electrochem, Eugene, OR 97403 USA..
    Vincent, Kylie
    Univ Oxford, Dept Chem, Inorgan Chem Lab, South Parks Rd, Oxford OX1 3QR, England..
    Takanabe, Kazuhiro
    Univ Tokyo, Sch Engn, Dept Chem Syst Engn, Bunkyo Ku, 7-3-1 Hongo, Tokyo 1138656, Japan..
    Artero, Vincent
    Univ Grenoble Alpes, Lab Chim & Biol Metaux, IRIG, CNRS,CEA, 17 Rue Martyrs, F-38054 Grenoble, France..
    Napier, Ryan
    Leiden Univ, Leiden Inst Chem, POB 9502, NL-2300 RA Leiden, Netherlands..
    Cuenya, Beatriz Roldan
    Max Planck Gesell, Dept Interface Sci, Fritz Haber Inst, Faradayweg 4-6, D-14195 Berlin, Germany..
    Koper, Marc T. M.
    Leiden Univ, Leiden Inst Chem, POB 9502, NL-2300 RA Leiden, Netherlands..
    Van de Krol, Roel
    Helmholtz Zentrum Berlin Mat & Energie GmbH, Inst Solar Fuels, Hahn Meitner Pl 1, D-14109 Berlin, Germany.;Tech Univ Berlin, Inst Chem, Str 17 Juni 124, D-10623 Berlin, Germany..
    Houle, Frances
    Lawrence Berkeley Natl Lab, Chem Sci Div, Berkeley, CA 94720 USA..
    The 2022 solar fuels roadmap2022In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 55, no 32, article id 323003Article in journal (Refereed)
    Abstract [en]

    Renewable fuel generation is essential for a low carbon footprint economy. Thus, over the last five decades, a significant effort has been dedicated towards increasing the performance of solar fuels generating devices. Specifically, the solar to hydrogen efficiency of photoelectrochemical cells has progressed steadily towards its fundamental limit, and the faradaic efficiency towards valuable products in CO2 reduction systems has increased dramatically. However, there are still numerous scientific and engineering challenges that must be overcame in order to turn solar fuels into a viable technology. At the electrode and device level, the conversion efficiency, stability and products selectivity must be increased significantly. Meanwhile, these performance metrics must be maintained when scaling up devices and systems while maintaining an acceptable cost and carbon footprint. This roadmap surveys different aspects of this endeavor: system benchmarking, device scaling, various approaches for photoelectrodes design, materials discovery, and catalysis. Each of the sections in the roadmap focuses on a single topic, discussing the state of the art, the key challenges and advancements required to meet them. The roadmap can be used as a guide for researchers and funding agencies highlighting the most pressing needs of the field.

    Download full text (pdf)
    fulltext
  • 49.
    Shayestehaminzadeh, Seyedmohammad
    et al.
    Univ Iceland, Inst Sci, Dunhaga 3, IS-107 Reykjavik, Iceland.;Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Thorsteinsson, Einar B.
    Univ Iceland, Inst Sci, Dunhaga 3, IS-107 Reykjavik, Iceland..
    Primetzhofer, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Magnus, Fridrik
    Univ Iceland, Inst Sci, Dunhaga 3, IS-107 Reykjavik, Iceland..
    Olafsson, Sveinn
    Univ Iceland, Inst Sci, Dunhaga 3, IS-107 Reykjavik, Iceland..
    Epitaxial and textured TiN thin films grown on MgO(100) by reactive HiPIMS: the impact of charging on epitaxial to textured growth crossover2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 45, article id 455301Article in journal (Refereed)
    Abstract [en]

    Ultra-thin TiN films were grown on MgO(100) substrates by high power impulse magnetron sputtering at growth temperatures of 35 degrees C-400 degrees C. Epitaxial TiN films were obtained when a metallic substrate holder is used, while only textured films were achieved for the films grown by HiPIMS using a substrate holder with a ceramic shadow mask. For the entire range of growth temperatures, the epitaxial films are denser and exhibit a higher growth rate compared to the textured films. Also, chemical composition analysis reveals that all the epitaxial TiN films are N-deficient sub-stoichiometric. As the growth temperature increases, the surface roughness of both epitaxial and textured films decreases, however the epitaxial films generally show less roughness than the textured films. In comparison to epitaxial films previously grown by dc magnetron sputtering, the HiPIMS grown epitaxial films are sub-stoichiometric and according to x-ray measurements, they are in a higher strain state whilst presenting higher film density and atomically smoother surfaces. A HiPIMS-induced negative charging of the TiN islands formed on top of the insulating mask is concluded to be the main reason for the growth mode transition from two dimensional Stranski-Krastanov to three dimensional Volmer-Weber when the shadow mask is used. Acceleration of the ionized species of the HiPIMS plasma including Ti+, N+, and Ti2+ toward the substrate when they approach the substrate holder is the reason for the observed changes in the film densities, growth rates, and surface roughness.

  • 50.
    Sisman, Altug
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Aydin, Alhun
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Istanbul Technical University, Energy Institute; The Hebrew University of Jerusalem.
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thermoshape effect for energy harvesting with nanostructures2020In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 53, no 37, article id 375501Article in journal (Refereed)
    Abstract [en]

    We propose a mechanism for nanoscale energy conversion, an electric voltage induced by a temperature gradient in a junction composed of the same material having exactly the same geometric sizes, but distinct shapes. The proposed effect appears as a result of only temperature and shape difference, hence it is called thermoshape effect. For GaAs quantum confined semiconductor nanostructures, we first introduce the existence of quantum shape effects on thermoelectric transport coefficients at ballistic regime. We show that the shape alone enters as a control parameter on transport properties of confined nanostructures. The thermoshape voltage is then calculated by using the Landauer formalism. Our calculations show that the thermoshape voltage has a constant value in the order of mV K−1 for the variation of chemical potential in non-degenerate regime and it decreases rapidly after entering weakly degenerate regime where it oscillates around zero within plus/minus 10 µV K−1 magnitude. A persistent voltage range may pave the way for easier experimental demonstration of the effect. Our work explicitly shows how important the effect of overall geometry is in nanoscale thermoelectric materials, and can be utilized even if all sizes are the same. A thermoshape junction not only represents a viable setup for the macroscopic manifestation of quantum shape effects, but also constitutes their first possible device application.

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