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  • 1. Akansel, Serkan
    et al.
    Venugopal, Vijayaharan A.
    Kumar, Ankit
    Gupta, Rahul
    Brucas, Rimantas
    George, Sebastian
    Neagu, Alexandra
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gubbins, Mark
    Andersson, Gabriella
    Svedlindh, Peter
    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 8.0 x 10(-3) and 4.5 x 10(-3) were obtained from in-plane and out-of-plane measurements, respectively, for the as prepared samples, values that were reduced to about 6.5 x 10(-3) and 4.0 x 10(-3) for annealed samples.

  • 2.
    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.

  • 3.
    Alami, J.
    et al.
    Sulzer Metaplas GmbH, Germany.
    Sarakinos, Kostas
    Institute of Physics (IA), RWTH Aachen University, Germany.
    Uslu, F.
    RWTH Aachen University, Germany.
    Klever, C.
    RWTH Aachen University, Germany.
    Dukwen, J.
    RWTH Aachen University, Germany.
    Wuttig, M.
    RWTH Aachen University, Germany.
    On the phase formation of titanium oxide films grown by reactive high power pulsed magnetron sputtering2009In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 42, no 11, p. 115204-Article in journal (Refereed)
    Abstract [en]

    High power pulsed magnetron sputtering is used for the growth of titanium dioxide (TiO(2)) films at different working pressures and orientations of the substrate with respect to the target surface. In the case of substrates oriented parallel to the target surface, the increase in the working pressure from 0.5 to 3 Pa results in the growth of crystalline TiO(2) films with phase compositions ranging from rutile to anatase/rutile mixtures. When depositions are performed on substrates placed perpendicularly to the target surface, rutile films that consist of TiO(2) nanocrystals embedded in an amorphous matrix are obtained at 0.5 Pa. Increase in the working pressure leads to the deposition of amorphous films. These findings are discussed in the light of the energetic bombardment provided to the growing film at the various deposition conditions.

  • 4.
    Alami, J.
    et al.
    University of Aachen, Germany.
    Sarakinos, Kostas
    Institute of Physics (IA), RWTH Aachen University, Germany.
    Uslu, F.
    University of Aachen, Germany.
    Wuttig, M.
    University of Aachen, Germany.
    On the relationship between the peak target current and the morphology of chromium nitride thin films deposited by reactive high power pulsed magnetron sputtering2009In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 42, no 1, p. 015304-Article in journal (Refereed)
    Abstract [en]

    High power pulsed magnetron sputtering (HPPMS) is used to deposit CrN films without external heating at different peak target currents, while the average current is kept constant. Films are also grown by dc magnetron sputtering (dcMS), for reference. The plasma properties, the deposition rate and the morphology of the films are investigated. The plasma analysis reveals that HPPMS provides higher fluxes of ionized species (both gas and sputtered) to the growing film, as compared with dcMS. In addition, the ionic bombardment during HPPMS increases, when the peak target current is increased. The HPPMS films exhibit changes of the density and the surface roughness as the peak target current increased, while the deposition rate decreases drastically. Furthermore, it is found that different thin-film morphologies are obtained starting from a porous columnar morphology for the dcMS films, which turns to a dense columnar one at low peak target currents and ends up to a featureless morphology at high peak target currents for the films grown by HPPMS. A new structure zone model specific for high ionization sputtering is, therefore, outlined.

  • 5.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Shock wave generation in laser ablation studied using pulsed digital holographic interferometry2008In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 41, no 21Article in journal (Refereed)
    Abstract [en]

    Pulsed digital holographic interferometry has been used to study the shock wave induced by a Q-switched Nd-YAG laser (λ = 1064 nm and pulse duration 12 ns) on a polycrystalline boron nitride (PCBN) ceramic target under atmospheric air pressure. A special setup based on using two synchronized wavelengths from the same laser for processing and measurement simultaneously has been introduced. Collimated laser light (λ = 532 nm) passed through the volume along the target and digital holograms were recorded for different time delays after processing starts. Numerical data of the integrated refractive index field were calculated and presented as phase maps showing the propagation of the shock wave generated by the process. The location of the induced shock wave front was observed for different focusing and time delays. The amount of released energy, i.e. the part of the incident energy of the laser pulse that is eventually converted to a shock wave has been estimated using the point explosion model. The released energy is normalized by the incident laser pulse energy and the energy conversion efficiency between the laser pulse and PCBN target has been calculated at different power densities. The results show that the energy conversion efficiency seems to be constant around 80% at high power densities.

  • 6.
    Aminlashgari, Nina
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. ABB, Sweden.
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. ABB, Sweden.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Characterization of degradation fragments released by arc-induced ablation of polymers in air2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 5, article id 055502Article in journal (Refereed)
    Abstract [en]

    Polymers exposed to high intensity arc plasmas release material in a process called arc-induced ablation. In order to investigate the degradation fragments released due to this process, two different polymeric materials, poly(oxymethylene) copolymer (POM-C) and poly(methyl methacrylate) (PMMA), were exposed to a transient, high-power arc plasma in air. A small fraction of the ablated material drifting away from the arcing volume was deposited on a fixed glass substrate during the total duration of a 2 kA ac current semicycle. In addition, another fraction of the released material was deposited on a second moving substrate to obtain a time-resolved streak 'image' of the arc-induced ablation process. For the first time, mass spectra of degradation fragments produced by arc-induced ablation were obtained from the material deposited on the substrates by using laser desorption ionization time-of-flight mass spectrometry (LDI-ToF-MS). It was found that oligomers with mean molecular weight ranging between 400 and 600 Da were released from the surface of the studied polymers. The obtained spectra suggest that the detected degradation fragments of POM could be released by random chain scission of the polymer backbone. In turn, random chain scission and splitting-off the side groups are suggested as the main chemical mechanism leading to the release of PMMA fragments under arc-induced ablation.

  • 7.
    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)
  • 8.
    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.

  • 9.
    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)
  • 10.
    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.

  • 11. Azarov, A. Yu
    et al.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Svensson, B. G.
    Kuznetsov, A. Yu
    Annealing of ion implanted CdZnO2012In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, no 23, p. 235304-Article in journal (Refereed)
    Abstract [en]

    We have studied the effect of the Cd content on the recovery of ion-induced damage in wurtzite CdxZn1-xO (x <= 0.05) films and compared with that in pure wurtzite ZnO and rock-salt CdO.200 keV Au+ and 55 keV Ar+ ion implants were performed at room temperature in the dose range of 5 x 1014-6.5 x 1015 cm-2. Rutherford backscattering/channelling spectrometry was used to characterize the damage evolution in the course of annealing (600-900 degrees C in air). A complex defect annealing behaviour is revealed in CdZnO as a function of annealing temperature, Cd content and ion dose. In particular, defects in the low dose implanted CdZnO films can be effectively removed at 800 degrees C, while the high dose implantation results in the formation of defects stable at least up to 900 degrees C. Moreover, annealing of the CdZnO films is accompanied by Cd loss at the surface for temperatures exceeding 800 degrees C. In contrast, CdO exhibits a typical damage accumulation behaviour for metals and semiconductors with high degree of ionicity, resulting in saturation and extended defect formation at high ion doses. These extended defects in pure ZnO and CdO, formed either directly during implantation or by reconstruction during post-implant annealing, are substantially more stable compared with small defects which can be efficiently removed at 700 degrees C and 600 degrees C for ZnO and CdO, respectively.

  • 12.
    Becerra Garcia, Marley
    et al.
    Division for Electricity, Uppsala University.
    Cooray, Vernon
    Division for Electricity, Uppsala University.
    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 8Article in journal (Refereed)
    Abstract [en]

    The early emission of streamers in laboratory long air gaps under switching impulses has beenobserved to reduce the time of initiation of leader positive discharges. This fact has beenarbitrarily extrapolated by the manufacturers of early streamer emission devices to the case ofupward connecting leaders initiated under natural lightning conditions, in support of thosenon-conventional terminals that claim to perform better than Franklin lightning rods. In orderto discuss the physical basis and validity of these claims, a self-consistent model based on thephysics of leader discharges is used to simulate the performance of lightning rods in thelaboratory and under natural lightning conditions. It is theoretically shown that the initiation ofearly streamers can indeed lead to the early initiation of self-propagating positive leaders inlaboratory long air gaps under switching voltages. However, this is not the case for positiveconnecting leaders initiated from the same lightning rod under the influence of the electricfield produced by a downward moving stepped leader. The time evolution of the developmentof positive leaders under natural conditions is different from the case in the laboratory, wherethe leader inception condition is closely dependent upon the initiation of the first streamerburst. Our study shows that the claimed similarity between the performance of lightning rodsunder switching electric fields applied in the laboratory and under the electric field producedby a descending stepped leader is not justified. Thus, the use of existing laboratory results tovalidate the performance of the early streamer lightning rods under natural conditions is not justified.

  • 13.
    Becerra Garcia, Marley
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Pettersson, Jonas
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Optical radiative properties of ablating polymers exposed to high-power arc plasmas2018In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 12, article id 125202Article in journal (Refereed)
    Abstract [en]

    The radiative properties of polymers exposed to high-intensity radiation are of importance for the numerical simulation of arc-induced ablation. The paper investigates the optical properties of polymethylmethacrylate PMMA and polyamide PA6 films exposed to high-power arc plasmas, which can cause ablation of the material. A four-flux radiative approximation is first used to estimate absorption and scattering coefficients of the tested materials in the ultraviolet (UV) and in the visible (VIS) ranges from spectrophotometric measurements. The temperature-induced variation of the collimated transmissivity of the polymers is also measured from room temperature to the glass temperature of PMMA and the melting temperature of PA6. Furthermore, band-averaged absorption and scattering coefficients of non-ablating and ablating polymers are estimated from the UV to the short-wavelength infrared (SWIR), covering the range of interest for the simulation of arc-induced ablation. These estimates are obtained from collimated transmissivities measured with an additional in situ photometric system that uses a high-power, transient arc plasma to both illuminate the samples and to induce ablation. It is shown that the increase in the bulk temperature of PA6 leads to a strong reversible increase in collimated transmissivity, significantly reducing the absorption and scattering coefficients of the material. A weaker but opposite effect of temperature on the optical properties is found in PMMA. As a consequence, it is suggested that the absorption coefficient of polymers used for arc-induced ablation estimates should not be taken directly from direct collimated transmissivity measurements at room temperature. The band-averaged radiation measurements also show that the layer of products released by ablation of PMMA produces scattering radiation losses mainly in the VIS-SWIR ranges, which are only a small fraction of the total incident arc radiation. In a similar manner, the ablation layer of PA6 leads to weak absorption radiation losses, although mainly in the UV range.

  • 14.
    Becerra Garcia, Marley
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, S-10044 Stockholm, Sweden.;ABB Corp Res, S-72226 Vasteras, Sweden..
    Pettersson, Jonas
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Franke, Steffen
    INP Leibniz Inst Plasma Sci & Technol, D-17489 Greifswald, Germany..
    Gortschakow, Sergey
    INP Leibniz Inst Plasma Sci & Technol, D-17489 Greifswald, Germany..
    Temperature and pressure profiles of an ablation-controlled arc plasma in air2019In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 52, no 43, article id 434003Article in journal (Refereed)
    Abstract [en]

    Experimental measurements of the spatial distribution of temperature and composition of ablation-controlled arc plasmas are a key to validate the predictions of metal evaporation and polymer ablation models. Thus, high-speed photography and space-resolved spectroscopic measurements have been performed to characterize a stable air arc plasma jet controlled by ablation of a polymer nozzle made of Polyoxymethylene copolymer (POM-C) or polyamide (PA6). The spectroscopic analysis is performed along a plane perpendicular to the arc jet axis for a current of 1.8 kA, corresponding to an estimated current density of similar to 65 A mm(-2). Temperature and partial pressure profiles of the plasma for copper, hydrogen and carbon in the gas mixture are estimated as an inverse optimization problem by using measured side-on radiance spectra and radiative transfer spectral simulations. It is shown that the generated ablation-controlled arc has a complicated, non-uniform gas composition. Thus, the generated arc jet has a thin metallic core with a lower almost constant hydrogen pressure, surrounded by a thicker hydrogen and carbon mantle at partial pressures slightly lower than atmospheric pressure. The separation of hydrogen and carbon in the core is a consequence of demixing of the polymer vapour in the plasma. It is found that the overall shape of the temperature and pressure profiles obtained for the arc plasmas with the POM-C and PA6 nozzles are similar although differ in peak values and width.

  • 15.
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Glow corona generation and streamer inception at the tip of grounded objects during thunderstorms: revisited2013In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 46, no 13, p. 135205-Article in journal (Refereed)
    Abstract [en]

    The initiation of streamers prior to a lightning strike can be reportedly inhibited by glow corona discharges generated from tall objects. In contrast to previous studies based on a simplified one-dimensional model of glow corona, a two-dimensional evaluation of the corona ion drift from tall objects is used here to analyse this effect quantitatively. Proper estimates for the corona space charge distribution generated during both the charging process of a thundercloud and the descent of the downward stepped leader are thus calculated. It is found that the shielding effect of the corona space charge on the streamer inception is not as severe as previously reported. Estimations of the effective height of the downward leader tip at which streamer inception takes place are presented and discussed for lightning rods and dissipation array systems.

  • 16.
    Becerra, Marley
    et al.
    Division for Electricity, Uppsala University.
    Cooray, Vernon
    Division for Electricity, Uppsala University.
    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 movingconnecting leader in the presence of a downward moving lightning steppedleader is a must in the determination of the lateral attraction distance of alightning 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. Theleader 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 thepositive connecting leaders from its inception to the final connection withthe 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-consistentlyobtained. The obtained results are compared with an altitude triggeredlightning experiment and there is good agreement between the modelpredictions and the measured leader current and the experimentally inferredspatial and temporal location of the final jump. It is also found that the usualassumption of constant charge per unit length, based on laboratoryexperiments, is not valid for lightning upward connecting leaders.

  • 17.
    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.

  • 18.
    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.

  • 19.
    Becerra, Marley
    et al.
    Division for Electricity, Uppsala University.
    Cooray, Vernon
    Division for Electricity, Uppsala University.
    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 andaborted 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 byusing 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 theinception 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 alsocompared with the existing leader inception models and discussed.

  • 20.
    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.

  • 21.
    Ben Sedrine, Nabiha
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. University of Aveiro, Portugal; University of Aveiro, Portugal.
    Zukauskaite, Agne
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Fraunhofer Institute Appl Solid State Phys, Germany.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Jensen, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Schoeche, S.
    University of Nebraska, NE 68588 USA.
    Schubert, M.
    University of Nebraska, NE 68588 USA.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Infrared dielectric functions and optical phonons of wurtzite YxAl1-xN (0 less than= x less than= 0.22)2015In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 48, no 41, p. 415102-Article in journal (Refereed)
    Abstract [en]

    YAlN is a new member of the group-III nitride family with potential for applications in next generation piezoelectric and light emitting devices. We report the infrared dielectric functions and optical phonons of wurtzite (0001) YxAl1-xN epitaxial films with 0 less than= x less than= 0.22. The films are grown by magnetron sputtering epitaxy on c-plane Al2O3 and their phonon properties are investigated using infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The infrared-active E-1(TO) and LO, and the Raman active E-2 phonons are found to exhibit one-mode behavior, which is discussed in the framework of the MREI model. The compositional dependencies of the E-1(TO), E-2 and LO phonon frequencies, the high-frequency limit of the dielectric constant, epsilon(infinity), the static dielectric constant, epsilon(0), and the Born effective charge Z(B) are established and discussed.

  • 22.
    Beyer, Franziska
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Isoya, J
    University of Tsukuba, Japan .
    Morishita, N
    Japan Atom Energy Agency, Japan .
    Ohshima, T
    University of Tsukuba, Japan .
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Capacitance transient study of a bistable deep level in e(-)-irradiated n-type 4H-SiC2012In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, no 45Article in journal (Refereed)
    Abstract [en]

    Using capacitance transient techniques, a bistable centre, called FB centre here, was observed in electron irradiated 4H-SiC. In configuration A, the deep level known as EH5 (E-a = E-C - 1.07 eV) is detected in the deep level transient spectroscopy spectrum, whereas for configuration B no obvious deep level is observed in the accessible part of the band gap. Isochronal annealing revealed the transition temperatures to be T-A -andgt; B andgt; 730K and for the opposite process T-B -andgt; A approximate to 710 K. The energy needed to conduct the transformations were determined to be E-A(A -andgt; B) = (2.1 +/- 0.1) eV and E-A(B -andgt; A) = (2.3 +/- 0.1) eV, respectively. The pre-factor indicated an atomic jump process for the opposite transition A -andgt; B and a charge carrier-emission dominated process in the case of B -andgt; A. Minority charge carrier injection enhanced the transformation from configuration B to configuration A by lowering the transition barrier by about 1.4 eV. Since the bistable FB centre is already present after low-energy electron irradiation (200 keV), it is likely related to carbon.

  • 23. Borg, Karl
    et al.
    Söderholm, Lars H.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Thermophoretic motion of bodies with axial symmetry2007In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 40, no 1, p. 148-155Article in journal (Refereed)
    Abstract [en]

    Thermophoresis of axially symmetric bodies is investigated to first order in the Knudsen number, Kn. The study is made in the limit where the typical length of the immersed body is small compared with the mean free path. It is shown that in this case, in contrast to what is the case for spherical bodies, the arising thermal force on the body is not in general anti-parallel to the temperature gradient. It is also shown that the gas exerts a torque on the body, which in magnitude and direction depends on the body geometry. Equations of motion describing the body movement are derived. Stationary solutions are studied.

  • 24.
    Brenning, Nils
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lundin, Daniel
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Minea, T.
    Costin, C.
    Vitelaru, C.
    Spokes and charged particle transport in HiPIMS magnetrons2013In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 46, no 8, p. 084005-Article in journal (Refereed)
    Abstract [en]

    Two separate scientific communities are shown to have studied one common phenomenon, azimuthally rotating dense plasma structures, also called spokes, in pulsed-power E x B discharges, starting from quite different approaches. The first body of work is motivated by fundamental plasma science and concerns a phenomenon called the critical ionization velocity, CIV, while the other body of work is motivated by the applied plasma science of high power impulse magnetron sputtering (HiPIMS). Here we make use of this situation by applying experimental observations, and theoretical analysis, from the CIV literature to HiPIMS discharges. For a practical example, we take data from observed spokes in HiPIMS discharges and focus on their role in charged particle transport, and in electron energization. We also touch upon the closely related questions of how they channel the cross-B discharge current, how they maintain their internal potential structure and how they influence the energy spectrum of the ions? New particle-in-cell Monte Carlo collisional simulations that shed light on the azimuthal drift and expansion of the spokes are also presented.

  • 25.
    Cemin, Felipe
    et al.
    Univ Paris Saclay, France.
    Tsukamoto, Makoto
    Tokyo Metropolitan Univ, Japan.
    Keraudy, Julien
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    Antunes, Vinicius Gabriel
    Univ Estadual Campinas, Brazil.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    Alvarez, Fernando
    Univ Estadual Campinas, Brazil.
    Minea, Tiberiu
    Univ Paris Saclay, France.
    Lundin, Daniel
    Univ Paris Saclay, France.
    Low-energy ion irradiation in HiPIMS to enable anataseTiO(2) selective growth2018In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 23, article id 2353011Article in journal (Refereed)
    Abstract [en]

    High power impulse magnetron sputtering (HiPIMS) has already demonstrated great potential for synthesizing the high-energy crystalline phase of titanium dioxide (rutile Ti-O2) due to large quantities of highly energetic ions present in the discharge. In this work, it is shown that the metastable anatase phase can also be obtained by HiPIMS. The required deposition conditions have been identified by systematically studying the phase formation, microstructure and chemical composition as a function of mode of target operation as well as of substrate temperature, working pressure, and peak current density. It is found that films deposited in the metal and transition modes are predominantly amorphous and contain substoichiometric TiOx compounds, while in compound mode they are well-crystallized and present only O2- ions bound to Ti4+, i.e. pure TiO2. Anatase TiO2 films are obtained for working pressures between 1 and 2 Pa, a peak current density of similar to 1 A cm(-2) and deposition temperatures lower than 300 degrees C. Rutile is favored at lower pressures (amp;lt; 1 Pa) and higher peak current densities (amp;gt;2 A cm(-2)), while amorphous films are obtained at higher pressures (greater than or similar to 5 Pa). Microstructural characterization of selected films is also presented.

  • 26.
    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.

  • 27.
    Choquet, Isabelle
    et al.
    University West, Department of Engineering Science.
    Javidi Shirvan, Alireza
    University West, Department of Engineering Science, Division of Production Engineering.
    Nilsson, Håkan
    Chalmers University of Technology, Department of Applied Mechanics,412 96 Gothenburg, Sweden.
    On the choice of electromagnetic model for shorthigh-intensity arcs, applied to welding2012In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, no 20, p. 205203-Article in journal (Refereed)
    Abstract [en]

    Four different approaches were considered for modelling the electromagneticfields of high-intensity electric arcs: i) the three-dimensional model, ii) the twodimensionalaxi-symmetric model, iii) the electric potential formulation, and iv) themagnetic field formulation. The underlying assumptions and the differences betweenthese models are described in detail. Models i) to iii) reduce to the same limit for anaxi-symmetric configuration with negligible radial current density, contrary to modeliv). Models i) to iii) were retained and implemented in the open source CFD softwareOpenFOAM. The simulation results were first validated against the analytic solutionof an infinite electric rod. Perfect agreement was obtained for all the models tested.The electromagnetic models i) to iii) were then coupled with thermal fluid mechanicsin OpenFOAM, and applied to the calculation of an axi-symmetric Gas Tungsten ArcWelding (GTAW) test case with short arc (2mm) and truncated conical electrode tip.Models i) and ii) lead to the same simulation results, but not model iii). Model iii)is suited in the specific limit of long axi-symmetric arc, with negligible electrode tipeffect. For short axi-symmetric arc, the more general axi-symmetric formulation ofmodel ii) should instead be used.

  • 28.
    Chung, Sunjae
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Mohseni, Seyed Majid
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Fallahi, Vahid
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Nguyen, T. N. Anh
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Benatmane, Nadjib
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Dumas, R. K.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Tunable spin configuration in [Co/Ni]-NiFe spring magnets2013In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 46, no 12, p. 125004-Article in journal (Refereed)
    Abstract [en]

    We investigate a tunable spin configuration in [Co/Ni](4)/Co-NiFe exchange spring magnets. The strong perpendicular magnetic anisotropy of the Co/Ni multilayer, which competes with the in-plane shape anisotropy of the Ni81Fe19 (Py) layer, allows for unique magnetic configurations. By varying the NiFe thickness (t(NiFe)) from 2.6 to 3.0 nm, we show that the magnetization tilt angle can be easily tuned from completely out-of-plane (0 degrees) to in-plane (90 degrees). This transition, which occurs for a small range of t(NiFe), can be estimated from the major loop remanence and one-dimensional micromagnetic calculations. These tunable magnetization tilt spring magnets are highly promising for future applications in spin-transfer torque-based devices.

  • 29. 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.

  • 30.
    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.

  • 31.
    Dalarsson, Mariana
    et al.
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Nordebo, Sven
    Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
    Sjöberg, Daniel
    Lund University.
    Bayford, Richard
    Middlesex Univ, UK.
    Absorption and optimal plasmonic resonances for small ellipsoidal particles in lossy media2017In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 50, no 34, article id 345401Article in journal (Refereed)
    Abstract [en]

    A new simplified formula is derived for the absorption cross section of small dielectric ellipsoidal particles embedded in lossy media. The new expression leads directly to a closed form solution for the optimal conjugate match with respect to the surrounding medium, i.e. the optimal permittivity of the ellipsoidal particle that maximizes the absorption at any given frequency. This defines the optimal plasmonic resonance for the ellipsoid. The optimal conjugate match represents a metamaterial in the sense that the corresponding optimal permittivity function may have negative real part (inductive properties), and can not in general be implemented as a passive material over a given bandwidth. A necessary and sufficient condition is derived for the feasibility of tuning the Drude model to the optimal conjugate match at a single frequency, and it is found that all the prolate spheroids and some of the (not too flat) oblate spheroids can be tuned into optimal plasmonic resonance at any desired center frequency. Numerical examples are given to illustrate the analysis. Except for the general understanding of plasmonic resonances in lossy media, it is also anticipated that the new results can be useful for feasibility studies with e.g. the radiotherapeutic hyperthermia based methods to treat cancer based on electrophoretic heating in gold nanoparticle suspensions using microwave radiation.

  • 32. 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.

  • 33.
    Delsing, Per
    et al.
    Chalmers Univ Technol, Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
    Wiklund, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Westerhausen, Christoph
    Univ Augsburg, Inst Phys, D-86159 Augsburg, Germany.;NIM, Munich, Germany.;Ludwig Maximilians Univ Munchen, Ctr NanoSci CeNS, D-80799 Munich, Germany.;Univ Augsburg, Ctr Interdisciplinary Hlth Res ZIG, D-86135 Augsburg, Germany.;ACIT, D-86159 Augsburg, Germany..
    The 2019 surface acoustic waves roadmap2019In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 52, no 35, article id 353001Article, review/survey (Refereed)
    Abstract [en]

    Today, surface acoustic waves (SAWs) and bulk acoustic waves are already two of the very few phononic technologies of industrial relevance and can been found in a myriad of devices employing these nanoscale earthquakes on a chip. Acoustic radio frequency filters, for instance, are integral parts of wireless devices. SAWs in particular find applications in life sciences and microfluidics for sensing and mixing of tiny amounts of liquids. In addition to this continuously growing number of applications, SAWs are ideally suited to probe and control elementary excitations in condensed matter at the limit of single quantum excitations. Even collective excitations, classical or quantum are nowadays coherently interfaced by SAWs. This wide, highly diverse, interdisciplinary and continuously expanding spectrum literally unites advanced sensing and manipulation applications. Remarkably, SAW technology is inherently multiscale and spans from single atomic or nanoscopic units up even to the millimeter scale. The aim of this Roadmap is to present a snapshot of the present state of surface acoustic wave science and technology in 2019 and provide an opinion on the challenges and opportunities that the future holds from a group of renown experts, covering the interdisciplinary key areas, ranging from fundamental quantum effects to practical applications of acoustic devices in life science.

  • 34.
    dos Santos, R. B.
    et al.
    University of Federal Bahia, Brazil.
    Rivelino, R.
    University of Federal Bahia, Brazil.
    de Brito Mota, F.
    University of Federal Bahia, Brazil.
    Kostov Gueorguiev, Gueorgui
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Kakanakova-Gueorguie, Anelia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Dopant species with Al-Si and N-Si bonding in the MOCVD of AlN implementing trimethylaluminum, ammonia and silane2015In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 48, no 29, article id 295104Article in journal (Refereed)
    Abstract [en]

    We have investigated gas-phase reactions driven by silane (SiH4), which is the dopant precursor in the metalorganic chemical vapor deposition (MOCVD) of aluminum nitride (AlN) doped by silicon, with prime focus on determination of the associated energy barriers. Our theoretical strategy is based on combining density-functional methods with minimum energy path calculations. The outcome of these calculations is suggestive for kinetically plausible and chemically stable reaction species with Al-Si bonding such as (CH3)(2)AlSiH3 and N-Si bonding such as H2NSiH3. Within this theoretical perspective, we propose a view of these reaction species as relevant for the actual MOCVD of Si-doped AlN, which is otherwise known to be contributed by the reaction species (CH3)(2)AlNH2 with Al-N bonding. By reflecting on experimental evidence in the MOCVD of various doped semiconductor materials, it is anticipated that the availability of dopant species with Al-Si, and alternatively N-Si bonding near the hot deposition surface, can govern the incorporation of Si atoms, as well as other point defects, at the AlN surface.

  • 35. Dunsby, C.
    et al.
    Lanigan, P. M. P.
    McGinty, J.
    Elson, D. S.
    Requejo-Isidro, J.
    Munro, I.
    Galletly, N.
    McCann, F.
    Treanor, B.
    Önfelt, Björn
    Davis, D. M.
    Neil, M. A. A.
    French, P. M. W.
    An electronically tunable ultrafast laser source applied to fluorescence imaging and fluorescence lifetime imaging microscopy2004In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 37, no 23, p. 3296-3303Article in journal (Refereed)
    Abstract [en]

    Fluorescence imaging is used widely in microscopy and macroscopic imaging applications for fields ranging from biomedicine to materials science. A critical component for any fluorescence imaging system is the excitation source. Traditionally, wide-field systems use filtered thermal or arc-generated white light sources, while point scanning confocal microscope systems require spatially coherent (point-like) laser sources. Unfortunately, the limited range of visible wavelengths available from conventional laser sources constrains the design and usefulness of fluorescent probes in confocal microscopy. A 'hands-off' laser-like source, electronically tunable across the visible spectrum, would be invaluable for fluorescence imaging and provide new opportunities, e.g. automated excitation fingerprinting and in situ measurement of excitation cross-sections. Yet more information can be obtained using fluorescence lifetime imaging (FLIM), which requires that the light source be pulsed or rapidly modulated. We show how a white light continuum, generated by injecting femtosecond optical radiation into a micro-structured optical fibre, coupled with a simple prism-based tunable filter arrangement, can fulfil all these roles as a continuously electronically tunable (435-1150 nm) visible ultrafast light source in confocal, wide-field and FLIM systems.

  • 36.
    Dyakov, Sergey A.
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Dai, Jin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Near field thermal memory based on radiative phase bistability of VO22015In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 48, no 30, article id 305104Article in journal (Refereed)
    Abstract [en]

    We report the concept of a near-field memory device based on the radiative bistability effect in the system of two closely separated parallel plates of SiO2 and VO2 which exchange heat by thermal radiation in vacuum. We demonstrate that the VO2 plate, having metal-insulator transition at 340 K, has two thermodynamical steady-states. One can switch between the states using an external laser impulse. We show that due to near-field photon tunneling between the plates, the switching time is found to be only 5 ms which is several orders lower than in case of far field.

  • 37. 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.

  • 38.
    Eklund, Per
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Layered ternary M(n+1)AX(n) phases and their 2D derivative MXene: an overview from a thin-film perspective2017In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 50, no 11, article id 113001Article, review/survey (Refereed)
    Abstract [en]

    Inherently and artificially layered materials are commonly investigated both for fundamental scientific purposes and for technological application. When a layered material is thinned or delaminated to its physical limits, a two-dimensional (2D) material is formed and exhibits novel properties compared to its bulk parent phase. The complex layered phases known as MAX phases (where M = early transition metal, A = A-group element, e.g. Al or Si, and X = C or N) are an exciting model system for materials design and the understanding of process-structure-property relationships. When the A layers are selectively etched from the MAX phases, a new type of 2D material is formed, named MXene to emphasize the relation to the MAX phases and the parallel with graphene. Since their discovery in 2011, MXenes have rapidly become established as a novel class of 2D materials with remarkable possibilities for composition variations and property tuning. This article gives a brief overview of MAX phases and MXene from a thin-film perspective, reviewing theory, characterization by electron microscopy, properties and how these are affected by the change in dimensionality, and outstanding challenges.

  • 39.
    Engström, Christian
    Lund University, Department of Electrical and Information Technology.
    Bounds on the effective tensor and structural parameters for anisotropic two-phase composite material2005In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 38, p. 3695-3702Article in journal (Refereed)
  • 40.
    Engström, Christian
    Lund University, Sweden.
    Bounds on the effective tensor and structural parameters for anisotropic two-phase composite material2005In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 38, p. 3695-3702Article in journal (Refereed)
    Abstract [en]

    This paper is concerned with the estimation of macroscopic properties such as the permittivity or the thermal conductivity of a composite material from the microstructure. A new method of estimating the microstructural parameters, such as the volume fraction of anisotropic two-phase composite material, is derived. The parameters are estimated using information from measurements of the random material or, in the periodic case, from numerical experiments. The method is used to derive new bounds on the effective tensor that incorporates information from measurements of a related parameter. These new bounds are called cross-property bounds. New tight bounds on low-order microstructural parameters are given in the anisotropic case.

  • 41.
    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.

  • 42.
    Fernando, Harendra
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Canning, J.
    Wosinski, Lech
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Jaskorzynska, Bozena
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Engineering UV-photosensitivity in planar lightwave circuits by plasma enhanced chemical vapour deposition2004In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 37, no 20, p. 2804-2809Article in journal (Refereed)
    Abstract [en]

    Ion bombarding conditions were used to modify glass properties in silica-on-silicon systems during plasma enhanced chemical vapour deposition (PECVD). The induced structural modifications in the SiO2/Si system resulted in different photosensitive responses when irradiated by ArF pulsed laser operating at 193 nm wavelength. Fourier transform infrared spectroscopy was used to study the structural modifications triggered by ion bombarding conditions during film growth. The results were further confirmed by additional characterizations with regard to density (etch rate), refractive index and surface topographic measurements. The demonstrated method could be used not only to engineer UV-photosensitivity but also to control and compensate birefringence in planar lightwave devices.

  • 43.
    Festy, F.
    et al.
    The University of Birmingham.
    Svensson, Krister
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science. The University of Birmingham.
    Laitenberger, P.
    The University of Birmingham.
    Palmer, R.E.
    The University of Birmingham.
    Imaging surfaces with reflected electrons from a field-emission STM: image contrast mechanisms2001In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, no 34, p. 1849-Article in journal (Refereed)
    Abstract [en]

    Electrons backscattered from a scanning tunnelling microscope operating in the field emission mode have been collected to produce images of a rough Si(111) surface. We have obtained a spatial resolution of about 40 nm in such images. Comparison between backscattered electron images and topographic images reveals that edge enhancement and shadowing are important contrast mechanisms.

  • 44.
    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.

  • 45.
    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.

  • 46.
    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. 

  • 47. Gan, Zhixing
    et al.
    Wu, Xinghong
    Xu, Hao
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Zhang, Ning
    Nie, Shouping
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Electron transition pathways of photoluminescence from 3C-SiC nanocrystals unraveled by steady-state, blinking and time-resolved photoluminescence measurement2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 27Article in journal (Refereed)
    Abstract [en]

    The cubic phase SiC nanocrystals (3C-SiC NCs) have been extensively studied for electronics and photonics applications. In this work we study the electron transition pathways of photoluminescence (PL) from 3C-SiC NCs. It is found through measuring the steady-state, blinking and time-resolved PL spectra that surface passivation by glycerol improved the steady-state PL intensity (it does not modify the emission wavelength) and the NCs fluoresced more steadily. The PL decay lifetimes are shown to be the same when the detection wavelength is modified to scan the broad PL peak, implying that the broad PL peak is originated from the distribution of NCs' sizes. Furthermore, the PL decay lifetimes are not modified by the surface passivation. It is concluded that for PL, the electron is photoexcited from the ground state in the NC to a high-energy excited state, relaxes to the first excited state then radiatively recombines to the ground state to emit a photon. The photoexcited electron at the high-energy excited state could transit to the surface state, resulting in a reduced PL intensity and a decreased on-state dwell time in the blinking trajectory. The PL decay lifetime data implies that the two principal electron transition pathways of (a) high-energy excited state double right arrow the first excited state double right arrow the ground state, and (b) high-energy excited state double right arrow surface state double right arrow the ground state are independent from each other. We strongly believe that such a deep knowledge about 3C-SiC NCs will open new doors to harness them for novel applications.

  • 48.
    Gharavi, Mohammad Amin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Kerdsongpanya, Sit
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Rensselaer Polytech Inst, NY 12180 USA.
    Schmidt, Susann
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Eriksson, Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Nong, N. V
    Tech Univ Denmark, Denmark.
    Lu, Jun
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Balke, B.
    Johannes Gutenberg Univ Mainz, Germany.
    Fournier, D.
    UPMC Univ Paris 06, France.
    Belliard, L.
    UPMC Univ Paris 06, France.
    Le Febvrier, Arnaud
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Pallier, Camille
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Microstructure and thermoelectric properties of CrN and CrN/Cr2N thin films2018In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 35, article id 355302Article in journal (Refereed)
    Abstract [en]

    CrN thin films with an N/Cr ratio of 95% were deposited by reactive magnetron sputtering onto (0001) sapphire substrates. X-ray diffraction and pole figure texture analysis show CrN (111) epitaxial growth in a twin domain fashion. By changing the nitrogen versus argon gas flow mixture and the deposition temperature, thin films with different surface morphologies ranging from grainy rough textures to flat and smooth films were prepared. These parameters can also affect the CrN(x )system, with the film compound changing between semiconducting CrN and metallic Cr2N through the regulation of the nitrogen content of the gas flow and the deposition temperature at a constant deposition pressure. Thermoelectric measurements (electrical resistivity and Seebeck coefficient), scanning electron microscopy, and transmission electron microscopy imaging confirm the changing electrical resistivity between 0.75 and 300 m omega cm, the changing Seebeck coefficient values between 140 and 230 mu VK-1, and the differences in surface morphology and microstructure as higher temperatures result in lower electrical resistivity while gas flow mixtures with higher nitrogen content result in single phase cubic CrN.

  • 49. Gogova, D.
    et al.
    Hemmingsson, Carl
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Talik, E.
    Kruczek, M.
    Tuomisto, F.
    Saarinen, K.
    Investigation of the structural and optical properties of free-standing GaN grown by HVPE2005In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 38, no 14, p. 2332-2337Article in journal (Refereed)
    Abstract [en]

    The potential of the high-growth rate hydride vapour phase epitaxy technique and laser lift-off for the fabrication of free-standing GaN substrates is explored. Structural and optical properties of 300 νm thick free-standing GaN have been investigated employing different analytical techniques. The x-ray diffraction (XRD) measurements prove good crystalline quality of the material grown. A comparatively low value of (3 ± 1) × 1016 cm-3 of Ga vacancy-related defects is inferred from positron annihilation spectroscopy data. Complete strain relaxation is observed on the Ga-polar face of the free-standing GaN by XRD and Raman spectroscopy measurements. The strain-free homoepitaxy will significantly reduce the defect density, and thus an improvement of the device performance and lifetime can be realized. © 2005 IOP Publishing Ltd.

  • 50.
    Greczynski, Grzegorz
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Rhein Westfal TH Aachen, Germany.
    Mraz, S.
    Rhein Westfal TH Aachen, Germany.
    Schneider, J. M.
    Rhein Westfal TH Aachen, Germany.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Substantial difference in target surface chemistry between reactive dc and high power impulse magnetron sputtering2018In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 5, article id 05LT01Article in journal (Refereed)
    Abstract [en]

    The nitride layer formed in the target race track during the deposition of stoichiometric TiN thin films is a factor 2.5 thicker for high power impulse magnetron sputtering (HIPIMS), compared to conventional dc processing (DCMS). The phenomenon is explained using x-ray photoelectron spectroscopy analysis of the as-operated Ti target surface chemistry supported by sputter depth profiles, dynamic Monte Carlo simulations employing the TRIDYN code, and plasma chemical investigations by ion mass spectrometry. The target chemistry and the thickness of the nitride layer are found to be determined by the implantation of nitrogen ions, predominantly N+ and N-2(+) for HIPIMS and DCMS, respectively. Knowledge of this method-inherent difference enables robust processing of high quality functional coatings.

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