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  • 1.
    Bingham, Robert
    et al.
    Rutherford Appleton Lab, England .
    Eliasson, Bengt
    Ruhr University of Bochum, Germany .
    Tito Mendonca, Jose
    Institute Super Tecn, Portugal .
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Ion acceleration by Alfven waves on auroral field lines2013In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 87, no 5Article in journal (Refereed)
    Abstract [en]

    Observations of ion acceleration along auroral field lines at the boundary of the plasma sheet and tail lobe of the Earth show that the energy of the ions increases with decreasing density. The observations can be explained by ion acceleration through Landau resonance with kinetic Alfven waves (KAWs) such that k(A) . v(i) = omega(A), where k(A) is the wave vector, v(i) is the ion resonance velocity and omega(A) is the Alfven wave frequency. The ion resonance velocities are proportional to the Alfven velocity which increases with decreasing density. This is in agreement with the data if the process is occurring at the plasma sheet tail lobe boundary. A quasi-linear theory of ion acceleration by KAWs is presented. These ions propagate both down towards and away from the Earth. The paths of the Freja and Polar satellites indicate that the acceleration takes place between the two satellites, between 1Re and 5Re. The downward propagating ions develop a horseshoe-type of distribution which has a positive slope in the perpendicular direction. This type of distribution can produce intense lower hybrid wave activity, which is also observed. Finally, the filamentation of shear Alfven waves is considered. It may be responsible for large-scale density striations.

  • 2.
    Bostrom, M.
    et al.
    University of Oslo, Norway; Norwegian University of Science and Technology, Norway.
    Thiyam, P.
    Royal Institute Technology, Sweden.
    Persson, C.
    University of Oslo, Norway; Royal Institute Technology, Sweden; University of Oslo, Norway.
    Parsons, D. F.
    Australian National University, Australia.
    Buhmann, S. Y.
    University of Freiburg, Germany; University of Freiburg, Germany.
    Brevik, I.
    Norwegian University of Science and Technology, Norway.
    Sernelius, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Non-perturbative theory of dispersion interactions2015In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 90, no 3, p. 035405-Article in journal (Refereed)
    Abstract [en]

    Some open questions exist with fluctuation-induced forces between extended dipoles. Conventional intuition derives from large-separation perturbative approximations to dispersion force theory. Here, we present a full non-perturbative theory. In addition, we discuss how one can take into account finite dipole size corrections. It is of fundamental value to investigate the limits of validity of the perturbative dispersion force theory.

  • 3.
    Brodin, G.
    et al.
    Umeå University, Sweden.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    A new decay channel for upper-hybrid waves2016In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 91, no 10, article id 104005Article in journal (Refereed)
    Abstract [en]

    We look here at a three-wave interaction process involving only electrostatic waves in an electron plasma with stationary ions. Special attention is given to the case with an upper-hybrid wave as a pump wave, where a new decay channel is pointed out. The corresponding growth rate is calculated.

  • 4.
    Brodin, G
    et al.
    Umeå University.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Three-wave coupling coefficients for a magnetized plasma2012In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 85, no 3, p. 035504-Article in journal (Refereed)
    Abstract [en]

    The resonant interaction between three waves in a uniform magnetized plasma is reconsidered. Starting from previous kinetic expressions, which contain a general but too little used result, we are able to improve the formulae. This leads to an explicit expression for the three-wave coupling coefficient which applies for arbitrary wave propagation in a magnetized Vlasov plasma.

  • 5.
    Brodin, Gert
    et al.
    Umeå University, Sweden.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Juul Rasmussen, Jens
    Technical University of Denmark, Denmark.
    Focus issue to honour Hans L Pecseli on his 70th birthday2017In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 92, no 1, article id 010301Article in journal (Other academic)
    Abstract [en]

    n/a

  • 6.
    Buyanova, Irina
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Wagner, Matthias
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Lindström, J. L.
    Amano, H.
    Aksaki, I.
    Effect of electron irradiation on optical properties of gallium nitride1999In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T79, p. 72-75Article in journal (Refereed)
    Abstract [en]

     The effect of electron irradiation on the optical properties of GaN epilayers is studied in detail by photoluminescence (PL) spectroscopy. The most common types of GaN material are used, i.e. strained heteroepitaxial layers grown on 6H SiC or Al2O3 substrates, and thick bulk-like layers with the conductivity varying from n-type to semi-insulating and p-type. The main effects of electron irradiation on all investigated samples are found to be as follows: (i) a radiation-induced quenching of excitonic emissions in the near band gap region; (ii) an appearance of broad overlapping PL emissions within the spectral range 0.7-1.1 eV and (iii) the appearance of a PL band with a sharp no-phonon (NP) line at around 0.88 eV followed by a rich phonon assisted sideband. The 0.88 eV band is shown to originate from an internal transition of a deep defect. With increasing temperature a hot PL line can be observed at about 2-4 meV above the NP line, originating from higher lying excited states of the defect. The electronic structure of the 0.88 eV defect is shown to be very sensitive to the internal strain field in the GaN epilayers.

  • 7.
    Chen, Weimin
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Buyanov, A. V.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Lundström, Tim
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Bi, W. G.
    Zeng, Y. P.
    Tu, C. W.
    Transport properties of intrinsically and extrinsically modulation doped InP/InGaAs heterostructures1999In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T79, p. 103-105Article in journal (Refereed)
    Abstract [en]

     Transport properties in a new type of modulation doped InP/InGaAs systems, where the n-type doping is provided by intrinsic PIn-antisite defects rather than foreign impurities, are studied by Shubnikov-de-Haas (SdH) oscillations and low-field Hall effect measurements. A close comparison of transport properties is made between these intrinsically modulation doped structures with extrinsically doped structures, with the emphasis on two of the most important physical processes i.e. doping efficiency and scattering mechanism. It is found that the efficiency of the intrinsic modulation doping is at least as high as the extrinsic modulation doping. The mobilities of the two dimensional electron gas (2DEG) derived from Hall and SdH measurements are shown to be higher in the intrinsically doped structures as compared to the extrinsically doped structures. This is attributed to a reduced scattering of the 2DEG by the remote parent dopants, due to e.g. an increased screening of the scattering potential by the excess free electrons present in the intrinsic doping region due to auto-ionization of the PIn antisite.

  • 8.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    Chapman, S.C.
    Rowlands, G.
    Andersson, N.
    National Supercomputer Centre (NSC), University of Linköping, Valla Campus, SE-58183 Linköping, Sweden.
    Simulating thermal noise2004In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 69, no 6, p. 456-460Article in journal (Refereed)
    Abstract [en]

    Thermal noise measurements by space-borne antennas are commonly used to determine plasma parameters like the electron density and the plasma temperature from the noise spectra. It would be desirable to have a controlled experiment in which noise from a plasma with known properties is sampled in space and in time and which results can then be used to reproduce the satellite measurements. Here we examine the possibility to use particle-in-cell (PIC) simulations as such an experiment. In this work we present a statistically averaged noise spectrum computed with a PIC code for a simple single-Maxwellian and unmagnetized electron plasma and we compare it to both, the thermal noise spectrum for the corresponding real plasma and the noise spectrum we would anticipate from our numerical scheme. We find that we can produce noise fields with sufficiently low amplitudes to keep the plasma in a linear regime. We show that the simulation noise at low and at large wave numbers differs not only from thermal noise of a physical plasma but also from the numerical noise we would expect from our numerical scheme. We explain the drop of the noise power at low wave numbers by our initial conditions. We find experimentally the relation that connects the theoretical noise spectrum for our simulation code with that we actually measure, provided that the phase velocity of the noise is less than the maximum velocity of the computational particles.

  • 9.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    Bret, Antoine
    ETSI Ind Univ Castilla-La Mancha.
    Electric field generation by the electron beam filamentation instability: filament size effects2010In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 81, no 1, p. 015502-Article in journal (Refereed)
    Abstract [en]

    The filamentation instability (FI) of counter-propagating beams of electrons is modelled with a particle-in-cell simulation in one spatial dimension and with a high statistical plasma representation. The simulation direction is orthogonal to the beam velocity vector. Both electron beams have initially equal densities, temperatures and moduli of their non-relativistic mean velocities. The FI is electromagnetic in this case. A previous study of a small filament demonstrated that the magnetic pressure gradient force (MPGF) results in a nonlinearly driven electrostatic field. The probably small contribution of the thermal pressure gradient to the force balance implied that the electrostatic field performed undamped oscillations around a background electric field. Here, we consider larger filaments, which reach a stronger electrostatic potential when they saturate. The electron heating is enhanced and electrostatic electron phase space holes form. The competition of several smaller filaments, which grow simultaneously with the large filament, also perturbs the balance between the electrostatic and magnetic fields. The oscillations are damped but the final electric field amplitude is still determined by the MPGF.

  • 10.
    Gogova, Daniela
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Kasic, A.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Larsson, Henrik
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Pécz, B.
    Research Institute for Technical Physics and Materials Science of the Hungarian Academy of Sci., Budapest, Hungary .
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Monemar, Bo
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Characterization of high-quality free-standing GaN grown by HVPE2004In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T114, p. 18-21Article in journal (Refereed)
    Abstract [en]

    Single-crystalline 330µm thick GaN has been grown on 2'' Al2O3 (0 0 0 1) by hydride vapour phase epitaxy (HVPE). Upon laser-induced lift-off the GaN was delaminated from the sapphire substrate, and bulk-like free-standing GaN was achieved. Various characterization methods were utilized to assess the structural and optical quality of the freestanding material. The X-ray rocking curves of the (1 0–1 4) and (0 0 0 2) diffraction peaks revealed full width at half maximum (FWHM) values of 96 and 129arcsec, respectively. These data compare well with the smallest corresponding values published so far for bulk-like HVPE-GaN. The dislocation density determined by plan-view transmission electron microscopy studies is 1–2 × 107cm–2. The low-temperature near-band-gap photoluminescence spectrum shows the main donor bound exciton (DBE) peak at 3.4718eV with a FWHM of 1.4meV, verifying the high crystalline quality of the bulk-like GaN. The DBE peak position suggests complete stress relief. The phonon spectra measured by infrared spectroscopic ellipsometry confirm as well, that the free-standing material is of high crystalline quality and virtually stress-free.

  • 11.
    Gradov, O.M.
    et al.
    N.S. Kurnakov Institute of the Russian Academy of Sciences.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Shukla, P.K.
    Department of Physics Umea University.
    Non-linear effects in a cold electron plasma with non-uniform density profile2008In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 77, p. 055503-1-055503-3Article in journal (Refereed)
    Abstract [en]

     A new step forward on the theory for two-dimensional wave propagation is outlined for a non-uniform plasma with a smooth density profile. A way to excite envelope solitary waves with certain shapes is described. The corresponding wave space structure is calculated, and the restrictions on the wave profile along the direction of wave propagation are noticed.

  • 12.
    Henry, Anne
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Forsberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Linnarsson, M. K.
    Solid State Electronics, Royal Institute of Technology, SE-164 40 Kista, Sweden.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Determination of nitrogen doping concentration in doped 4H-SiC epilayers by low temperature photoluminescence2005In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 72, no 2-3, p. 254-257Article in journal (Refereed)
    Abstract [en]

    A complete calibration of nitrogen concentration in doped 4H-SiC material is presented. This is done in the very large range of doping available today, i.e. from low 1014 to 1019 cm-3. The samples are 4H-SiC films fabricated by hot-wall chemical vapour deposition. Low temperature photoluminescence is used as the experimental tool. For doping concentrations less than 8 × 1017 cm-3 comparison between the intensity of various luminescence lines is used, whereas for doping higher than 3 × 1018 cm-3 the energy position of an observed broad band allows the determination of the doping level.

  • 13.
    Ivanov, Ivan Gueorguiev
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Resonant ionization of shallow donors in electric field2014In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 89, no 8, p. 085802-Article in journal (Refereed)
    Abstract [en]

    In this paper, we report on our experimental observations of the resonant ionization of a phosphorus donor in silicon in a homogeneous electric field, which is expressed in the sudden rise of the conductivity of the sample at a low temperature when the electric field approaches the critical value of ∼3.2 MV m-1. The effect is discussed in terms of the field-induced interaction of the states using a simplified model based on the effective-mass theory. The results from our model are qualitatively similar to the previously published advanced model base, which is based on the first principles; this predicts the ionization thresholds at approximate fields of 2.45 and 3.25 MV m-1, the latter being in very good agreement with our experiment. The possibility of observing more than one resonance is also discussed.

  • 14.
    Janson, M. S.
    et al.
    Royal Inst Technol KTH, Dept Microelect & Informat Technol, S-16440 Kista, Sweden .
    Linnarsson, M. K.
    Royal Inst Technol KTH, Dept Microelect & Informat Technol, S-16440 Kista, Sweden .
    Hallen, A.
    Royal Inst Technol KTH, Dept Microelect & Informat Technol, S-16440 Kista, Sweden .
    Svensson, B. G.
    Royal Inst Technol KTH, Dept Microelect & Informat Technol, S-16440 Kista, Sweden .
    Achtziger, N.
    Univ Jena, Inst Festkorperphys, D-07743 Jena, Germany .
    Unéus, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Lloyd-Spets, Anita
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Forsberg, Urban
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Hydrogen in the wide bandgap semiconductor silicon carbide2004In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T108, p. 99-112Article in journal (Refereed)
    Abstract [en]

    In this paper we give a review of our recent results related to the incorporation of hydrogen (H) in silicon carbide (SiC) and its interaction with acceptor doping atoms and implantation induced defects. Hydrogen is an abundant impurity in the growth of epitaxial SiC since it is present in the precursor gases and since H-2 is used as the carrier gas. High concentrations of hydrogen are indeed incorporated into highly doped p-type epi-layers and it is shown that the main source is the carrier gas. Furthermore, it is revealed that the entire substrate becomes homogeneously filled with hydrogen during growth and that this hydrogen is more thermally stable than that in the epi-layer. Incorporation of hydrogen from an H-2 ambient, at temperatures considerably lower than those used for epitaxy, is also demonstrated in p-type samples coated with a catalytic metal film. This effect is most likely the cause for the increased series resistance observed in p-type SiC Schottky sensor devices using a catalytic metal gate after annealing at 600 degrees C in a H-2 containing ambient. Hydrogen is found to passivate the acceptors Al and B by forming electrically neutral H-acceptor complexes. Unlike in Si and GaAs, the two H-acceptor complexes in SiC exhibit very different dissociation energies, suggesting that the atomic configurations of the complexes are significantly different. The migration of mobile hydrogen in the presence of externally applied, or internal built-in, electric fields further reveals that hydrogen is present as H+ in p-type SiC. Finally, the redistribution and subsequent out-diffusion of low energy implanted H-1 and H-2 is investigated. Two annealing phases for the redistribution are observed, and the activation energies for the processes are extracted.

  • 15.
    Karimov, A. R.
    et al.
    Russian Academic Science, Russia; National Research Nucl University of MEPhI, Russia.
    Yu, M. Y.
    Zhejiang University, Peoples R China; Ruhr University of Bochum, Germany.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    A new class of exact solutions for Vlasov-Poisson plasmas2016In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 91, no 11, p. 114002-Article in journal (Refereed)
    Abstract [en]

    A new class of exact solutions of the Vlasov-Poisson equations based on the Jeans theorem is considered. The self-consistent solutions for the evolution of the system from given initial particle distributions make use of particular invariants of particle motion with predetermined spatial structure. The relation between the time-dependent coefficients of the latter and the macroscopic plasma quantities, or moments of the distribution function, are obtained. As an illustration, the evolution of an expanding plasma with oscillations of the electron and ion expansion fronts is presented.

  • 16.
    Klason, P.
    et al.
    Laboratory of Physical Electronics and Photonics, Department of Physics, Göteborg University, Göteborg, Sweden.
    Magnusson, Karin
    Laboratory of Physical Electronics and Photonics, Department of Physics, Göteborg University, Göteborg, Sweden.
    Nour, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Wahab, Qamar Ul
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Synthesis and structural and optical properties of ZnO micro- and nanostructures grown by the vapour-liquid-solid method2006In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T126, p. 53-56Article in journal (Refereed)
    Abstract [en]

    ZnO micro- and nanostructures have been grown by the catalytic vapour - liquid - solid method on silicon and silicon carbide. These micro- and nanostructures were characterized by scanning electron microscope, x-ray diffraction and photoluminescence measurements. The characterization shows that the ZnO nano- and microrods grown have diameters of around 200 nm on the Si substrates and 600 nm when using the SiC substrates. The length ranges from 0.5 to 10 mu m.

  • 17.
    Lu, Weifang
    et al.
    Technical University of Denmark, Denmark.
    Ou, Yiyu
    Technical University of Denmark, Denmark.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Fadil, Ahmed
    Technical University of Denmark, Denmark.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Michael Petersen, Paul
    Technical University of Denmark, Denmark.
    Ou, Haiyan
    Technical University of Denmark, Denmark.
    Surface passivation of nano-textured fluorescent SiC by atomic layer deposited TiO22016In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 91, no 7, p. 074001-Article in journal (Refereed)
    Abstract [en]

    Nano-textured surfaces have played a key role in optoelectronic materials to enhance the light extraction efficiency. In this work, morphology and optical properties of nano-textured SiC covered with atomic layer deposited (ALD) TiO2 were investigated. In order to obtain a high quality surface for TiO2 deposition, a three-step cleaning procedure was introduced after RIE etching. The morphology of anatase TiO2 indicates that the nano-textured substrate has a much higher surface nucleated grain density than a flat substrate at the beginning of the deposition process. The corresponding reflectance increases with TiO2 thickness due to increased surface diffuse reflection. The passivation effect of ALD TiO2 thin film on the nano-textured fluorescent 6H-SiC sample was also investigated and a PL intensity improvement of 8.05% was obtained due to the surface passivation.

  • 18.
    Mendonca, J. T.
    et al.
    Instituto Superior Técnico, Lisboa.
    Onishchenko, O G
    Institute of Physics of the Earth, Moscow, Russia.
    Pokhotelov, O A
    Institute of Physics of the Earth, Moscow, Russia.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Wave-kinetic description of atmospheric turbulence2014In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 89, p. 125004-Article in journal (Refereed)
    Abstract [en]

    We propose a wave-kinetic description of atmospheric turbulence, where the turbulence spectrum is described as a gas of quasi-particles. We apply this description to the case of zonal structures in the atmosphere, which can be excited by internal gravity wave turbulence. A general expression for the instability growth rates is derived, and the particular example of a nearly mono-kinetic turbulent spectrum is discussed.

  • 19.
    Mendonca, J. T.
    et al.
    Institute Super Tecn, Portugal.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Acoustic-gravity waves in the atmosphere: from Zakharov equations to wave-kinetics2015In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 90, no 5, p. 055001-Article in journal (Refereed)
    Abstract [en]

    We develop a wave-kinetic description of acoustic-gravity (AG) waves in the atmosphere. In our paper the high frequency spectrum of waves is described as a gas of quasi-particles. Starting from the Zakharov-type of equations, where coupling between fast and slow density perturbations is considered, we derive the corresponding wave-kinetic equations, written in terms of an appropriate Wigner function. This provides an alternative description for the nonlinear interaction between the two dispersion branches of the AG waves.

  • 20.
    Nguyen, Son Tien
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Lindström, J. L.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Janzén, Erik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    A complex defect related to the carbon vacancy in 4H and 6H SiC1999In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T79, p. 46-49Article in journal (Refereed)
    Abstract [en]

     Electron paramagnetic resonance (EPR) was used to study defects in 4H and 6H SiC irradiated with 2.5 MeV electrons at room temperature. When the dose of irradiation reaches ~ 5 × 1017 electrons/cm2, an EPR spectrum appears. In both 4H and 6H SiC, the defect associated with this spectrum has C1h symmetry with an effective electron spin S = 1 and an isotropic g-value of 2.0063 ± 0.0002. The crystal-field parameter was determined as D = 1.65 and D = 1.67 GHz for 4H and 6H SiC, respectively. The principal crystal-field axis lies in the (11bar 20) plane and makes an angle of ~ 46° with the c-axis for both polytypes. A clear hyperfine structure from 29Si due to the interaction with four nearest silicon neighbours was observed, confirming that the defect is related to the carbon vacancy. The similarity in all respects including the annealing behaviour of the spectrum in both polytypes suggests that it belongs to the same defect. Based on the formation and its electronic structure, the defect is suggested to be a complex with one of the components being the carbon vacancy.

  • 21.
    Onishchenko, O. G.
    et al.
    Institute Phys Earth, Russia; Moscow Space Research Institute, Russia.
    Horton, W.
    Institute Mediterranean AMU, France; University of Texas Austin, TX 78712 USA; Aix Marseilles University, France.
    Pokhotelov, O. A.
    Institute Phys Earth, Russia.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Dust devil generation2014In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 89, no 7, p. 075606-Article in journal (Refereed)
    Abstract [en]

    The equations describing axi-symmetric nonlinear internal gravity waves in an unstable atmosphere are derived. A hydrodynamic model of a dust devil generation mechanism in such an atmosphere is investigated. It is shown that in an unstably stratified atmosphere the convective plumes with poloidal motion can grow exponentially. Furthermore, it is demonstrated that these convective plumes in an atmosphere with weak large scale toroidal motion are unstable with respect to three-dimensional dust devil generation.

  • 22.
    Ou, Yiyu
    et al.
    Technical University of Denmark, Lyngby.
    Jokubavicius, Valdas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Linnarsson, Margareta
    Royal Institute of Technology, Kista, Sweden .
    Yakimova, Rositza
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ou, Haiyan
    Technical University of Denmark, Lyngby.
    Characterization of donor–acceptor-pair emission in fluorescent 6H-SiC2012In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T148, p. 014003-Article in journal (Refereed)
    Abstract [en]

    We investigated donor–acceptor-pair emission in N–B-doped 6H-SiC samples by using photoluminescence (PL) and angle-resolved PL. It is shown that n-type doping with concentrations larger than 1018 cm−3 is favorable for observing luminescence, and increasing nitrogen results in stronger luminescence. A dopant concentration difference greater than 4×1018 cm−3 is proposed to help achieve intense PL. Angular-dependent PL was observed that was attributed to the Fabry–Pérot microcavity interference effect, and a strong luminescence intensity in a large emission angle range was also achieved. The results indicate that N–B-doped fluorescent SiC is a good wavelength converter in white LED applications.

  • 23. Petersson, L.-G.
    et al.
    Dannetun, Helen
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Karlsson, S.-E.
    Lundström, Ingemar
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Surface reactions on Pd studied with a hydrogen sensitive MOS-structure and photoelectron spectroscopy1982In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 25, no 6A, p. 818-825Article in journal (Refereed)
    Abstract [en]

    During the last couple of years catalytic reactions on Pd surfaces have been studied at our department by means of a hydrogen sensitive Pd-MOS structure and work function measurements. These studies have been performed at atmospheric pressures with Ar and O2 as carrier gases. We have now extended this type of measurements to the ultra-high vacuum (UHV) region and also combined them with both UV and, in certain cases, X-ray photoelectron spectroscopy (UPS, XPS) studies. With this technique we are able to detect about 0.001 of a monolayer of hydrogen, and changes in rate or equilibrium constants corresponding to changes in an energy coordinate of less than 10 meV. Furthermore, results from a Cd contaminated Pd-MOS structure indicates that the ability of Pd to dissociate H2 is related to a microscopic parameter and not to any general metal-like parameter.

  • 24.
    Pokhotelov, O.A.
    et al.
    Institute Phys Earth, Russia .
    Onishchenko, O.G.
    Institute Phys Earth, Russia .
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Physical mechanisms for electron mirror and field swelling modes2013In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 87, no 6, p. 065303-Article in journal (Refereed)
    Abstract [en]

    Ion mirror instability is dominant in planetary and cometary magnetosheaths and other high-beta plasmas where the ions are hotter than the electrons. It is associated with a zero-frequency non-propagating mode with the wave vector nearly perpendicular to the ambient magnetic field. The counterparts of this instability in hot electron plasmas are the field swelling and electron mirror instabilities. A theory for these instabilities was developed more than two decades ago (Basu B and Coppi B 1982 Phys. Rev. Lett. 48 799, 1984 Phys. Fluids 27 1187) within the framework of a fluid model. The connection between the two types of instabilities has been analyzed in (Migliuolo S 1986 J. Geophys. Res. 91 7981). In contrast to these papers, we shall here adopt the standard quasi-hydrodynamic approach that is usually used for the study of mirror instabilities. To analyze the electron mirror and field swelling instabilities, we will only use the perpendicular balance condition and the Liouville theorem. We have found that such a description is easier to understand and gives us increased physical insight into the basic physical features of both these instabilities.

  • 25.
    Robinson, Nathaniel D
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Edman, Ludvig
    Umeå University.
    Chhowalla, Manish
    Rutgers State University.
    Graphene electrodes for organic metal-free light-emitting devices2012In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T146, no 014023Article in journal (Refereed)
    Abstract [en]

    In addition to its fascinating electrical and mechanical properties, graphene is also an electrochemically stable and transparent electrode material. We demonstrate its applicability as both anode and cathode in a light-emitting electrochemical cell (LEC), an electrochemical analogue to a polymer organic light-emitting diode. Specifically, we summarize recent progress in carbon-based metal-free light-emitting devices enabled by chemically derived graphene cathodes on quartz and plastic substrates, and explain the advantages of using LECs in manufacturing large-area devices.

  • 26.
    Shukla, P K
    et al.
    Ruhr University of Bochum, Germany Ruhr University of Bochum, Germany University of Calif San Diego, CA 92093 USA University of Calif San Diego, CA 92093 USA .
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Acoustic gravity tornadoes in the atmosphere2012In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 86, no 6Article in journal (Refereed)
    Abstract [en]

    It is shown that three-dimensional (3D) acoustic gravity waves (AGWs) in the atmosphere can appear in the form of acoustic gravity tornadoes (AGTs) characterized by twisted density structures or density ropes carrying orbital angular momentum. For our purposes, we use a previously obtained 3D wave equation for AGWs, and show that this equation in the paraxial approximation admits solutions in the form of Laguerre-Gauss acoustic gravity vortex beams or AGTs/AG whirls with twisted density structures supporting the dynamics of the AGTs.

  • 27.
    Wagner, Matthias
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Lindström, J. L.
    Amano, H.
    Akasaki, I.
    Magnetooptical investigations on electron irradiated GaN1999In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T79, p. 53-55Article in journal (Refereed)
    Abstract [en]

    Optically Detected Magnetic Resonance (ODMR) and Level Anti-Crossing (LAC) experiments are employed to characterize the properties of two photoluminescence bands at 0.93 eV and 0.875 eV observable in electron irradiated GaN. Only one almost isotropic ODMR line and no LAC feature appear when monitoring the 0.93 eV emission, whereas two ODMR and two LAC signals can be found connected to the 0.875 eV band from spectral dependence studies. One possible explanation for the recombination leading to the 0.875 eV emission is a transition between excited states and ground state of a deep donor, where the ODMR signals arise from microwave induced transitions within the manifold of excited states. Within this manifold avoided crossings of the magnetic sublevels give rise to the observed LAC signals.

  • 28.
    Willander, Magnus
    et al.
    Chalmers.
    Nour, Omer
    Chalmers.
    Jain, S.C.
    IMEC, Leuven, Belgium.
    Silicon germanium strained layers and heterostructures2004In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T114, p. 22-30Article in journal (Refereed)
    Abstract [en]

    The integration of strained-Si1-xGex into Si technology has enhanced the performance and extended the functionality of Si based circuits. The improvement of device performance is observed in both AC as well as DC characteristics of these devices. The category of such devices includes field effect as well as bipolar families. Speed performance in some based circuits has reached limits previously dominated by III-V heterostructures based devices. In addition, for some optoelectronics applications including photodetectors it is now possible to easily integrate strained-Si1-xGex based optical devices into standard Silicon technology. The impact of integrating strained and relaxed Si1-xGex alloys into Si technology is important. It has lead to stimulate Si research as well as offers easy options for performances that requires very complicated and costly process if pure Si has to be used. In this paper we start by discussing the strain and stability of Si1-xGex alloys. The origin and the process responsible for transient enhanced diffusion (TED) in highly doped Si containing layers will be mentioned. Due to the importance of TED for thin highly doped Boron strained-Si1-xGex layers and its degrading consequences, possible suppression design methods will be presented. Quantum well p-channel MOSFETs (QW-PMOSFETs) based on thin buried QW are solution to the low speed and weak current derivability. Different aspects of designing these devices for a better performance are briefly reviewed. Other FETs based on tensile strained Si on relaxed Si1-xGex for n-channel and modulation doped field effect transistors (MODFETs) showed excellent performance. Record AC performance well above 200GHz for f(max) is already observed and this record is expected to increase in the coming years. Heterojunction bipolar transistors (HPTs) with thin strained-Si1-xGex highly doped base have lead to optimize the performance of the bipolar technology for many applications easily. The strategies of design and the most important designs of HBTs for optimum AC as well as DC are discussed in details. This technology is now mature enough and that is manifested in the appearance in the market nowadays. Si1-xGex based FETs circuits compatible with standard Si CMOS processes are soon expected to appear in the market. Finally, we briefly discuss the recent advances in Si1-xGex based infrared photodetectors.

  • 29.
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Developments in the growth of wide bandgap semiconductors2006In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T126, p. 121-126Article in journal (Refereed)
    Abstract [en]

    In this review we consider SiC, GaN, AlN and ZnO as belonging to the same class of compound wide bandgap semiconductors with hexagonal (wurtzite) structure. As such these materials exhibit some similar physical and electronic properties, but the level of material quality is distinctly different. This issue has been discussed with an emphasis on SiC as being a material with most complicated structure and respectively some specific defects.

  • 30.
    Yazdi, Gholamreza
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Materials Science . Linköping University, The Institute of Technology.
    Growth and morphology of AlN crystals2006In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T126, p. 127-130Article in journal (Refereed)
    Abstract [en]

    This study focused on growth dependencies, morphological forms and initial nucleation of aluminium nitride (AlN) crystals. Epitaxial layers of AlN have been grown on 4H-SiC substrates by sublimation recondensation in a radio frequency (RF) heated graphite furnace. Both AlN nuclei size and growth rate increased as temperature was increased and decreased as the pressure was increased. The results of these effects are different kinds of surface morphology. We have observed three modes of AlN single crystals: plate-like, columnar and needle-like. Optical microscopy and scanning electron microscopy (SEM) along with atomic force microscopy (AFM) were used to characterize the crystal surface morphology. Cathodoluminescence (CL) and x-ray diffraction (XRD) were applied to determine crystal quality and crystallographic orientation of the grown crystals.

  • 31.
    Zhang, Wenmin
    et al.
    Zhejiang University, Peoples R China .
    Yu, M Y
    Zhejiang University, Peoples R China .
    Karimov, A R
    Russian Academic Science, Russia .
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Intense oscillations in the expansion of an inhomogeneous cylindrical electron-positron layer2013In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 88, no 5, p. 055501-Article in journal (Refereed)
    Abstract [en]

    Large amplitude oscillations in the expansion of a cylindrical electron-positron plasma layer are investigated. The cold fluid equations and the Poissons equation are solved non-perturbatively in order to allow for very large amplitude oscillations. It is found that oscillations are self-excited during the expansion and can grow to very large amplitudes as the expansion slows down with time and the plasma density decreases. The kinetic energy of the expansion is thereby converted into that of the oscillations.

  • 32.
    Zhao, Qingxiang
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Klason, P.
    Willander, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Bergman, Peder
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    Jiang, W. L.
    Yang, J. H.
    Synthesis and characterization of ZnO nanostructures grown on Si substrates2006In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T126, p. 131-134Article in journal (Refereed)
    Abstract [en]

    ZnO nanostructures were grown by thermal evaporation technique on ( 001) Si substrate and were characterized by photoluminescence measurements, scanning electron microscope and x-ray measurements. The results show that the formation of ZnO nanostructures is strongly influenced by the growth conditions. By optimizing the growth conditions, orientated ZnO nanorods with a diameter of around 300 nm and lengths of 20 - 35 mu m have been achieved, and they show excellent optical properties. The laser action is observed at room temperature by using optical pumping.

1 - 32 of 32
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