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1.
  • Jones, R., et al. (författare)
  • Intrinsic defects and the D1 to D4 optical bands detected in plastically deformed Si
  • 2000
  • Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 222:1, s. 133-140
  • Tidskriftsartikel (refereegranskat)abstract
    • The properties of multi-vacancy and multi-interstitial defects that possess luminescent bands around 1 eV are reviewed. Prominent among these are the hexavacancy and tri- and tetra-self-interstitial defects. It is suggested that the formation of these defects on dislocation cores could lead to the D1 to D4 photoluminescent bands linked to dislocations in Si and SiGe.
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2.
  • Kordina, Olle, et al. (författare)
  • Growth of SiC by "Hot-Wall" CVD and HTCVD
  • 1997
  • Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 202:1, s. 321-334
  • Tidskriftsartikel (refereegranskat)abstract
    • A reactor concept for the growth of high-quality epitaxial SiC films has been investigated. The reactor concept is based on a hot-wall type susceptor which, due to the unique design, is very power efficient. Four different susceptors are discussed in terms of quality and uniformity of the grown material. The films are grown using the silane–propane–hydrogen system on off-axis (0001) 6H- and 4H-SiC substrates. Layers with doping levels in the low 1014 cm—3 showing strong free exciton emission in the photoluminescence spectra may readily be grown reproducibly in this system. The quality of the grown layers is also confirmed by the room temperature minority carrier lifetimes in the microsecond range and the optically detected cyclotron resonance data which give mobilities in excess of 100000 cm2/Vs at 6 K. Finally, a brief description will be given of the HTCVD technique which shows promising results in terms of high quality material grown at high growth rates.
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3.
  • Monemar, Bo, 1942-, et al. (författare)
  • The 3.466 eV Bound Exciton in GaN
  • 2001
  • Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 228:2, s. 489-492
  • Tidskriftsartikel (refereegranskat)abstract
    •  We discuss the available optical data for the 3.466 eV bound exciton in GaN, which has been a controversial issue in the recent literature. We conclude that the experimental results are only consistent with the identification as an exciton bound at a neutral acceptor with a spin-like bound hole. The chemical identity is still not clear.
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4.
  • Paskov, Plamen, 1959-, et al. (författare)
  • Anisotropy of the in-plane strain in GaN grown on A-plane sapphire
  • 2002
  • Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 234:3, s. 892-896
  • Tidskriftsartikel (refereegranskat)abstract
    • A comparative study of GaN layer grown by hydride vapour phase epitaxy on A-plane sapphire before and after removal of the substrate is presented. A large anisotropy of the in-plane strain in the as-grown sample is revealed by X-ray diffraction measurements and polarized photoluminescence. The strain anisotropy is found to modify the selection rules for the transitions leading to a splitting of the optically active states of the A and B excitons. Almost complete strain relaxation and recovery of the optical isotropy in the (0001) plane is observed in the free-standing layer.
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5.
  • Paskov, Plamen, 1959-, et al. (författare)
  • Internal structure of free excitons in GaN
  • 2001
  • Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 228:2, s. 467-470
  • Tidskriftsartikel (refereegranskat)abstract
    • Polarized photoluminescence is used to study the fine structure of free excitons in thick GaN layers grown on differently oriented sapphire substrates. The singlet-triplet splitting of the A exciton is measured and the exchange interaction constant in GaN is determined. For the samples grown on the a-plane sapphire, splitting of the A and B excitons induced by the uniaxial in-plane stress is also observed.
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6.
  • Paskov, Plamen, 1959-, et al. (författare)
  • Phonon-assisted photoluminescence in InGaN/GaN multiple quantum wells
  • 2002
  • Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 234:3, s. 755-758
  • Tidskriftsartikel (refereegranskat)abstract
    • The LO-phonon sidebands of the photoluminescence in InGaN/GaN multiple quantum wells has been investigated in the temperature range from 20 to 300 K. Analysing the intensity distribution among the phonon replicas, the strength of the exciton-phonon interaction has been estimated. The Huang-Rhys factor was found to be ÿ0.3, much larger than in GaN. The enhancement has been attributed to the exciton localization on a length scale smaller than the exciton Bohr radius and to the large internal electric field, which increases the spatial separation of the electron and hole charge densities along the growth axis.
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7.
  • Aberg, D, et al. (författare)
  • Ultra-shallow thermal donor formation in oxygen-containing ambient
  • 1998
  • Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 210, s. 527-532
  • Tidskriftsartikel (refereegranskat)abstract
    • Czochralski-grown phosphorus-doped (approximate to 2 x 10(14) cm(-3)) silicon wafers have been annealed in nitrogen, wet nitrogen, argon, oxygen, and vacuum ambients at 470 degrees C for times up to 500 h. Sample characterization was made with capacitance-voltage, four-point probe, DLTS, thermally stimulated capacitance, admittance spectroscopy, secondary ion-mass spectrometry, and Fourier transform infrared spectroscopy. This study finds a strong relation between the previously reported ultra-shallow thermal donors (USTDs) and shallow thermal donors (STDs), and it is shown that the net concentration of thermally formed donors is independent on annealing ambient within the experimental accuracy. It was found that the majority of formed donors for long anneals consisted of either STDs or USTDs, however, it was found that oxygen-containing ambient is indispensable for forming USTDs.
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8.
  • Achtziger, N, et al. (författare)
  • Mobility passivating effect and thermal stability of hydrogen in silicon carbide
  • 1998
  • Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 210, s. 395-399
  • Tidskriftsartikel (refereegranskat)abstract
    • The diffusion and passivating effect of hydrogen (isotope H-2) in epitaxial p-type SiC is studied by secondary ion mass spectrometry and capacitance-voltage profiling on Schottky diodes. The incorporation of hydrogen is achieved by low-energy ion implantation. The influence of implantation energy, temperature and subsequent annealing is presented. Annealing experiments with an electric field applied reveal a reactivation of passivated accepters and a H+ ion drift at a surprisingly low temperature of 530 K.
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9.
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10.
  • Arvanitidis, J., et al. (författare)
  • Comparative Raman Study of the 1D and 2D Polymeric Phases of C60 under Pressure
  • 1999
  • Ingår i: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. ; 215:1, s. 443-448
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of symmetry lowering on the phonon spectra as well as the pressure effects on the vibrational spectrum of polymerized C60 were studied by Raman spectroscopy. Drastic changes related to the splitting of degenerate modes of the C60 molecule were observed together with selected softening of some of them. In spite of many similarities in the Raman spectra of the one (1D) and two-dimensional (2D) polymeric forms of C60, some salient differences in the peak intensities and the appearance of complementary modes are evident. In the Raman spectrum of the 2D polymer under high pressure, new modes, which may be related to the deformations of molecular cages, appear. The observed pressure effects are reversible and the material remains stable for pressures up to 8.8 GPa.
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11.
  • Buyanova, Irina, 1960-, et al. (författare)
  • Mechanism for Light Emission in GaNAs/GaAs Structures Grown by Molecular Beam Epitaxy
  • 1999
  • Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 216:1, s. 125-129
  • Tidskriftsartikel (refereegranskat)abstract
    •  A detailed photoluminescence (PL) study reveals that the low-temperature PL emission in GaNAs epilayers and GaAs/GaNxAs1 - x quantum well structures grown by molecular beam epitaxy is governed by recombination of localized excitons. This conclusion is based on the analysis of the PL lineshape, its dependence on the excitation power and measurement temperature, as well as PL transient data. The depth of the localization potential is estimated as about 60 meV, varying slightly among the different structures.
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12.
  • Dixon, P., et al. (författare)
  • Nitrogen-Hydrogen Defects in GaP
  • 1998
  • Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 210:2, s. 321-326
  • Tidskriftsartikel (refereegranskat)abstract
    • Models of the nitrogen-hydrogen defect in GaP, which contain one and two H atoms, are investigated using ab initio density functional cluster theory. We find that a single H atom binding to N possesses two infrared absorption frequencies close to those attributed to an NH2 defect. The modes shift with its charge state consistent with the photo-sensitivity found for the defect. A third mode observed for this centre is assumed to be an overtone of the bend mode. The isotope shifts of the calculated modes are in excellent agreement with experiment in contrast with the model which contains two H atoms.
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13.
  • Kollar, J., et al. (författare)
  • Metal surfaces : Surface, step and kink formation energies
  • 2000
  • Ingår i: Physica status solidi. B, Basic research. - : WILEY-V C H VERLAG GMBH. - 0370-1972 .- 1521-3951. ; 217:1, s. 405-418
  • Tidskriftsartikel (refereegranskat)abstract
    • We review the surface, step, and kink energies in monoatomic metallic systems. A systematic comparison is given between the theoretical results based on density functional theory and available experimental data. Our calculated values are used to predict the equilibrium shapes of small metal particles, monoatomic surface islands, and the instability of different surface geometries.
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14.
  • Latham, Chris D., et al. (författare)
  • Di-carbon complexes in AlAs and GaAs
  • 1998
  • Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 210:2, s. 869-872
  • Tidskriftsartikel (refereegranskat)abstract
    • Heat treatment of heavily carbon doped AlAs and GaAs results in a loss of CAS shallow acceptors. In Raman scattering experiments on annealed CBE grown GaAs with 12C and 13C isotopes, and MOVPE grown AlAs it is found that the loss of carriers is accompanied by the appearance of two high frequency lines. These lie near to the stretch mode of an isolated C2 molecule (1855 cm-1). This is consistent with the formation of two types of di-carbon defects in these materials where the C atoms are bonded together and one or both of which act as a donor. Using a local density functional method to investigate the structure and dynamics of several di-carbon defects, we find that the dimer at an As site is bistable and aligned approximately in a [100] direction in the neutral charge state, and in a [110] direction when positively ionised. The calculated frequencies lie within 10% of the measured values in both materials. Other defects are investigated too with a view of determining the structures giving rise to the modes.
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15.
  • Adolph, David, 1971, et al. (författare)
  • Impact of O2 flow rate on the growth rate of ZnO(0001) and ZnO(000-1) on GaN by plasma-assisted molecular beam epitaxy
  • 2016
  • Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 253:8, s. 1523-1528
  • Tidskriftsartikel (refereegranskat)abstract
    • We studied the effects of a varying O$ flow rate on the growth of ZnO(0001) and ZnO(000-1) layers on GaN/Al2O3-templates by plasma-assisted molecular beam epitaxy. The O2 flow rate through the O-plasma source was varied between 0.25--4.5 standard cubic centimeters per minute corresponding to a growth chamber pressure between 3.0 x 10^-6 -- 5.0x10^-5 Torr. We found that the change of the O2 flow rate had a profound effect on the ZnO layer growth rate. A maximum growth rate was reached for an O2 flow rate of 1.0--2.0 standard cubic centimeters per minute. The same growth rate dependence on the O2 flow rate was observed for ZnO(0001) layers that were grown on GaN/4H-SiC buffer layers for verification. To assess the amount of active O contributing to the ZnO-growth, the spectral composition of the plasma was investigated with optical emission spectroscopy. The integrated optical emission line intensity reached a maximum for an O2 flow rate between 1.0--2.0 standard cubic centimeters per minute. Essentially all emission lines exhibited a maximum intensity for an O2 flow rate between 1.0--2.0 standard cubic centimeters per minute thus coinciding with the flow rate yielding the maximum growth rate.
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16.
  • Alcer, David, et al. (författare)
  • Comparison of Triethylgallium and Trimethylgallium Precursors for GaInP Nanowire Growth
  • 2021
  • Ingår i: Physica Status Solidi (B) Basic Research. - : Wiley. - 0370-1972. ; 258:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Nanowire (NW) arrays containing a top segment of GaxIn1–xP are investigated, comparing NWs grown using two different Ga precursors, trimethylgallium (TMGa) and triethylgallium (TEGa). TMGa is the precursor commonly used for the particle-assisted vapor–liquid–solid (VLS) growth of GaxIn1–xP NWs. However, it shows inefficient pyrolysis at typical NW growth conditions. The use of the alternative precursor TEGa is investigated by making a direct comparison between NWs grown using TEGa and TMGa at otherwise identical growth conditions. Growth rates, resulting NW materials composition, and time-resolved photoluminescence (TRPL) lifetimes are investigated. With increasing Ga content of the NWs, the TRPL lifetimes decrease, indicating trap states that are associated with GaP. Somewhat longer TRPL lifetimes for the samples grown using TEGa indicate a lower concentration of deep trap states. For doped NWs, it is found that the strong effect of the p-type dopant diethylzinc (DEZn) on the NW composition, observed for GaxIn1–xP NWs grown using TMGa, is absent when using TEGa.
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17.
  • Allali, Naoual, et al. (författare)
  • Covalent functionalization of few-wall carbon nanotubes by ferrocene derivatives for bioelectrochemical devices
  • 2012
  • Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 249:12, s. 2349-2352
  • Tidskriftsartikel (refereegranskat)abstract
    • The present work reports the covalent functionalization of few-wall CNTs (FWCNTs) by ferrocene derivatives to (i) improve their dispersion efficiency in water and (ii) graft electroactive chemical groups on their side-walls in order to promote electron transfer to biomolecules. The functionalized CNTs (f-CNTs) are used to modify a glassy carbon electrode and this modified electrode is used for oxidizing the cofactor NADH (dihydronicotinamide adenine dinucleotide).
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18.
  • Andres, Britta, et al. (författare)
  • Enhanced electrical and mechanical properties of nanographite electrodes for supercapacitors by addition of nanofibrillated cellulose
  • 2014
  • Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 251:12, s. 2581-2586
  • Tidskriftsartikel (refereegranskat)abstract
    • Graphene and porous carbon materials are widely used as electrodes in supercapacitors. In order to form mechanically stable electrodes, binders can be added to the conducting electrode material. However, most bindersdegrade the electrical performance of the electrodes. Here we show that by using nanofibrillated cellulose(NFC) as binder the electrical properties, such as capacitance, were enhanced. The highest capacitance was measured at a NFC content of approximately 10% in ratio to the total amount of active material. NFC is a good ionconductor and improves the access of ions in the electrodes. Thus, electrodes made of a mixture of nanographite and NFC achieved larger capacitances in supercapacitors than electrodes with nanographite only. In addition to electrical properties, NFC enhanced the mechanical stability and wet strength of the electrodes significantly. Furthermore, NFC stabilized the aqueous nanographite dispersions, which improved the processability. Galvanostatic cycling was performed and an initial transient behaviour of the supercapacitors during the first cycles was observed. However, stabilized supercapacitors showed efficiencies of 98–100 %.
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19.
  • Arnaudov, B, et al. (författare)
  • Hall effect data analysis of GaN n(+)n structures
  • 2002
  • Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 234:3, s. 872-876
  • Tidskriftsartikel (refereegranskat)abstract
    • We develop a model for analysis of Hall effect data of GaN structures composed of sublayers with different thicknesses and contacts placed on the top surface, We analysed the contributions of the conductivity of every sublayer of a planar sample taking into account the fact that the sample sublayers are partially connected in parallel to each other by series resistances formed in areas lying below the contacts from the upper layer. Correction factors, which reduce the contribution of the underlying layers to the measured whole sample conductivity, are obtained from the equations relevant to the respective equivalent circuit.
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20.
  • Bahrami, Danial, et al. (författare)
  • Impact of Electrical Current on Single GaAs Nanowire Structure
  • 2021
  • Ingår i: Physica Status Solidi (B) Basic Research. - : Wiley. - 0370-1972. ; 258:8
  • Tidskriftsartikel (refereegranskat)abstract
    • The impact of electrical current on the structure of single free-standing Be-doped GaAs nanowires grown on a Si 111 substrate is investigated. Single nanowires have been structurally analyzed by X-ray nanodiffraction using synchrotron radiation before and after the application of an electrical current. The conductivity measurements on single nanowires in their as-grown geometry have been realized via W-probes installed inside a dual-beam focused ion beam/scanning electron microscopy chamber. Comparing reciprocal space maps of the 111 Bragg reflection, extracted perpendicular to the nanowire growth axis before and after the conductivity measurement, the structural impact of the electrical current is evidenced, including deformation of the hexagonal nanowire cross section, tilting, and bending with respect to the substrate normal. For electrical current densities below 30 A mm−2, the induced changes in the reciprocal space maps are negligible. However, for a current density of 347 A mm−2, the diffraction pattern is completely distorted. The mean cross section of the illuminated nanowire volume is reconstructed from the reciprocal space maps before and after the application of electrical current. Interestingly, the elongation of two pairs of opposing side facets accompanied by shrinkage of the third pair of facets is found. The variations in the nanowire diameter, as well as their tilt and bending, are confirmed by scanning electron microscopy. To explain these findings, material melting due to Joule heating during voltage/current application accompanied by anisotropic deformations induced by the W-probe is suggested.
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21.
  • Barzegar, Hamid Reza, et al. (författare)
  • Synthesis of graphene nanoribbons inside boron nitride nanotubes
  • 2016
  • Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 253:12, s. 2377-2379
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on bottom-up synthesis of graphene nanoribbons inside boron nitride nanotubes, using coronene molecules as building blocks. The synthesized ribbons are one or two coronene molecules wide, depending on the diameter of the host nanotube. The encapsulated carbon nanostructures can be eliminated from the inner cavity of the filled boron nitride nanotube via oxidation without any damage to the nanotube structure.
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22.
  • Becker, Chandler A., et al. (författare)
  • Thermodynamic modelling of liquids : CALPHAD approaches and contributions from statistical physics
  • 2014
  • Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 251:1, s. 33-52
  • Tidskriftsartikel (refereegranskat)abstract
    • We describe current approaches to thermodynamic modelling of liquids for the CALPHAD method, the use of available experimental methods and results in this type of modelling, and considerations in the use of atomic-scale simulation methods to inform a CALPHAD approach. We begin with an overview of the formalism currently used in CALPHAD to describe the temperature dependence of the liquid Gibbs free energy and outline opportunities for improvement by reviewing the current physical understanding of the liquid. Brief descriptions of experimental methods for extracting high-temperature data on liquids and the preparation of undercooled liquid samples are presented. Properties of a well-determined substance, B-2 O-3, including the glass transition, are then discussed in detail to emphasize specific modelling requirements for the liquid. We then examine the two-state model proposed for CALPHAD in detail and compare results with experiment and theory, where available. We further examine the contributions of atomic-scale methods to the understanding of liquids and their potential for supplementing available data. We discuss molecular dynamics (MD) and Monte Carlo methods that employ atomic interactions from classical interatomic potentials, as well as contributions from ab initio MD. We conclude with a summary of our findings.
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23.
  • Beenken, W J D, et al. (författare)
  • Excited state properties of neutral and charged ter-fluorene with and without a keto-defect
  • 2008
  • Ingår i: Physica Status Solidi. B: Basic Research. - : Wiley. - 0370-1972. ; 245:5, s. 849-853
  • Tidskriftsartikel (refereegranskat)abstract
    • Stimulated by the recent experimental report of optical properties of charged oligofluorenes [S. Fratiloiu et al., J. Phys. Chem. B 210, 59845993 (2006)], we have used time-dependent density functional theory (TD-DFT) to study the electronic structure of neutral and charged ter-fluorene with and without keto-defect. We have characterized the excited states by site- and space-based representations of the density matrix. For the defectless neutral species we found typical excitons, while the first excited states of the corresponding charged species represent long-range oscillations of the electron or hole along the whole oligomer. For the neutral ketonized ter-fluorene we found trapping of the excited electron. Similarly, the unpaired electron of the anion ground' state is trapped. The excited state properties of the cation; however, are insensitive to the keto-defect.
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24.
  • Benavides, Vicente, et al. (författare)
  • Raman and electron microscopy study of C60 collapse/transformation to a nanoclustered graphene-based disordered carbon phase at high pressure/temperature
  • 2015
  • Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 252:11, s. 2626-2629
  • Tidskriftsartikel (refereegranskat)abstract
    • Transformation of C60 polymers to a superelastic hard carbon (nanoclustered graphene phase (NGP)) occurring in metal matrix at 5 GPa in a temperature interval of 1000–1100 K was studied by optical, scanning electron microscopy (SEM), and Raman spectroscopy. Raman spectral scan across the sample surface allowed us to identify different stages of the structural transformation. The SEM and Raman spectroscopy data testify for the NGP appearance at the defects concentration sites in the parent fullerite structure. We propose that the buckyballs collapse/formation of the NGP is governed by nucleation and growth (diffusive) mechanism unlike earlier discussed in the literature possibility of the martensitic-type (displacive) character of this transformation.
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25.
  • Bhandary, Sumanta, et al. (författare)
  • Quasiperiodic Van der Waals Heterostructures of Graphene and Hexagonal Boron Nitride
  • 2022
  • Ingår i: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. ; 259:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Advancement toward opening a bandgap at the Dirac point induced by symmetry breaking paved the way to realize 2D heterostructures with graphene and hexagonal boron nitride (h-BN). An alternate arrangement of graphene and h-BN layers in a 3D stacking can tune the bandgaps of these composites depending on the position of B and N atoms with respect to C atoms of graphene. Herein, a unique possibility of arranging graphene and h-BN atomic layers in a quasiperiodic Fibonacci sequence to study the possibilities of controlling the electronic properties of these heterostructures is explored. Density functional theory calculations combined with van der Waals corrections reveal that these quasiperiodic heterostructures are more stable than normal periodic stacking of monolayers of graphene and h-BN. Moreover, for certain arrangements of atomic layers, sizeable bandgaps can be obtained.
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26.
  • Bidermane, Ieva, 1984-, et al. (författare)
  • Characterization of Gas Phase of Iron Phthalocyanine with X-ray Photoelectron and Absorption Spectroscopies
  • 2015
  • Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 252:6, s. 1259-1265
  • Tidskriftsartikel (refereegranskat)abstract
    • Despite the numerous studies dedicated to phthalocyanine molecules adsorbed on surfaces, in monolayer or thin film, very few works have been focused on the characterization of vapors of these molecules. In this article we present the C 1s, N 1s and Fe 2p photoemission results as well as N K-edge X-ray absorption data of iron phthalocyanine (FePc) in gas phase. Presented comparison of X-ray photoelectron spectroscopy and X-ray absorption spectroscopy spectra of FePc films show a great similarity with the gas phase results, confirming the molecular character of thick films. The Fe2p photoemission spectrum of the gas phase FePc, shown for the first time, can be considered as a fingerprint of the Fe(II) ionic state of the central metal of the iron phthalocyanine. The performed multiplet calculations for describing the Fe 2p XP spectrum indicate 3Eg (a1g2eg32g1) state as the most probable ground state for thick film of iron phthalocyanine.
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27.
  • Bigdeli, Sedigheh, et al. (författare)
  • New description of metastable hcp phase for unaries Fe and Mn: Coupling between first-principles calculations and CALPHAD modeling
  • 2016
  • Ingår i: Physica Status Solidi B. - : John Wiley & Sons. - 1521-3951 .- 0370-1972. ; :9, s. 1830-1836
  • Tidskriftsartikel (refereegranskat)abstract
    • The main focus in developing the third generation of CALPHADdatabases is to model thermodynamic properties of materialsby using models which are more physically based andvalid down to 0K. First-principles calculations are helpful tochoose and validate those models. Reliable calculation results,for example, at very low temperatures or on metastable systemsreveal physical facts which might be inaccessible by experiments.Following our earlierwork for modeling thermodynamicproperties of pure elements (i.e., Fe and Mn) in third-generationCALPHAD databases, the (hcp) phase was modeled as ametastable phase in the present work. Although hcp phase isjust observed in these two elements under ultra-high pressure, inthe binary Fe–Mn this phase is metastable at ambient temperaturesand pressures. Therefore, it should be properly modeled inunaries for later optimization of binary systems. Based on densityfunctional theory (DFT) calculations, the magnetic groundstate and the magnetic properties of -Fe, -Mn, and their binarysolution phase were calculated. It was found that -Fe is antiferromagnetic(type II) while -Mn has a paramagnetic groundstate. Accordingly, magnetic contributions to thermodynamicproperties were accurately modeled. Moreover, by means ofthe extrapolation of experimental data for the thermodynamicproperties of binary systems and high-pressure data for unaries,the metastable hcp phases at ambient pressure were modeledfor the third-generation CALPHAD database, consistently withother stable phases in the elements Fe and Mn.
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28.
  • Bigdeli, Sedigheh, et al. (författare)
  • On the third-generation Calphad databases : An updated description of Mn
  • 2015
  • Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 252:10, s. 2199-2208
  • Tidskriftsartikel (refereegranskat)abstract
    • Aiming for better extrapolations and predictabilities of thermodynamic properties of materials, new thermodynamic models are implemented in the third-generation Calphad databases. In these models, each term contributing to the Gibbs energy has an explicit physical meaning. Furthermore, descriptions of thermodynamic properties of materials are valid from 0K up to high temperatures far above the melting point. As a starting point for the development of large self-consistent third-generation database, the new models in the present work are applied to the unary manganese system. Taking into account both the calculated first principles results and experimental data, thermodynamic model parameters are evaluated. Thermodynamic properties predicted using this description, agree very well with available data. The calculated properties vary smoothly in the whole temperature range, which is another important improvement compared to the second-generation databases.
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29.
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30.
  • Blom, Anders, et al. (författare)
  • Resonant states in doped quantum wells
  • 2003
  • Ingår i: Physica Status Solidi. B: Basic Research. - : Wiley. - 0370-1972. ; 235:1, s. 85-88
  • Tidskriftsartikel (refereegranskat)abstract
    • Resonant states can have an important influence on the electronic transport, noise and optical properties of heterostructure devices. We have used a non-variational method to study the resonant states formed by shallow donors inside and outside of quantum wells. The method allows us the evaluation of the position and the width (lifetime) of the resonant states and also of matrix elements such as optical transition probabilities. When the width is compared to results from the approach of resolvent operators, a quantitative difference is found, which we attribute to the neglected intraband scattering in the latter method. We also show how the impurity states, localized and resonant, evolve as the donor is moved into the quantum well from an originally infinite distance.
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31.
  • Borisov, Vladislav, et al. (författare)
  • Microscopic Modeling of Correlated Systems Under Pressure : Representative Examples
  • 2019
  • Ingår i: physica status solidi (b). - : Wiley. - 0370-1972 .- 1521-3951. ; 256:9
  • Tidskriftsartikel (refereegranskat)abstract
    • The complex interplay between different order parameters in correlated systems can be finely tuned by mechanical pressure giving access to a variety of distinct phases and thereby providing new functionalities. This review addresses the challenges in the state-of-the-art theoretical simulations of pressure-induced phenomena on a few representative examples of correlated systems that are currently in the focus of on-going contemporary research. These include organic charge-transfer multiferroics, unconventional iron-based superconductors, frustrated quantum magnets, and candidate systems for Kitaev physics. All these systems show pronounced structural response to moderate pressures or even structural transitions to new phases which can be successfully addressed from first principles. The simulation techniques and general trends in pressure effects are discussed for each material class.
  •  
32.
  • Botella, Pablo, et al. (författare)
  • Single-Walled Carbon Nanotubes Shock-Compressed to 0.5 Mbar
  • 2017
  • Ingår i: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. ; 254:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Single-walled carbon nanotubes (SWCNTs) have been dynamically (shock) compressed to 0.5 Mbar, above the limit of their structural integrity. Two distinct types of material are identified by high-resolution transmission electron microscopy (HRTEM) and multi-wavelength Raman spectroscopy in the sample recovered after shock: multi-layer graphene (MLG) and a two-phase material composed of nano-clustered graphene and amorphous carbon whereas no diamond-like carbon or carbon nano-onions are found. Peak decomposition of the Raman spectra was used to estimate the coherent scatterers (clusters) size in MLG at 36 nm from the D- to G-band intensity ratio dependence on the photon excitation energy. Botella et al. (article no. 1700315) propose the peak fitting model for decomposition of the Raman spectra of highly disordered carbon material containing graphene nano-clusters and stress the importance of accounting for heptagonal- and pentagonal-ring defects in graphene layers for the analysis of such spectra. The cover image shows HRTEM images and the correspondent Raman spectra of the two types of material along with peak decomposition of the two-phase material with the peaks assigned to heptagons (a) and pentagons (b). Particulars of the SWCNTs transformation to other structural forms of carbon at high pressure/temperature are discussed
  •  
33.
  • Botella, Pablo, et al. (författare)
  • Single-Walled Carbon Nanotubes Shock-Compressed to 0.5 Mbar
  • 2017
  • Ingår i: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. ; 254:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Single-walled carbon nanotubes (SWCNTs) have been dynamically (shock) compressed to 0.5 Mbar, above the limit of their structural integrity. Two distinct types of material are identified by high-resolution transmission electron microscopy (HRTEM) and multi-wavelength Raman spectroscopy in the sample recovered after shock: multi-layer graphene (MLG) and a two-phase material composed of nano-clustered graphene and amorphous carbon whereas no diamond-like carbon or carbon nano-onions are found. Peak decomposition of the Raman spectra was used to estimate the coherent scatterers (clusters) size in MLG at 36 nm from the D- to G-band intensity ratio dependence on the photon excitation energy. Botella et al. (article no. 1700315) propose the peak fitting model for decomposition of the Raman spectra of highly disordered carbon material containing graphene nano-clusters and stress the importance of accounting for heptagonal- and pentagonal-ring defects in graphene layers for the analysis of such spectra. The cover image shows HRTEM images and the correspondent Raman spectra of the two types of material along with peak decomposition of the two-phase material with the peaks assigned to heptagons (a) and pentagons (b). Particulars of the SWCNTs transformation to other structural forms of carbon at high pressure/temperature are discussed
  •  
34.
  • Briddon, Patrick, et al. (författare)
  • Accurate Kohn–Sham DFT with the speed of tight binding : Current techniques and future directions in materials modelling
  • 2011
  • Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 248:6, s. 1309-1318
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a review of methodological and implementation details of the AIMPRO Kohn–Sham density functional code. It is demonstrated that full Kohn–Sham density functional theory calculations can be performed in a time only marginally greater than tight binding implementations and a route is opened to achieve full and demonstrable convergence with respect to basis size. Topics covered will include both the kernel and functionality of the current code, a discussion of recent developments as well as future research directions and perspectives. Also, a broad discussion regarding the application of these methods is made that, it is hoped, will serve as a useful guide to application specialists.
  •  
35.
  • Briones-Leon, Antonio, et al. (författare)
  • Orbital and spin magnetic moments of ferrocene encapsulated in metallicity sorted single-walled carbon nanotubes
  • 2012
  • Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlag Berlin. - 0370-1972 .- 1521-3951. ; 249:12, s. 2424-2427
  • Tidskriftsartikel (refereegranskat)abstract
    • The nature of the electronic and local magnetic properties of ferrocene (FeCp2) filled single-walled carbon nanotubes (SWCNT) has been investigated by X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD). Metallic, semiconducting, and unsorted ferrocene-filled tubes have been studied in different conditions of temperature and magnetic field. XMCD signal becomes evident with the application of a magnetic field at low temperature. We find that the molecular states of ferrocene interact with SWCNT of different metallicities. A paramagnetic behavior of encapsulated ferrocene is observed from the magnetic field dependent XMCD measurements which is consistent with theoretical predictions.
  •  
36.
  • Carvalho, Alexandra, et al. (författare)
  • Boron doped Si nanoparticles : the effect of oxidation
  • 2013
  • Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 250:9, s. 1799-1803
  • Tidskriftsartikel (refereegranskat)abstract
    • The preferred location of boron in oxidized free-standing Si nanoparticles was investigated using a first-principles density functional approach. The nanoparticles were modeled by a silicon core about 1.5 nm in diameter surrounded by an outer shell of SiO2 with a thickness of about 0.5 nm, and considered negatively charged. The calculated formation energies indicate that B is equally stable in the Si core and in the SiO2 shell, showing preference for interface sites. This indicates that, in contrast with phosphorus, the ratio of the boron concentration in the silicon core to that of the silicon shell will not be improved over one upon thermal annealing.
  •  
37.
  • Chen, H.Q., et al. (författare)
  • Critical behavior of vortices in epitaxial Tl-2201 films at zero external field
  • 2004
  • Ingår i: PHYSICA STATUS SOLIDI B-BASIC RESEARCH. - : Wiley. - 0370-1972 .- 1521-3951. ; 241:15, s. 3556-3562
  • Tidskriftsartikel (refereegranskat)abstract
    • The resistive transition and current–voltage characteristics of a Tl-2201 superconducting microbridge are measured close to the critical temperature in zero external magnetic field. The dissipation mechanism is studied by analyzing dV/dI and power dissipation P(= IV) as functions of transport current. The Jc–T curves exhibit three distinct types of behavior depending on temperature. In the low temperature regime, the critical current density is proportional to (1 – T/Tc). At intermediate temperatures, thermally activated flux creep dominates and Jc is proportional to 1 – n(T/Tc) – m(T/Tc)2. In the high temperature regime, Jc is equal to the G–L depairing current. The depinning current, Jc1, is determined, taking into account thermally activated flux motion and flux motion induced by the transport current. Jc1 depends linearly on temperature and vanishes at 82 K, Jc1 = Jc1(0) (1 – T/Tc1).
  •  
38.
  • Chen, Rongzhen, et al. (författare)
  • Exploring the electronic and optical properties of Cu2Sn1-xGexS3 and Cu2Sn1-xSixS3 (x = 0, 0.5, and 1)
  • 2017
  • Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951.
  • Tidskriftsartikel (refereegranskat)abstract
    • To accelerate environmental friendly thin-film photovoltaic technologies, earth-abundant, non-toxic, and low-cost materials are demanded. We study the compounds of Cu2Sn1−xGexS3 and Cu2Sn1−xSixS3 (x = 0, 0.5, and 1) employing first-principles method within the density functional theory. The compounds have comparable band dispersions. The band-gap energies Eg can be tailored by cation alloying the Sn atoms with Ge or Si. The gap energies of Cu2Sn1−xGexS3 and Cu2Sn1−xSixS3, with x = 0, 0.5, and 1, vary almost linearly from 0.83 to 1.43 eV and 2.60 eV, respectively. However, the gap energy of Cu2SiS3 does not follow the linear relation for x > 0.8. The effective electron masses at the Γ-point of the lowest conduction band are almost isotropic for all materials, which are between 0.15m0 and 0.25m0. On the other hand, the effective hole masses of the topmost valence band show very strong anisotropy for all compounds. In the (010) direction, the hole masses are estimated to be between 1.01m0 and 1.85m0, while between 0.11m0 and 0.41m0 in the (001) direction. Calculations reveal that all compounds have high absorption coefficients that are comparable with that of Cu2ZnSnS4. The absorptions in the energy region from Eg + 0.5 eV to Eg + 1.0 eV are even higher for Ge- and Si-alloying of Cu2SnS3, compared with Cu2ZnSnS4. The high-frequency dielectric constants of the compounds are between 6.8 and 8.9. Cu2Sn1−xGexS3 and Cu2Sn1−xSixS3 can be considered as potential candidates for absorber materials in thin-film solar cells.
  •  
39.
  • Chen, Shula, et al. (författare)
  • Long delays of light in ZnO caused by exciton-polariton propagation
  • 2012
  • Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlagsgesellschaft. - 0370-1972 .- 1521-3951. ; 249:7, s. 1307-1311
  • Tidskriftsartikel (refereegranskat)abstract
    • We study the propagation of exciton-polaritons through bulk ZnO using time-resolved photoluminescence (PL) complemented by time-of-flight measurements of laser pulses. When the photon energy approaches donor bound exciton resonances, substantial time delays in PL light propagation are observed which reach up to 210 ps for a 0.55 mm thick crystal. By comparing results from time-of-flight measurements performed using PL light and laser pulses, the observed delay is shown to be due to the formation of exciton-polaritons and their spectral dispersion. It is also shown that the main contribution to the slow-down effect arises from free exciton-polaritons, whereas bound exciton-polaritons become important only in close vicinity to the corresponding resonances.
  •  
40.
  • Chen, Xiren, et al. (författare)
  • Bi-Induced Electron Concentration Enhancement Being Responsible for Photoluminescence Blueshift and Broadening in InAs Films
  • 2019
  • Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 256:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Photoluminescence (PL) study is conducted on InAs films molecular beam epitaxially grown on GaAs substrates with different Bi flux levels. A PL peak blueshift accompanied by linewidth broadening is found with the increase of Bi/As flux ratio, in contrast to the common Bi isoelectronic incorporation or surfactant effect. It is, with detailed lineshape analysis and the evidence of PL peak splitting in a magnetic filed, attributed to the electron concentration enhancement induced by Bi flux. The electron concentration in InAs film is evaluated, which is about 5-fold enhanced as Bi/As flux ratio rises up from 0 to 1x10(-3). The temperature dependence of the PL spectrum indicates that the carrier redistribution augments while the carrier-phonon Frohlich scattering weakens in InAs films with high Bi/As flux ratios. These findings reveal a novel Bi effect of electron concentration enhancement, and contribute to the basic knowledge of Bi in III-V semiconductors.
  •  
41.
  • Chen, Xingxing, et al. (författare)
  • Control of fluorescence enhancement and directionality upon excitations in a thin-film system
  • 2015
  • Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 252:10, s. 2222-2229
  • Tidskriftsartikel (refereegranskat)abstract
    • Nanostructures with various configurations have been extensively used to engineer the emission properties of embedded fluorophores, but lack the flexibility to dynamically control fluorescence. Here we report a thin-film cavity system, comprising a quarter wavelength thick dye-doped dielectric coating on a reflecting surface, in which the fluorescence enhancement and directionality can be significantly modified by altering the illumination angle. The configuration of the cavity yields absorption properties that are highly dependent on illumination angles, due to the coupling between molecular absorption and Fabry-Perot resonances. Therefore the fluorescence intensity relating to the angle-dependent absorbing efficiency varies with illumination angles. In addition, as a result of synergy between intrinsic absorption of the reflecting surface, Fabry-Perot and surface-plasmon-polariton resonances and illumination-angle dependent excitation efficiencies for differently located molecules, the global emission intensity, including emission from dyes at all locations, can be directionally redistributed by altering the illumination angle.
  •  
42.
  • Cholewa, Marian, et al. (författare)
  • Investigating the Secondary Electron Emission of Nanomaterials Induced by a High-Resolution Proton Beam
  • 2022
  • Ingår i: Physica Status Solidi (B). - : Wiley. - 0370-1972 .- 1521-3951.
  • Tidskriftsartikel (refereegranskat)abstract
    • Herein, the secondary electron emission (SEE) from 1D nanomaterials in the form of nanorods is investigated. The small beam of a 1.5 MeV +H2 hydrogen with a sub 70 nm in diameter allows studying the SEE with a very high resolution. A wide range of nanomaterials from various laboratories are studied, including thin ZnO and ZnO/GaN nanostructures grown on 1 μm thick Si3N4 membranes and thick InP, GaN and GaN/AlN nanorod structures grown on bulk Si substrates. By virtue of the small size of the exciting nanobeams, high-resolution maps could be created presenting an SEE yield from various parts of the structures. This allows us to show that the top parts of nanorods in ZnO, ZnO/GaN, GaN, InP, and GaN/AlN nanostructures emit secondary electrons much more efficiently than the valley areas between nanorods. These results indicate that by a proper design and growth of 1D nanostructures, SEE properties could be improved over those of the traditionally used Au and CsI thin films. This work has been undertaken to find materials with the highest achievable SEE emission, which is a figure of merit for the detection efficiency relevant for the development and application of novel radiation detectors.
  •  
43.
  • Darakchieva, Vanya, et al. (författare)
  • Assessment of phonon mode characteristics via infrared spectroscopic ellipsometry on a-plane GaN
  • 2006
  • Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 243:7, s. 1594-1598
  • Tidskriftsartikel (refereegranskat)abstract
    • Generalized infrared spectroscopic ellipsometry was applied to study the vibrational properties of anisotropically strained a-plane GaN films with different thicknesses. We have established a correlation between the phonon mode parameters and the strain, which allows the determination of the deformation potentials and strain-free frequency of the GaN A,(TO) mode. These results are compared with previous theoretical and experimental findings and discussed.
  •  
44.
  •  
45.
  • Dash, Saroj Prasad, 1975, et al. (författare)
  • Initial stages of growth of iron on silicon for spin injection through Schottky barrier
  • 2011
  • Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 248:10, s. 2300-2304
  • Tidskriftsartikel (refereegranskat)abstract
    • The characterization of ferromagnet-semiconductor interfaces with monolayer (ML) depth resolution is an important issue in the development of spin injection devices. In this article, highly resolved depth distributions of Fe have been measured during the initial stages of growth of Fe on Si (100) at room temperature by in situ high-resolution Rutherford backscattering spectrometry. Extensive in-diffusion of Fe has been observed even for the coverage of 0.0325 ML of Fe. At this coverage the Si crystal structure is apparently still conserved. Every second Si layer is depleted of Fe, thus giving rise to compositional oscillations of Fe. At higher coverages strong interdiffusion occurs resulting in the formation of silicides at the interface. Even at 9.2 ML of Fe coverage, no pure Fe layers were observed.
  •  
46.
  • Delgado Carrascon, Rosalia, et al. (författare)
  • Optimization of GaN Nanowires Reformation Process by Metalorganic Chemical Vapor Deposition for Device-Quality GaN Templates
  • 2020
  • Ingår i: Physica Status Solidi (B) Basic Research. - : Wiley. - 0370-1972 .- 1521-3951. ; 257:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Herein, the potential of reformed GaN nanowires (NWs) fabricated by metalorganic chemical vapor deposition (MOCVD) for device-quality low-defect density templates and low-cost alternative to bulk GaN substrates is demonstrated. The effects of epilayer thickness and NW reformation conditions on the crystalline quality and thermal conductivity of the subsequent GaN epilayers are investigated. Smooth surfaces with atomically step-like morphologies with no spirals are achieved for GaN epilayers on the reformed NW templates, indicating step-flow growth mode. It is further found that annealing of the NWs at a temperature of 1030 °C in the presence of NH3 and H2, followed by a coalescence done at the same temperature under planar growth conditions, leads to the most efficient screw dislocation density reduction by nearly an order of magnitude. At these optimized conditions, the growth takes place in a layer-by-layer fashion, producing a smooth surface with a root mean square (RMS) roughness of 0.12 nm. The highest thermal conductivity of k = 206 W m−1 K−1, approaching the respective value of bulk GaN, is obtained for the optimized 2 μm-thick GaN layer. The thermal conductivity results are further discussed in terms of the phonon-dislocation and the phonon-boundary scattering.
  •  
47.
  • Dhanabalan, D., et al. (författare)
  • Studies on Schottky Barrier Diodes Fabricated using Single-Crystal Wafers of β-Ga2O3 Grown by the Optical Floating Zone Technique
  • 2022
  • Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 259:2
  • Tidskriftsartikel (refereegranskat)abstract
    • β-Ga2O3 is one of the most promising wide-bandgap materials for optoelectronic applications as well as a conducting substrate for GaN-based device technologies. Single crystals of undoped β-Ga2O3 are grown by the optical floating zone technique utilizing compressed dry air as growth atmosphere. The properties of β-Ga2O3 are highly anisotropic. Optimization of the processing recipe for wafers along different orientations suitable for device development is conducted. Structural, optical, and electrical properties of the wafers are determined. Efforts are made to fabricate Schottky diodes based on Pt/Ti/Au–β-Ga2O3–Ti/Au device structures. Devices are fabricated on (−201) cut wafers. The device characteristics are discussed in detail.
  •  
48.
  • Dou, Cheng, et al. (författare)
  • Photoluminescence Evolution with Deposition Thickness of Ge Nanostructures Embedded in GaSb
  • 2022
  • Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 259:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Herein, low-temperature and temperature-dependent photoluminescence (PL) measurements are carried out on highly tensile-strained Ge nanostructures embedded in GaSb matrix, and the effects of Ge deposition thickness are clarified. The direct-gap transition-related PL feature is successfully identified in the tensile-strained Ge nanostructures. While typical PL thermal quenching is observed for the tensile-strained Ge- and GaSb-related transitions in the samples with a Ge deposition being thinner than the critical thickness, a negative thermal quenching shows up for the GaSb interband transition in the samples with Ge deposition surpassing the critical thickness at which high-density nanoparticles form to relax the strain. A phenomenological thermal-injection model is established of electrons from the tensile-strained Ge layer to the GaSb matrix, the thermal quenching is accounted for, and a ladder-like function of the strain-relaxed Ge is clarified to favor the electron activation. The understanding of the effects of deposition thickness is helpful for the high-performance Ge-based light source for optoelectronic integration.
  •  
49.
  • Doyle, Catherine M., et al. (författare)
  • Surface Mediated Synthesis of 2D Covalent Organic Networks : 1,3,5-Tris(4-bromophenyl)benzene on Au(111)
  • 2019
  • Ingår i: Physica Status Solidi (B) Basic Research. - : Wiley. - 0370-1972. ; 256:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Covalent organic networks derived from surface-mediated self-assembly of 1,3,5-tris(4-bromophenyl)benzene into two-dimensional networks on Au(111) have been studied by scanning tunneling microscopy (STM) and by X-ray spectroscopic methods. High resolution soft X-ray photoemission spectroscopy (SXPS) using synchrotron radiation have been used to study the formation of the 1,3,5-tris(4-bromophenyl)benzene-derived 2D networks by observing temperature-dependent C 1s and Br 3d core level XPS spectra. X-ray absorption (XA) measurements of the formation of these 2D networks have been obtained at the C K-edge where their temperature and angular dependence are examined. The results of these XPS and XA spectroscopic measurements are compared to detailed ab initio electronic structure calculations of 1,3,5-tris(4-bromophenyl)benzene molecules to aid the interpretation of the features of these spectra.
  •  
50.
  • Duc Tran, Thien, et al. (författare)
  • Electronic properties of defects in high-fluence electron irradiated bulk GaN
  • 2016
  • Ingår i: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. ; 253:3, s. 521-526
  • Tidskriftsartikel (refereegranskat)abstract
    • Using deep level transient spectroscopy, deep levels and capture cross sections of defects introduced by high-fluence electron irradiation of thick halide vapour phase epitaxy grown GaN has been studied. After irradiation with 2 MeV electrons to a high-fluence of 5×1016 cm-2, four deep trap levels, labelled T1 (EC – 0.13 eV), T2 (EC – 0.18 eV), T3 (EC – 0.26 eV) T4 and a broad band of peaks consisting of at least two levels could be observed. These defects, except T1 and T3, were annealed out after annealing at 650 K for 2 hours. The capture cross section is found to be temperature independent for T2 and T3, while T1 shows an decresing capture cross section with increasing temperature, suggesting that electron capturing to this deep level is governed by a cascade capturing process.
  •  
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