[en] Near edge X-ray absorption fine structure (NEXAFS) measurements at the N-K-edge are used to study the effect of 100 keV Si ion implantation in GaN samples grown by ECR-MBE. It is demonstrated that the implantation-induced increase of the static disorder is detectable in the NEXAFS spectra as a broadening of the NEXAFS resonances. In addition to that, implantation introduces two new resonance lines, the RL1 and RL2, in the NEXAFS spectra. The RL1, which appears at 1.7 eV below the absorption edge, is observed in all the implanted samples and is attributed to nitrogen interstitials and/or N antisite defects. The RL2 appears at about 1.0 eV above the absorption edge, when the implantation dose exceeds 1x10¹⁶ cm^-2, and it is attributed to nitrogen dangling bonds created by the implantation. Atomic force microscopy shows that the surface roughness decreases with increasing implantation dose while the overall surface morphology changes significantly after implantation with a dose that causes amorphization

[en] X-ray absorption spectroscopy is a reliable technique to evaluate the hole content n_H in polycrystalline oxide-based high temperature superconductors. For single crystals, the same method can be used by taking into consideration the dependency of the absorption on orientation of the polarization vector in the CuO₂-plane. The polarization i.e. angular dependence of the main and satellite peak at the Cu-L₃ edge of Bi_2-yPb_ySr_2-xLa_xCuO_6+δ (Pb-Bi2201) single crystals was studied by XAS over a wide doping range. The optimum and the underdoped samples show maxima and minima corresponding to the high symmetry lines of the Brillouin zone. The hole content n_H can be determined as angular average. However, in the hole overdoped sample, the peak ratio does not reflect n_H directly. This will be discussed in the context of data on polycrystalline materials. (orig.)

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[en] For β-Ga₂O₃, only little information exists concerning the thermal properties, especially the thermal conductivity λ. Here, the thermal conductivity is measured by applying the electrical 3ω-method on Czochralski-grown β-Ga₂O₃ bulk crystals, which have a thickness of 200 μm and 800 μm. At room temperature (RT), the thermal conductivity along the [100]-direction in Mg-doped electrical insulating and undoped semiconducting β-Ga₂O₃ is confirmed as 13±1 Wm⁻¹K⁻¹ for both crystals. The thermal conductivity increases for decreasing temperature down from 25 K to λ(25 K)=(5.3±0.6)⋅10² Wm⁻¹K⁻¹. The phonon contribution of λ dominates over the electron contribution below RT. The observed function λ(T) is in accord with phonon–phonon–Umklapp scattering and the Debye model for the specific heat at T≳90 K which is about 0.1 times the Debye temperature θ_D. Here, a detailed discussion of the phonon–phonon–Umklapp scattering for T< θ_D is carried out. The influence of point defect scattering is considered for T<100 K. (invited article)

[en] The monoclinic crystal structure of β-${\mathrm{G}\mathrm{a}}_2{\mathrm{O}}_3$ leads to significant anisotropy of the thermal properties. The 2ω-method is used to measure the thermal diffusivity D in [010] and [001] direction respectively and to determine the thermal conductivity values λ of the [100], [010] and [001] direction from the same insulating Mg-doped β-${\mathrm{G}\mathrm{a}}_2{\mathrm{O}}_3$ single crystal. We detect a temperature independent anisotropy factor of both the thermal diffusivity and conductivity values of $D_{[010]}/D_{[001]}={\mathrm{\lambda <!--\; ??\; -->}}_{[010]}/{\mathrm{\lambda <!--\; ??\; -->}}_{[001]}=1.4\pm <!--\; ??\; -->0.1$. The temperature dependence is in accord with phonon–phonon-Umklapp-scattering processes from 300 K down to 150 K. Below 150 K point-defect-scattering lowers the estimated phonon–phonon-Umklapp-scattering values. (paper)

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[en] For single crystalline sulfur-based kesterite Cu₂ZnSnS₄ the electrical and thermal conductivity are measured from 20 K to 320 K. The electrical conductivity decreases exponentially with decreasing temperature. The temperature dependence can be assigned to Mott-variable-range-hopping, an electrical transport process within an impurity band in the band gap. With the 3ω-method a thermal conductivity room temperature value of 5.1 ± 0.5 Wm⁻¹K⁻¹ and a maximal value of 8.0 ± 0.5 Wm⁻¹K⁻¹ at 100 K are found. Phonon-phonon-umklapp-scattering can explain the high temperature range from 100 K to 320 K. The low temperature values of the thermal conductivity are dominated by the temperature-dependence of the specific heat capacity, due to a reduced phonon-mean-free-path, owing to phonon-impurity-scattering. (paper)

[en] TiO₂/V₂O₅ based ceramic materials applied in catalysis were investigated. Structural properties like the grain diameter of these pressed ceramic powders were analysed by means of Rutherford backscattering (RBS) making use of an analytic model to describe the energy spectra of porous rough samples. Grain diameters of these samples were deduced as function of process temperature and chemical composition and related to a phase transition from the TiO₂-Anatase/V₂O₅-Shcherbinaite to Rutile solid solution (Rutile-ss) structure. RBS data were compared to results of scanning electron microscopy (SEM). The activation energy for the sintering at the phase transition was estimated to 5.4 eV.