[en] The damage generation of a 3.5 MeV ⁴He⁺ analyzing beam in 4H-SiC during Rutherford backscattering spectrometric (RBS) measurement was studied by channeling effect measurements (RBS/C). A dose rate dependence of the minimum yield (χ_min) was found, i.e., higher damage accumulation occurs with higher dose rate. On the other hand, the dose dependence shows that in the applied dose range (≤3 x 10¹⁷ ions/cm²) there is an effective dose region where χ_min increases with dose, whereas it almost remains unchanged outside of this range. The behavior of analyzing beam induced damage was also discussed according to RBS observations

[en] 4H-SiC single crystalline substrates were implanted at room temperature with 150 keV Al⁺ ions using fluences of 4x10¹⁴, 1x10¹⁵, and 2x10¹⁵ cm^-2 with current density of 2.5 μA cm^-2. The samples were subsequently annealed at 1100 deg. C in N₂ for 1 h in order to analyze their structural recovery. The disorder induced in both sublattices by the Al⁺ ions was studied by backscattering spectrometry in channeling geometry with a 3.5 MeV He²⁺ beam. The results were compared with the optical properties of the samples measured by spectroscopic ellipsometry. In a previous work, we concluded that during the postimplantation annealing of a highly damaged SiC crystalline material the short distance order can be recovered, while the long distance disorder remains. We also presented the possibility to have grains of different polytypes oriented faraway from the original direction. Now, this alternative is confirmed by the cross-sectional transmission and high resolution electron microscopy studies, carried out to obtain information about the crystal structure

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[en] SiC grains can be grown without voids at the SiO₂/Si interface using a simple method, i.e. annealing in CO gas. Present experiments aim to create nucleation centers for the SiC crystallite growth by carbon ion implantation. The formation of the nucleation clusters, as well as the morphology, the size and the density of the nanocrystals, were systematically studied by conventional and high resolution Transmission Electron Microscopy. The nanocrystallites were developed following two different modes of growth: The first develops facets along the <100> crystallographic direction giving tetragonal grains, and the second facets along the <110> direction resulting in elongated nanocrystallites. It was shown that combined low dose carbon implantation and subsequent high temperature annealing in CO leads to a substantial increase of the covering of the Si surface by high quality 3C-SiC nanocrystallites.

[en] The crystallization of amorphous silicon films deposited on glass, using the flash lamp annealing process was realized and studied. The duration of the flash is 20 ms, about two orders of magnitude shorter than the standard rapid thermal annealing process. The a-Si films deposited on Corning glass were irradiated with different energy densities and crystallized exhibiting grains with a mean size up to 6 μm. In order to reduce the strain due to the thermal gradient, the samples were preheated from the backside. The ability of the FLA process to eliminate the ingrain defects in already crystallized poly-Si films at 600 deg. C is also demonstrated

[en] CrSi₂ nanocrystals (NC) were grown by reactive deposition epitaxy of Cr at 550 deg. C. After deposition the Cr is localized in about 20-30 nm dots on the Si surface. The NCs were covered by silicon cap grown by molecular beam epitaxy at 700 deg. C. The redistribution of NCs in the silicon cap was investigated by transmission electron microscopy and atomic force microscopy. The NCs are partly localized at the deposition depth, and partly migrate near the surface. A new migration mechanism of the CrSi₂ NCs is observed, they are transferred from the bulk toward the surface through nanopipes formed in the silicon cap. The redistribution of CrSi₂ NCs strongly depends on Cr deposition rate and on the cap growth temperature.

[en] Under the unified model for active galactic nuclei (AGNs), narrow-line (Type 2) AGNs are, in fact, broad-line (Type 1) AGNs but each with a heavily obscured accretion disk. We would therefore expect the optical continuum emission from Type 2 AGNs to be composed mainly of stellar light and nonvariable on the timescales of months to years. In this work we probe the spectroscopic variability of galaxies and narrow-line AGNs using the multiepoch data in the Sloan Digital Sky Survey Data Release 6. The sample contains 18,435 sources for which there exist pairs of spectroscopic observations (with a maximum separation in time of ∼700 days) covering a wavelength range of 3900-8900 A. To obtain a reliable repeatability measurement between each spectral pair, we consider a number of techniques for spectrophotometric calibration resulting in an improved spectrophotometric calibration of a factor of 2. From these data we find no obvious continuum and emission-line variability in the narrow-line AGNs on average-the spectroscopic variability of the continuum is 0.07 ± 0.26 mag in the g band and, for the emission-line ratios log₁₀([N II]/Hα) and log₁₀([O III]/Hβ), the variability is 0.02 ± 0.03 dex and 0.06 ± 0.08 dex, respectively. From the continuum variability measurement we set an upper limit on the ratio between the flux of the varying spectral component, presumably related to AGN activities, and that of the host galaxy to be ∼30%. We provide the corresponding upper limits for other spectral classes, including those from the BPT diagram, eClass galaxy classification, stars, and quasars.

[en] Semiconducting CrSi₂ nanocrystallites (NCs) were grown by reactive deposition epitaxy. The NCs were covered by 100 nm of epitaxial silicon. Their structure, morphology and optical properties were investigated by transmission electron microscopy (TEM), atomic force microscopy (AFM), ultraviolet photoelectron spectroscopy (UPS) and optical reflectance spectroscopy (ORS). The preservation of the CrSi₂ phase has been justified by UPS, by ORS, and by TEM measurements. The distribution of Cr was investigated by Rutherford backscattering (RBS). The electrically active defects were investigated by deep level transient spectroscopy (DLTS). The crystal structure of the NCs nucleated near the deposition depth is identified by high-resolution TEM as hexagonal CrSi₂. Energy filtered TEM shows that most of the Cr is localized in the three-dimensional (3D) NCs. RBS shows that the concentration of Cr is appropriate for the deposited quantity. In the 0.1 nm Cr sample most of the Cr is localized near the surface; in the 0.6 nm Cr sample the concentration increases at the depth of Cr deposition, while in the 1.5 nm Cr sample the excess Cr is localized near the deposition depth. DLTS Arrhenius plots give activation energies of the defects appropriate for Cr contamination, however these defects may be related to the CrSi₂ NCs

[en] Al, Au, Ti/Al and Ti/Au contacts were prepared on n-GaN and annealed up to 900 deg. C. The structure, phase and morphology were studied by cross-sectional transmission and scanning electron microscopy as well as by X-ray diffraction (XRD), the electrical behaviour by current-voltage measurements. It was obtained that annealing resulted in interdiffusion, lateral diffusion along the surface, alloying and bowling up of the metal layers. The current-voltage characteristics of as-deposited Al and Ti/Al contacts were linear, while the Au and Ti/Au contacts exhibited rectifying behaviour. Except the Ti/Au contact which became linear, the contacts degraded during heat treatment at 900 deg. C. The surface of Au and Ti/Au contacts annealed at 900 deg. C have shown fractal-like structures revealed by scanning electron microscopy. Transmission electron microscopy and XRD investigations of the Ti/Au contact revealed that Au diffused into the n-GaN layer at 900 deg. C. X-ray diffraction examinations showed, that new Ti₂N, Au₂Ga and Ga₃Ti₂ interface phases formed in Ti/Au contact at 900 deg. C, new Ti₂N phase formed in Ti/Al contact at 700 and 900 deg. C, as well as new AlN interface phase developed in Ti/Al contact at 900 deg. C