Physik: DPG Tagungen - Sitzung O 28 - Nano-science.de

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Physik: DPG Tagungen - Sitzung O 28 http://www.dpg-tagungen.de/archive/2004/o_28.html optical spectra are determined in the independent-particle approximation from all-electron wave functions obtained by the projector-augmented wave (PAW) method. [1] T. Yasuda et al., Phys. Rev. Lett. 74, 1995, 3431; R. Shioda, J. van der Weide, Phys. Rev. B 57, 1998, R6823; W.G. Schmidt, F. Bechstedt, J. Bernholc, Phys. Rev. B 2001, 63, 5322. [2] C.A. Hacker, R.J. Hamers, J. Phys. Chem. B 107, 2003, 7689; T. Yasuda et al., Phys. Rev. Lett. 87, 2001, 037403. O 28.21 Poster Mi 16:00 Bereich C Rauheit und Schädigung einer GaAs-Oberfläche nach dem chemisch unterstützten Ionenstrahlätzen mit Cl 2 /Ar + •Jens Dienelt, Klaus Zimmer, Justus von Sonntag und Bernd Rauschenbach Leibniz-Institut für Oberflächenmodifizierung (IOM), Permoserstr. 15, 04318 Leipzig Die chemische und die physikalische Abtragskomponente während des chemisch unterstützten Ionenstrahlätzens (CAIBE) von GaAs mit Cl 2 /Ar + bewirkt sehr unterschiedliche Einflüsse auf die Rauheit und die Schädigung des oberflächennahen Bereiches. Die Charakteristik der Einzelprozesse spiegelt sich direkt in der Oberflächenrauheit wieder. Der starke chemische Ätzangriff von Chlorgas auf die GaAs-Oberfläche zeigt eine ausgeprägte Anisotropie der Ätzprofilentwicklung, wobei die {111}-Ebenen durch deren geringe Ätzrate den Abtragsprozess maß geblich beeinflussen. Neben der Temperatur oder dem Chlordruck hat demnach auch die Kristallorientierung einen großen Einfluss auf die Oberflächenrauheit. Beim reinen Zerstäubungsprozess ergeben sich aufgrund der Impuls- und Energieübertragung des gerichteten Ionenbeschusses die glattesten Oberflächen. Im Gegensatz zur geringen Oberflächenrauheit wird bei der Zerstäubung der oberflächennahe Bereich jedoch am stärksten geschädigt. Hierzu werden ortsaufgelöste Photolumineszenz-Untersuchungen an Mehrfach-Quantentrog-Strukturen aus Al 0,35 Ga 0,65 As/GaAs gezeigt, die unter Anwendung der Schrägschlifftechnik präpariert wurden. O 28.22 Poster Mi 16:00 Bereich C Structural, electronic and spin properties of In nanowires on Si(111) surface •Xóchitl López 1,2 , Anna Krivosheeva 1 , Friedhelm Bechstedt 1 , Jürgen Furtmüller 1 und Andrey Stekolnikov 1 1 Institut für Festkörpertheorie und Theoretische Optik, FSU Jena, Max-Wien-Platz 1, 07743 Jena 2 Instituto de Física, Universidad Autónoma de Puebla, Apartado Postal J-48, Puebla 72570, México In the last years the electronic and structural properties of the indium-induced (4×1), (4×2) and (8×2) surface reconstructions on Si(111) have been intensively studied due to the potential applications on novel optoelectronics devices. In this work the electronic structure calculations are performed using density functional theory in the generalized-gradient approximation and ultrasoft pseudopotentials. The atomic positions were taken from a previous calculations [1], which are consistent with experimental data. The electronic band structures with and without spin polarization are calculated and discussed with respect to the metallic/insulating character of the chains. Because the spin density distribution on these systems might be important for their electronic properties, we study the influence of the spin polarization on the atomic structure and electronic states of the In nanowires on Si(111). Several initial spin configurations are taken into account for all the surface reconstructions in order to observe a magnetic ordering. We acknowledge the partial financial support from CONACyT grants No.36651-E and 36764-E. [1] F. Bechstedt et al., Phys Rev B 68, 1934XX (2003). O 28.23 Poster Mi 16:00 Bereich C Ultrathin layers of Ag deposited on 4H-SiC(0001) •Serguei Soubatch und Ulrich Starke 8 of 32 07.06.2009 22:14
Physik: DPG Tagungen - Sitzung O 28 http://www.dpg-tagungen.de/archive/2004/o_28.html Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, 70569 Stuttgart Despite the significance of SiC for high-temperature and high-power electronic devices based on metal/semiconductor interfaces, the initial stages of metal layer formation on SiC surfaces still remain insufficiently explored in comparison to well known metal/silicon heterointerfaces, such as Ag on Si. We investigated the deposition of Ag on 4H-SiC(0001) using quantitative low-energy electron diffraction (LEED). Ag layers of 0.2, 0.5 and 1 ML coverage were deposited on the clean (3×3) and (?3×?3)R30 ? SiC(0001) surface phases. The structural development after room temperature deposition as well as after annealing was studied. The (3×3) phase is only marginally influenced by Ag deposition at room temperature. Annealing leads to Ag diffusion and subsequent desorption without a significant phase transformation. In case of the (?3×?3)R30 ? phase considerable changes can be monitored in the LEED intensities spectra immediately after deposition. Here, structural changes are found during annealing also, possibly caused by Ag diffusion. In both cases the original surface phases reappear after Ag desorption. O 28.24 Poster Mi 16:00 Bereich C High temperature stable silicide contacts on the nanometer scale •G. Gardinowski, C. Tegenkamp, T. Block, S. Vagt, V. Zielasek und H. Pfnür Institut für Festkörperphysik, Universität Hannover, Appelstrasse 2, 30167 Hannover In order to characterize nanostructure electrically contacts are essential to build a bridge between the macrospic and the mesoscopic world. High temperature experiments with nanostructures on silicon substrates are particularly interesting, but require contacts which can withstand temperatures up to 1100 ? C without changes in their chemical composition and without interdiffusion at the contact area of the silicide and the silicon. Using electron beam lithography different silicide contacts on both Si(111) and Si(100) surfaces have been fabricated and tested. With regard to the specific formation temperatures for silicides, mainly Mo, Ta and Ti have been tested. All three silicides are stable up to at least 800 ? C. The metallic character of the silicides was tested by masurements of the conductivity. However, for higher temperatures the decomposition of MoSi 2 and TaSi 2 sets in leaving behind rough contact areas. Only the TiSi 2 silicide remains intact, as checked by µ-Auger spectroscopy. Furthermore, after optimization of the lithography parameters, TiSi 2 contact pads with separation lengths of 200 nm were fabricated successfully, i.e. after removing the native oxide from the silicon surface (with pads) by a high temperature annealing step, perfect silicon was found in between the contacts as seen by STM/SEM. The edges of the contacts are rather sharp and well-defined. The transition area was determined to be around 1nm. O 28.25 Poster Mi 16:00 Bereich C Direct evidence from FTIR for hydrogen incorporation into the MOCVD-grown P-rich reconstructed InP(100) surface •Tobias Letzig, H.J. Schimper, Thomas Hannappel und Frank Willig Hahn-Meitner-Institute, Glienicker Str. 100, 14109 Berlin, Germany Recently, the groups of Schmidt and Bechstedt have discussed several different surface reconstructions for InP(100). Three of those have been assigned to actually prepared surface reconstructions. In the case of MOCVD growth the P-rich (2x1/2x2) surface is postulated to contain hydrogen bonds that stabilize buckled P-P dimers. A P-rich surface with a different reconstruction is formed via MBE growth in the absence of hydrogen. The In-rich (2x4) reconstruction also does not contain any hydrogen atoms. We present here experimental support for the postulated hydrogen bonds on the surface of MOCVD grown P-rich (2x1/2x2) reconstructed InP(100) in the form of FTIR spectra that were measured in UHV. We made use of a patented contamination free transfer of the sample from the MOCVD reactor into a mobile UHV chamber. FTIR spectra will be presented for the as-grown surface and for the surface after further exposure to hydrogen and deuterium. O 28.26 Poster Mi 16:00 Bereich C 9 of 32 07.06.2009 22:14
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