IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Thursday Sessions
       Session SS1-ThM

Paper SS1-ThM3
Structure, Morphology and Dynamics of High Symmetry AlNiCo-Surfaces

Thursday, November 1, 2001, 9:00 am, Room 121

Session: Quasicrystals
Presenter: W. Theis, Freie Universität Berlin, Germany
Authors: W. Theis, Freie Universität Berlin, Germany
H.R. Sharma, Freie Universität Berlin, Germany
K. Franke, Freie Universität Berlin, Germany
A. Riemann, Freie Universität Berlin, Germany
S. Fölsch, Freie Universität Berlin, Germany
K.H. Rieder, Freie Universität Berlin, Germany
P. Gille, Ludwig-Maximilians-Universität München, Germany
Correspondent: Click to Email
Although many aspects of the bulk structure and dynamics of decagonal quasicrystal are well understood, knowledge regarding their surface structure is much more limited. Employing highly surface sensitive elastic He-atom scattering (HAS) and high resolution low energy electron diffraction (SPA-LEED), we have investigated 10- and 2-fold surfaces of Al@sub 71.8@Ni@sub 14.8@Co@sub 13.4@. The observed SPA-LEED and HAS diffraction patterns reveal that the top most surface layer retains the full symmetry extrapolated from the bulk. Both SPA-LEED and HAS show weak superstructure peaks. In the diffraction patterns of the 2-fold surface we observe extremely weak streaks corresponding to a 16 Å periodicity in addition to the strong peaks reflecting the main 8 Å periodicity. The spots in the odd lines of the diffraction pattern are shifted with respect to the even lines by 0.5 Å@sup -1@. He-atom scattering from the 10-fold surface reveals a low corrugation, extremely few defects, an average terrace width in the order of 100 Å, and a predominant step height of 2 Å. Low temperature (5 K) scanning tunneling microscopy (LT-STM) confirms this step morphology showing a high density of rough 2Å-steps without any tendency towards step pairing and revealing regions of two different surface termination and repeating 5-fold symmetric motives. Surface phonons of the 10-fold surface have been investigated by inelastic He-atom scattering. In experiments with cooled and heated samples and He-atom kinetic energies ranging from 8 to 35meV the (acoustic) Rayleigh mode was observed. Strong single phonon signatures are limited to wavevectors q < 0.5 Å@sup -1@ and the phonon linewidths are resolution limited up to q = 0.25 Å@sup -1@, beyond which they increase rapidly, similar to the behavior recently observed in the corresponding bulk phonons. @footnote 1@ @FootnoteText@ @footnote 1@ F. Dugain, et al, Eur. Phys. J. B. 7, 513 (1999).