AVS 46th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS1+EM-TuA

Paper SS1+EM-TuA5
The Surface Structure of @alpha@-Al@sub 2@O@sub 3@(0001) Studied by LEED

Tuesday, October 26, 1999, 3:20 pm, Room 606

Session: Oxides: Growth and Structure
Presenter: C.F. Walters, Sandia National Laboratories
Authors: C.F. Walters, Sandia National Laboratories
E.A. Soares, Lawrence Berkeley National Laboratory
M.A. Van Hove, Lawrence Berkeley National Laboratory
K.F. McCarty, Sandia National Laboratories
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The surface structure of @alpha@-Al@sub 2@O@sub 3@(0001) has been investigated using normal-incidence low-energy electron diffraction. High quality sapphire samples were produced by ex-situ annealing in air, followed by in-situ cleaning using atomic deuterium at an elevated sample temperature. To investigate the possible occurrence of different surface structures and/or stoichiometries, the samples were processed, subsequent to the atomic deuterium cleaning, using several different procedures. These included annealing the sample in oxygen, and exposing the cooled sample to atomic deuterium. The experimental data were compared to results of calculations performed using an automated tensor LEED program. Several different models were used as the starting point for the analysis. These included termination by: an oxygen layer, a single aluminum layer, a double aluminum layer, and a "hydroxyl" covered single aluminum layer. Additionally, we have analyzed mixtures of these terminations, with the mixtures including different species, as well as the same species but containing different crystallographic planes (i.e., terraced surfaces with fractional unit cell step heights). For each sample preparation, the best structural model was determined via an analysis of the Pendry R-factor that took into account the effect of the additional fitting parameters for the models containing mixed terminations. The best-fit models derived from the tensor LEED analysis will be discussed with respect to the preparation method used, as well as compared to the results of recent first-principles calculations. This work supported by USDOE-OBES-Division of Materials Sciences.