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

Paper SS1+EM-TuA6
Formation of Epitaxial Al@sub 2@O@sub 3@ on Ni@sub 3@Al(111) Studied by STM, HREELS, UPS, @DELTA@@PHI@, and LEED

Tuesday, October 26, 1999, 3:40 pm, Room 606

Session: Oxides: Growth and Structure
Presenter: A. Rosenhahn, Universität Bonn, Germany
Authors: A. Rosenhahn, Universität Bonn, Germany
J. Schneider, Universität Bonn, Germany
J. Kandler, Universität Bonn, Germany
T. Pelster, Universität Bonn, Germany
R. Linke, Eindhoven University of Technology, The Netherlands
C. Becker, Universität Bonn, Germany
K. Wandelt, Universität Bonn, Germany
Correspondent: Click to Email
The formation of oxides on the Ni@sub 3@Al(111) single crystal surface has been studied in the temperature range from 300K to 1000K by STM, HREELS, UPS, @DELTA@@PHI@, and LEED. The experiments reveal a strong temperature dependence of the structure and the chemical composition of the resulting oxides, which is caused mainly by a rising aluminum mobility with increasing temperature. Adsorption of oxygen at room temperature creates a disordered surface which appears rough in STM images and shows a diffuse LEED pattern. At 600K STM images show patches of different appearance on the alloy surface. At low coverages the small oxidic nuclei possess a triangular shape, and HREELS measurements show a Al@sub 2@O@sub 3@-like composition. At higher coverages two areas with different appearance can be distinguished in STM, accompanied by the observation of mixed Ni/Al-oxide vibrations in HREELS. At 800K STM measurements show highly ordered triangular shaped oxidic islands. A moiré structure can be observed which corresponds to a superstructure due to an unrotated single O/Al overlayer, that has also been found by LEED and HREELS measurements. The electronic structure of the film being very similar to that of O/Al(111). Adsorption at 1000K finally leads to the growth of an oxidic film, that proceeds from steps exclusively. The oxide exists in two rotational domains that can be detected in LEED and STM. Both HREELS and UPS measurements show the formation of a Al@sub 2@O@sub 3@-doublelayer. Only at this temperature the chemical order of the underlying Ni@sub 3@Al(111) substrate is completely restored.