Abstract
The structure of the surface has been investigated using low-energy ion scattering, low-energy electron diffraction, and three-dimensional classical scattering simulations. The thermal treatment of the Al films triggered the Al diffusion and reaction to form a clock rotated (001) Pd layer above an ordered Al-Pd underlayer, with a stoichiometry of the top two layers independent of the initial Al coverage. By using a reliability -factor analysis to compare the experimental and simulated azimuthal scans, the lateral clockwise-counterclockwise displacement of the surface Pd atoms was determined to be Å. The driving force for this clock reconstruction is proposed to be the Al-induced interfacial strain. We have also studied the oxygen-induced lifting of the reconstruction. Adsorption of oxygen on the surface at room temperature induces Al segregation and lifts the reconstruction to yield the (1×1) phase. Oxygen removal from the (1×1) surface by higher temperature annealing (∼900 K) was accompanied by depletion of Al from the surface, recovering the reconstruction. The mechanism of a reversible conversion, by O adsorption and by anneal, is discussed.
- Received 3 March 1997
DOI:https://doi.org/10.1103/PhysRevB.56.9894
©1997 American Physical Society