INTERACTION OF OXYGEN WITH AL(111) AT ELEVATED-TEMPERATURES

The interaction of oxygen with Al(111) was investigated by STM at temp eratures between 350 and 530 K, by annealing an oxygen precovered surf ace and by adsorption of oxygen on the hot surface. For exposures up t o 10 L and temperatures up to 470 K a considerable part of the oxygen exists still in the chemisorbed state, another part transforms into Al oxide. In contrast to 300 K chemisorbed O-ad atoms are mobile at elev ated temperatures, and compact, hexagonal (1 X 1)O-ad islands develop by an ordinary nucleation and growth scheme, This evidences attractive interactions between the oxygen atoms on (1 X 1) sites, From the late ral distribution of O-ad islands a diffusion barrier of 1.0-1.1 eV is derived, The imaging of the islands of the (1 X 1) phase by STM depend s on their size, which is understood by a different imaging of the O-a d/Al adsorbate complexes at the island borders. Defects in the islands and bright features at the edges are interpreted as nuclei of aluminu m oxide. Additional features which appear as topographic holes may be attributed to nonconducting Al oxide grains. (C) 1998 American Institu te of Physics. [S0021-9606(98)01204-5].