Role of surface Al2O3 clusters on the kinetics of Al(111) oxidation

The effect of aluminum-oxide clusters on the Al(111) surface on subsequent oxygen adsorption at 300 K was investigated for both low and high degrees o f oxidation using x-ray photoelectron spectroscopy and high-resolution elec tron energy-loss spectroscopy. Oxide clusters on the Al(111) surface were p roduced by annealing chemisorbed O layers of various coverage up to 773 K. Only the chemisorbed oxygen phase was found to form at 243-300 K after addi tional O-2 exposure on surfaces containing both low- and high-oxide-cluster populations. The chemisorbed O adatoms produced were not influenced by the oxidic phase, exhibiting spectroscopic features similar to those observed upon chemisorption on the clean surface without oxide clusters. Oxygen adso rption on the surface with both low- and high-oxide-cluster populations pro ceeded with the same rate as found on the clean Al(111) surface. The observ ed effect is postulated to be due to an increase of the number of the vacan t Al adsorption sites liberated upon transformation of chemisorbed O adatom s into oxide clusters. (C) 2000 American Institute of Physics. [S0021-8979( 00)04511-4].