Precursor molecular-oxygen state in the initial catalytic oxidation of the InP(110) surface modified by alkali metals

Abstract

The kinetics and the mechanism of the oxidation of the InP(110) surface modified by a cesium monolayer have been studied by valence-band and core-level photoemission spectroscopy using synchrotron radiation. The presence of a Cs monolayer on the InP(110) surface leads to an exceptional enhancement of the oxidation rate by 13 orders of magnitude with formation of phosphates such as ${\mathrm{InPO}}_{4}$. In strong contrast with cesiated transition-metal surfaces, we find a precursor state of molecular oxygen prior to the onset of InP(110) oxidation. At higher exposures, both molecular- and atomic-oxygen states coexist in a dynamic equilibrium.