Oxidation of Pt(1Â 1Â 1) by gas-phase oxygen atoms

Increasing the atomic oxygen coverage above approximately 0.75 ML is shown to result in the growth of Pt oxide particles and disordering of the Pt surface. Decomposition of the Pt oxide particles produces explosive desorption of O2 that is characterized by a shift of the desorption peak to higher temperature and a dramatic increase in the maximum desorption rate with increasing oxygen coverage. The main characteristics of the explosive desorption are well reproduced by a kinetic model in which oxygen atoms are assumed to migrate from oxide domains onto regions of the surface containing chemisorbed oxygen atoms, and with oxygen atoms desorbing only from the chemisorbed layer. The implication of this mechanism is that Pt oxide is more thermodynamically favorable than high concentrations of chemisorbed oxygen atoms on Pt(1 1 1), and hence that the growth of Pt oxide on Pt(1 1 1) is kinetically limited.