O-2 INTERACTION WITH PT(100)-HEX-R0.7-DEGREES - SCATTERING, STICKING AND SATURATING

The interaction of oxygen with the Pt{100}-hex-R0.7-degrees surface has been studied using supersonic molecular beams at incident translational energies from 0.06 to 0.9 eV and surface temperatures from 300 to 600 K. Scattering measurements show the existence of both intrinsic and extrinsic precursor states, and the trapping probability into these states is high at low incident energies. However, sticking probability measurements on the clean surface indicate that O2 dissociative adsorption on Pt{100}-hex-R0.7-degrees is a direct activated process, in contrast to that on Pt{100}-(1 X 1) or Pt{111}. Strong temperature enhancement of the initial sticking probability has been observed and accounted for partly by a dynamical barrier model. The sticking probability varies strongly with oxygen coverage, which is explained through computer simulations of island formation. The formation of small islands is demonstrated by TEAS measurements. Thermal desorption measurements show that, at high incident energies above 0.5 eV, new states are populated and higher coverages, up to a full monolayer, are reached.