Reactive scattering of halogen molecules from 〈111〉 surfaces of silicon and germanium: Comparison with oxygenic species

Abstract

The values of the reaction probabilities of Cl 2, Br 2 and I 2 were determined to be 0.3–0.5 independent of surface temperature at low gas pressures and surface temperatures above about 900 and 1100 °K for single-crystal surfaces of germanium and silicon, respectively. These values were the same magnitude as those for O and O 3 and were at least an order of magnitude higher than the reaction probability of molecular oxygen. The differences in reactivity of O, O 2, O 3 and the halogens was interpreted in terms of virtual dangling surface bonds which account qualitatively for the chemical interaction between the gas and solid during collision. In these terms the reactivity of molecular oxygen was low due to the severe steric requirement imposed by the necessity for interaction with adjacent surface orbitals to effect chemisorption. Atomic oxygen and the halogens were easily chemisorbed on a single site. Ozone interacted through its terminal oxygens with adjacent surface orbitals to produce dissociation.