Kinetics study on the hydrogen atom-induced abstraction and associative desorption of deuterium adatoms from the Si(100) surface at 573 K

Abstract

Hydrogen atom-induced deuterium adatom abstraction has been studied on the Si(100) surface from a desorption point of view. Abstraction of HD as well as collision-induced D2 desorption are observed on the D/Si(100) surface during H beam exposure at 573 K. For 1 ML Dad precoverage, about 30% of the desorbed D atoms are ejected as collision-induced D2 desorption at the very beginning of H(g) exposure. It is found that the decay of the HD and D2 rates are affected by the total coverage, θH+D. The decay rate of the HD rate is much lower in the low coverage regime than in the high coverage regime. The nominal cross section of the former is 2.3±1.0 Å2, while for the latter 7.2±0.5 Å2. The HD rate curves show that the abstraction obeys nearly first-order kinetics towards D coverage, θD. On the other hand, the D2 rate curves show that the collision-induced desorption obeys nearly fourth-order kinetics towards θD. Such HD abstraction is also observed on an oxygen-deposited D/Si(100) surface where the oxygen atoms are known to be incorporated between Si atoms. The observed decay rate of the HD rate is extremely low, with a cross section of 1.5±1.0 Å2. The reaction kinetics are well understood by adopting the kinetics model recently proposed by Flowers et al. [Surf. Sci. 396, 227 (1998)]. The abstraction of HD may be due to an Eley–Rideal mechanism rather than to a hot atom mechanism. Collision-induced D2 desorption may take place upon encounter of two dideuteride species via an isomerization reaction at quasiequilibrium.