D abstraction by H on Si(1 1 1) surfaces

We studied H-induced abstraction (ABS) and adsorption-induced-desorption (AID) on the D/Si(1 1 1) surface for various initial D coverages θ0D and surface temperatures Ts. As θ0D was increased, the kinetics of HD ABS was found to switch from the first- to second-order rate law with respect to θD. D2 AID appeared to obey a nearly third-order rate law in θD. The hot atom mechanism was ruled out for both ABS and AID. We found that AID is associated with β2 temperature-programmed-desorption, i.e. D2 AID proceeds as a spontaneous desorption of deuterium from a di-deuteride or di-hydride phase formed by H atoms. Rate equations for HD and D2 desorptions at 620 K were proposed on the basis of the observed rate laws. The apparent activation energy of D2 AID was evaluated to be ∼0.16 eV for Ts⩽650 K. Taking steady state adsorption and desorption into consideration, the origin of the third-order rate law as well as the low activation energy for AID was ascribed to the process of sticking by H atoms rather than the process of D2 desorption. An isotope effect on both ABS and AID was recognized in the rate curve analysis. The hot complex-mediated reaction model was invoked to explain the complicated kinetic phenomena appeared in ABS and AID on the Si(1 1 1) surface.