Rate equations for collision-induced desorption and abstraction in the reaction system H(g)+D/Si(100)-> D-2,HD at 573 K

Collision-induced desorption (CID) and Eley-Rideal (ER) type abstraction ha ve been investigated in the reaction system, H(g) + D-ad/Si(100)--> D-2,HD, at surface temperature of 573 K where dihydride phase is unstable. Rate eq uations for CID were obtained based on a second-order kinetics with respect to doubly occupied Si dimers DSi-SiD, DSi-SiH, and HSi-SiH, which are cons idered as parent species of transiently formed dihydrides, DSiD, DSiH, and HSiH, respectively. The coverages of the doubly occupied dimers were determ ined as a function of H exposure time by means of temperature-programmed-de sorption (TPD), and then the rate equations were calculated. As a result, t he experimental D-2 and HD rate curves were reasonably fit with the rate eq uations formulated. This fact indicates that CID is induced when two dihydr ide species encounter during their propagation via dihydride-monohydride is omerization reactions. It was found that HSi-SiH does not play a role in CI D of both D-2 and HD. Possible origins of this isotope effect were discusse d in terms of quantum effects on associative desorption and diffusion proce sses. The HD rate curve due to direct ER abstraction channel was fit with a first-order kinetics in D-ad coverage for a low coverage regime where dang ling bonds exist. However, for a high coverage regime where the surface is saturated, the HD rate curve was fit with DSi-SiD coverages, suggesting tha t D-ad that are paired up with H-ad in the same Si dimers are not abstracte d. (C) 2000 American Institute of Physics. [S0021-9606(00)72033-2].