Fluorine atom abstraction by Si(100) II. Model

A model is developed to describe the kinetics of the three scattering channels-unreactive scattering and dissociative chemisorption via single atom abstraction and two atom adsorption-that are present in the interaction of F-2 with Si(100). The model provides a good description of the non-Langmuirian coverage dependence of the probabilities of single atom abstraction and two atom adsorption, yielding insight into the dynamics of the gas-surface interaction. The statistical model is based on the premise that the two dissociative chemisorption channels share a common initial step, F atom abstraction. The subsequent interaction, if any, of the complementary F atom with the surface determines if the overall result is single atom abstraction or two atom adsorption. The results are consistent with the orientation of the incident F-2 molecular axis with respect to the surface affecting the probability of single atom abstraction relative to two atom adsorption. A perpendicular approach favors single atom abstraction because the complementary F atom cannot interact with the surface, whereas a parallel approach allows the F atom to interact with the surface and adsorb. The fate of the complementary F atom is dependent on the occupancy of the site with which it interacts. The model distinguishes between four types of dangling bond sites on the Si(100)(2x1) surface, based on the occupancy of the site itself and that of the complementary Si atom in the Si surface dimer. The results show that the unoccupied dangling bond sites on half-filled dimers are about twice as reactive as those on empty dimers, which is consistent with an enhanced reactivity due to a loss of a stabilizing pi interaction between the two unoccupied dangling bonds on a dimer. (C) 2000 American Institute of Physics. [S0021-9606(00)70811-7].