Computational Studies of Heterogeneous Reactions of SiH2 on Reconstructed Si(111)-(7x7) and Si(111)-(1x1) Surfaces.

摘要

The dynamics of chemisorption and decomposition of Cyclosilane on Silicon (111)-(1x1) and reconstructed Si(111)-(7x7) surfaces have been investigated using classical trajectories on a previously described potential-energy surface modified to yield the experimental bending frequencies for chemisorbed hydrogen atoms and to incorporate the results of ab initio calculations of the repulsive interaction between SiH2 and closed-shell lattice atoms. The Binnig et al. model is employed for the (7x7) reconstruction. The major mode of surface decomposition on the (7x7) surface is by direct molecular elimination of H2 into the gas phase. Hydrogen atom dissociation to adjacent lattice sites is a much slower process and the chemisorbed hydrogen atoms thus formed exhibit very short lifetimes on the order of (1.13-10.6)x10 888 to the -13th power. The rate coefficients for the decomposition modes are calculated. The rates on the (1x1) surface are faster due to the increased exothermicity released by the formation of two tetrahedral Si-Si bonds upon chemisorption compared to a single Si-Si bond on the (7x7) surfaces. Molecular beam deposition/decomposition experiments of Silane on Si(111)-(7x7) surfaces that chemisorbed hydrogen atoms are not formed in the SiH4 decomposition process whereas the present calculations suggest that such a reaction, although slow, does occur subsequent to SiH2 chemisorption. Reprints. (aw)