Modeling the interaction of hydrogen with silicon surfaces

We have investigated the prospects for developing model potentials for use in classical simulation of structural and dynamical properties of Si surfaces interacting with hydrogen. The point of view adopted requires that only short-range two-atom and three-atom interactions appear, and that these component functions should be fully transferable between small-molecule gas phase species (e.g. SiH and H2) and Si surfaces with arbitrary extent of hydrogenation. Using the silicon Stillinger-Weber potential as a starting point and guide, a moderately successful set of such interaction functions was derived by non-linear parameter optimization. This set displays proper bonding geometries and valence saturation when applied to several hydride species of intermediate molecular weight (e.g. Si4H10 and Si10H16), and to dimerized Si(100) in various stages of hydrogenation. Molecular dynamics simulations show relatively large sticking probabilities for impinging H atoms at low incident energies, whereas H2 at comparable energies experiences only non-sticking collisions, both roughly in agreement with experiment. Some shortcomings of the derived model have been identified, including deficient surface diffusion kinetics; however, possible improvement strategies have been identified.