An analytical Si/H potential was developed and was fitted to the results of first-principles electronic-structure calculations of H adatom adsorption and diffusion on embedded Si clusters. The latter were intended to model (100) 2 x 1. On the basis of this interaction potential, the rate constants were calculated for a H adatom that hopped from one site to another, parallel or perpendicular to the Si dimer rows. Monte Carlo simulations were used to extract exact classical transition-state theory rate constants. The diffusion constants for H adatoms which moved parallel to, or perpendicular to, the surface dimer rows were both found to exhibit an Arrhenius temperature dependence at temperatures ranging from 700 to 900K; with pre-exponential factors and activation energies of 4.0cm2/s and 38.1kcal/mol (parallel to dimer rows) or 0.48cm2/s and 62.8kcal/mol (perpendicular to dimer rows). The results confirmed a previous suggestion that anisotropic diffusion of H adatoms on the (100) 2 x 1 surface would occur preferentially along the edges of Si dimer rows. However, these predicted H adatom diffusion rates were orders of magnitude higher (along the dimer rows) or lower (across the dimer rows) than the measured rates of H2 desorption from (100) 2 x 1-H. It was concluded that H atoms might not be involved in the rate-limiting step for H desorption from Si(100).

First-Principles-Derived Rate Constants for H Adatom Surface Diffusion on Si(100)-2×1. C.J.Wu, I.V.Ionova, E.A.Carter: Physical Review B, 1994, 49[19], 13488-500