First-principles derived Monte Carlo simulations were made of H adatom diffusion on the Si(100)-2x1 surface. An analytical Si/H potential was developed which was fitted to the results of first-principles electronic structure calculations of H adatom adsorption and diffusion on embedded silicon clusters designed to model Si(100)-2x1. With this interaction potential, the rate constants were calculated for a H adatom hopping from one site to another, both parallel and perpendicular to the silicon dimer rows, using Monte Carlo simulations to extract exact classical transition-state-theory rate constants. The diffusion constants for H adatoms moving parallel and perpendicular to the surface dimer rows were both found to obey an Arrhenius temperature dependence (700 to 900K) with pre-exponential factors and activation energies of 4.0 x 100cm2/s, 38.1kcal/mol, and 4.8 x 10-1cm2/s, 62.8kcal/mol, respectively. These results confirmed the previous suggestion that anisotropic diffusion of H adatoms on the Si(100)-2x1 surface would occur preferentially along the edges of silicon dimer rows. These predicted H adatom diffusion rates were however, orders of magnitude faster (along the dimer rows) or slower (across the dimer rows) than measured values for the rates of H2 desorption from Si(100)-2x1-H. The results suggested that diffusion of hydrogen atoms might not be involved in the rate-limiting step for hydrogen desorption from Si(100).

First-Principles-Derived Rate Constants for H Adatom Surface Diffusion on Si(100)-2x1. C.J.Wu, I.V.Ionova, E.A.Carter: Physical Review B, 1994, 49[19], 13488-500