The diffusion pathways of a silyl radical, adsorbed on the hydrogenated Si(100)-(2x1) surface, was studied by using density-functional theory. Preliminary searches for migration mechanisms were performed by using metadynamics simulations. Local minima and transition states were further refined by using the nudged-elastic-band method. Barriers for diffusion, from adsorption sites, as low as 0.2eV were found, but trap states were also spotted leading to a more stable configuration with escape barriers of 0.7eV. Diffusion among weakly bound physisorbed states was also possible with very low activation barriers (<50meV). However,desorption mechanisms (either as SiH3 or as SiH4) from physisorbed or more strongly bound adsorption configurations turned out to have activation energies similar to diffusion barriers. Kinetic Monte Carlo simulations based upon ab initio activation energies showed that the silyl radical diffused at most by a few lattice spacings before desorbing at 300 to 1000K.

Diffusion and Desorption of SiH3 on Hydrogenated H:Si(100)-(2x1) from First Principles. M.Ceriotti, M.Bernasconi: Physical Review B, 2007, 76[24], 245309 (12pp)