Diffusion of excessively adsorbed hydrogen atoms on hydrogen terminated Si(100)(2×1) surface

The diffusion properties of an excess H atom adsorbed on a fully H-terminated Si(100)(2 × 1)-H surface have been analyzed by means of density functional theory-generalized gradient approximation calculations. Our diffusion pathway models consist of sequences of hops between metastable Si surface atomic structures with an excess H atom. We analyzed the reaction path and corresponding barrier height in each hop using the climbing image nudged elastic band method. The activation energies for diffusion along intra-dimer, intra-row, and inter-row pathways are found to be 0.11, 0.54, and 0.74 eV, respectively, which are quite small compared to the common H diffusion running with a vacant site of hydrogen termination. The weak adsorption energy of the excess H atom is responsible for the small activation energy of diffusion. The present diffusion mechanism suggests that the physical substance of the “hot atom mechanism” proposed in the previous investigations on H exposure onto the Si surface is related to the metastable structures of excessively adsorbed hydrogen atoms.