The adsorption and diffusion of single H atoms on Si(111)-7 x 7 surfaces at high temperatures were studied by using scanning tunnelling microscopy. It was noted that H atoms were preferentially adsorbed on top of rest atoms. An adsorbed H atom could hop, between 2 neighbouring rest atoms, via an adatom. That is, via a metastable intermediate state. At below 340C, the hopping was confined mainly within a half-cell. However, at higher temperatures, they could hop across the cell boundary. The activation energies for various hopping paths were measured. The binding energy differences between rest-atom and adatom sites, and between corner and edge adatom sites, were determined to be about 0.2eV and about 0.05eV, respectively.

Diffusion of Single Hydrogen Atoms on Si(111)-(7 x 7) Surfaces. R.L.Lo, I.S.Hwang, M.S.Ho, T.T.Tsong: Physical Review Letters, 1998, 80[25], 5584-7