Site-specific adsorption and diffusion of atomic H on the (111)-(7 x 7) surface at high temperatures were studied by means of scanning tunnelling microscopy. The H atoms were found to adsorb preferentially on rest-atom sites, rather than adatom sites with a binding-energy difference of about 0.2eV. The adsorption caused reverse charge transfer from rest-atoms back to adatoms. At above about 280C, atomic hopping between 2 rest-atom sites within a half-cell could occur and was mediated by an adatom site. At above about 330C, the H atoms started to hop across the cell boundary via 2 adatom sites, or diffused across the surface. The activation barrier to hopping from a rest-atom site to a corner adatom site was about 0.05eV lower than that to an edge adatom site. Thus, during cross-boundary jumps, they hopped preferentially via 2 corner adatom sites. The hopping barriers within the cell and across the cell boundary were determined from Arrhenius plots. The hopping paths, relative binding energies and site-selectivity of H atoms on the above surface agreed in general with theoretical results, but the present results were both site- and path-specific.

Diffusion by Bond Hopping of Hydrogen Atoms on the Si(111)-7 x 7 Surface R.L.Lo, M.S.Ho, I.S.Hwang, T.T.Tsong: Physical Review B, 1998, 58[15], 9867-75