DIFFUSION BY BOND HOPPING OF HYDROGEN-ATOMS ON THE SI(111)-7X7 SURFACE

Site-specific adsorption and diffusion of atomic hydrogen on the Si(11 1)-7X7 surface at elevated temperatures are studied by scanning tunnel ing microscopy. Hydrogen atoms are found to adsorb preferentially on r est-atom sites rather than adatom sites with a binding-energy differen ce of similar to 0.2 eV. The adsorption causes a reverse charge transf er from rest atoms back td adatoms. Above similar to 280 degrees C, at omic hopping between two rest-atom sites within a half-cell can occur which is mediated by an adatom site. Above similar to 330 degrees C, H atoms start to hop across the cell boundary via two adatom sites, or they can diffuse across the surface. The activation barrier for hoppin g from a rest-atom site to a corner adatom site is similar to 50 meV l ower than that to an edge adatom site. Thus, in cross boundary jumps, they hop preferentially via two corner adatom sites. From Arrhenius pl ots, the hopping barriers within the cell and across the cell boundary are determined. The hopping paths, relative binding energies, and sit e selectivity of hydrogen atoms on the Si(111)-7x7 surface agree in ge neral with theoretical results, but our result are both site and path specific. The dynamic behavior of two to three H atoms inside a half-c ell is also investigated. [S0163-1829(98)00939-4].