H-ENHANCED MOBILITY AND DEFECT FORMATION AT SURFACES - H ON BE(0001)

First-principles calculations of the interaction of H with the close-p acked Be(0001) surface reveal that adsorbed H reduces barriers and for mation energies for Be surface defects. A H atom adsorbed on top of a Be adatom reduces the Be atom's surface-diffusion barrier by a factor of 3. Preferential binding of H to surface defects reduces the formati on energy df steps, adatoms, and vacancies on Be(0001). Because H adat oms repel each other on the flat surface, but not if adsorbed at the d efects studied here, the formation of these defects is especially faci le at high H coverage. These results explain the experimental findings that the H-induced vacancy reconstructions, which dominate the high H coverage regime, form at as low as 100 K.