H-enhanced mobility and defect formation at surfaces: H on Be(0001)

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Abstract
First-principles calculations of the interaction of H with the close-packed Be(0001) surface reveal that adsorbed H reduces barriers and formation 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 formation energy of steps, adatoms, and vacancies on Be(0001). Because H adatoms repel each other on the flat surface, but not if adsorbed at the defects studied here, the formation of these defects is especially facile 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.