H-Induced Reconstruction and Faceting of Al Surfaces

First principles calculations show that chemisorbed H causes vacancy reconstructions and faceting of all Al low index surfaces. On Al(111) H-decorated vacancies are stable; on H-covered Al(100) vacancies are easily activated thermally. H-covered Al(110) forms a missing row reconstruction with H-decorated vacancies on the $\{111\}$ microfacets. At high H coverages, low index Al surfaces are unstable against faceting. Al(111) and Al(110) form $\{211\}$ facets, on Al(100) islands and pits with $\{311\}$ and $\{211\}$ facets are stable. The H-induced structural changes are caused by the preferential binding of H at low coordinated Al surface atoms and at $\{100\}$ microfacets or, more generally, at “surface tetrahedral” sites.