The adsorption, diffusion and ordering of H on Pd(111) was studied by scanning tunnelling microscopy at 37 to 90K. At low coverages, isolated H atoms were observed. They formed √3 x √3-1H islands as the coverage increased. Above 1/3ML, coverage areas of a new phase with a √3 x √3-2H structure were formed; with both structures coexisting between 1/3 and 2/3ML. Finally a 1x1 structure was formed after high exposures of H above 50K, with a coverage close to 1ML. Atomically resolved images revealed that H binds to face-centered cubic hollow sites.

Hydrogen Adsorption and Diffusion on Pd(111). T.Mitsui, M.K.Rose, E.Fomin, D.F.Ogletree, M.Salmeron: Surface Science, 2003, 540[1], 5-11