Hydrogen sorption sites in holmium silicide on silicon(1 1 1)

The hydrogen sorption sites on the surface of holmium silicide grown on Si(1 1 1) have been determined using metastable de-excitation spectroscopy, ultraviolet photoemission spectroscopy and density functional theory calculations. Comparison of calculated and measured surface density of states spectra allow us to locate the position of the second subsurface hydrogen atom in each unit cell to an interstitial site in the layer of rare earth atoms. The hydrogenation energies indicate a reaction pathway that involves concomitant site occupation.