Hydrogen-Adsorption-Induced Reconstruction of Tungsten (100): Observation of Surface Vibrational Modes

The surface vibrational modes of atomic hydrogen adsorbed on W (100), observed by electron-energy-loss spectroscopy in off-specular directions, indicate bridge bonding at all coverages. The vibrational frequencies show a dependence on the W-H-W bond angle which changes due to reconstruction of the tungsten lattice. The results indicate a W (100) $c[2\mathrm{}\times 2]\mathrm{H}$ low-coverage ${\beta }_2$ phase consisting of atoms occupying bridge sites on a $(\sqrt{2}\times \sqrt{2})R45\mathrm{}°$ reconstructed substrate similar to the clean crystal surface at low temperatures.