Hydrogen-induced reconstruction of the W(100) surface,studied by surface core level spectroscopy

We report W(4?) surface core level shifts which yield new information on the energetics of the W(100) (1 × 1) → C(2 × 2)H phase transition. At small hydrogen coverages we find two co-existing surface core levels from atoms on normal lattice sites and from atoms in reconstructed domains. These surface levels are shifted to smaller binding energy (toward E_F) by 0.35 eV and 0.13 eV relative to the bulk level, respectively. The most stable configuration is obtained at a fractional coverage θ_H ? 0.2, at which all surface atoms are shown to be paired with neighboring atoms in the surface plane.