Interaction of hydrogen with the Ag(111) surface

The interaction of atomic hydrogen with the Ag(111) surface was studied with low-energy electron diffraction (LEED), high-resolution electron-energy-loss spectroscopy (HREELS), thermal desorption spectroscopy, and work function measurement. The adsorption of atomic hydrogen at 100 K induces a reconstruction of the Ag(111) surface, as indicated by an intense (2×2) (at 0.25–0.5 ML) and a mixture of (2×2) and (3×3) (at 0.5–0.6 ML) superstructures in LEED. The H-induced work function change (Δ${\mathrm{\Phi }}_{\max }$=+0.32 eV) is uncharacteristically large for the close-packed surface and indicative of the surface structural change. HREELS data show that H occupies a single site of high symmetry for all coverage. The observation of two vibrational modes (one dipole active at 106 meV and the other not dipole active at 87 meV at ∼0.5 ML) allows an assignment of bonding at a threefold hollow site. Both modes show measurable shifts in energy with increasing coverage, indicating an appreciable H-H lateral interaction. Atomic hydrogen adsorbed on Ag(111) recombines and desorbs at a temperature ∼180 K, appreciably lower than those for Cu and transition metals. The properties of H adsorption on Ag will be compared to Cu and to transition metals.