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 0.250.5 ML) and a mixture of (2×2) and (3×3) (at 0.50.6 ML) superstructures in LEED. The H-induced work function change (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. © 1995 The American Physical Society.