Adsorbed states of H on Ni(111) at 100 K: A vibrational study

The adsorbed states of H on the Ni(111) surface have been investigated at 100 K as a function of H coverage, θH, mainly by using high-resolution electron-energy-loss-spectroscopy. Losses are observed at 90 and 130 meV for θH<~0.5. For θH=1, two losses are observed at 115 and 140 meV. In the region where 0.5<θH<1, vibrational spectra are the weighted superpositions of those for θH=0.5 and 1. We correlate losses for θH<~0.5 and 1 with the (2×2)-2H and (1×1)-H structures, respectively. No evidence of the quantum delocalization of H is obtained, which is attributed to the island formation of the (2×2)-2H structure even for the low θH.