We measured the diffusion coefficients for hydrogen (H) and deuterium (D) on Ni(111) from 108 to 154 K. We observed nonactivated tunneling following thermally activated hopping at around 125 K for both isotopes. The nonactivated tunneling rates show weak isotope dependence. Our observation confirms an early report by Lin and Gomer [Surf. Sci. 225, 41 (1991)]. The nonactivated tunneling is analyzed with both a modified polaron model, which includes adatom-phonon couplings varying quadratically in phonon coordinates, and the conduction electron model. The weak isotope dependence is understood as a result of a large WKB tunneling matrix element on Ni(111).
ASJC Scopus subject areas
- Condensed Matter Physics