TEMPERATURE-PROGRAMMED DESORPTION STUDY OF THE ADSORPTION AND ABSORPTION OF HYDROGEN ON AND IN CU(111)

TPD studies of the interaction of atomic hydrogen with Cu(111) as a fu nction of coverage indicate the formation of chemisorbed and absorbed species at 98 K. At low coverage a single desorption feature, beta, is observed at 330 K. This desorption feature has been observed previous ly and assigned to desorption of chemisorbed surface species with a sa turation coverage of 0.5 ML. With increasing exposure, two more desorp tion features, alpha(1) and alpha(2), are observed at 200 and 220 K, r espectively. The alpha(1) state saturates quickly with a relative popu lation density of approximately 1/2 that of the beta peak. The alpha(2 ) state, however, did not saturate. At higher exposures, desorption fr om the alpha(2) state was greater than ten times the saturated beta st ate. The alpha(2) state exhibited zeroth order desorption kinetics wit h an activation energy for desorption of 8.8 kcal/mol and was attribut ed to desorption of an absorbed species from the bulk. (C) 1997 Elsevi er Science B.V.