T. Kammler et al., INTERACTION OF THERMAL H-ATOMS WITH NI(100)-H SURFACES - THROUGH SURFACE PENETRATION AND ADSORBED HYDROGEN ABSTRACTION, Surface science, 339(1-2), 1995, pp. 125-134
Considerable quantities, > 3 monolayers, of hydrogen (deuterium) were
absorbed in subsurface sites at Ni(100) surfaces via impact of thermal
H (D) atoms. Competitive to a direct transition (penetration) into th
e bulk with an initial probability of 4.5 X 10(-2) impinging H (D) ato
ms abstract adsorbed D (H) with an initial abstraction probability R =
0.25 and cross section of 1.6 Angstrom(2). The filling of subsurface
sites obeys a Langmuir-type rate law. An adsorbed H (D) monolayer does
not affect the probability for penetration into the bulk. Above 150 K
subsurface H (D) move to the surface and either recombine with adsorb
ed H (D) followed by recombinative desorption or get adsorbed at the s
urface if they encounter an empty site. The desorption kinetics from s
ubsurface sites is in quantitative agreement with thermodynamic bulk N
i/H data. Isotope effects were neither observed for bulk penetration n
or for abstraction.