INFRARED REFLECTION ABSORPTION-SPECTROSCOPY STUDY OF CHEMISORPTION ON THE NI(001)-C(2X2)SI SURFACE

Infrared reflection-absorption spectroscopy has been used to study the oxidation chemistry of Si atoms adsorbed on Ni(001) in a c(2 x 2) structure. Water (H2O, D2O) and oxygen ((O2)-O-16, (O2)-O-18) were used as the oxidizing species and the effects of variation in Si coverage (from the c(2 x 2) value of 0.5 monolayers) and of annealing, following adsorption near 300 K, were investigated. H2O adsorbs dissociatively, giving Si-OH stretching and Si-O-H bending modes at 1015 and 800 cm-1, respectively. There are, however, no detectable Si-H vibrations for exposure either to H2O or to H2 excited by a hot filament. The Si-OH stretch lies about 230 cm-1 higher in energy on c(2 x 2)Si than on elemental Si, indicating a substantial influence of the metallic environment on the Si-OH bond. O2 exposure leads to two types of bridging species - one giving bands at about 1090 and 830 cm-1 and another giving a band at about 990 cm-1. Based in part on the correlation between Si coverage and band relative intensities, these are assigned to Si-O-Si and Si-O-Ni bridges, respectively. Annealing leads to structural rearrangement of the surface layers, ultimately giving a spectrum resembling that for a thin SiO2 film on a metal.