Effect of hydroxylation upon the ion scattering spectra of oxide surfaces

The low energy sputter peak is an artifact found in many ISS spectra at energies below those predicted for binary elastic backscattering. In this study, a correlation is shown between the intensity of the low energy sputter peak in 3He+ ion scattering spectra and the degree of hydroxylation of the surfaces of silicon and aluminium oxide. The spectra for the clean and hydroxylated surfaces of silica glass (SiO2) were examined. It was found that as the degree of hydroxylation increased, the sputter peak intensity increased and the amount of elastic scattering from surface atoms decreased due to atomic shielding by the chemisorbed hydroxyls. The spectra for materials hydroxylated in bulk (silica gel (SiO2.nH2O) and gibbsite (Al(OH)3)) were also analyzed and these further verified this interpretation of the sputter peak intensity. On the basis of these observations, the low energy sputter peak in ISS has been attributed to the detection of positively sputtered ions such as the hydrogen (H+) and matrix species (e.g. Si+, SiO+, and O+). These were detected in a separate experiment by secondary ion mass spectroscopy (SIMS). (author)