Chemical effects in ion scattering spectroscopy

Abstract

The principal use of low-energy ion scattering spectroscopy (ISS) as a surface analytical tool has been the identification of surface layer atoms through binary collision kinematics. In this mode of analysis, the chemical state of the atom is usually not discernible with the data normally obtained. This paper reviews a number of observations which indicate that chemical state information or the nature of local atom arrangements may be inferred from certain aspects of the experimental data. The earliest recognition of chemical state information resulted from study of resonant charge exchange processes for particular ion/atom combinations. By appropriate manipulation of experimental data, it is possible to obtain fingerprint spectra in the inverse velocity domain for various compounds. Recently, two techniques used in this laboratory have been applied to the study of surface atom configurations. In the first, the energy dependence of scatter peak height ratios in ionic compounds is used to infer an atom shielding susceptibility for various cations in oxide matrices. Secondly, a number of peak shift and doublet scattering peaks have been observed in special cases where the surface layer decomposes under bombardment by the probe ion beam.