ENERGY DEPENDENT ION SCATTERING SPECTROSCOPY: A CHEMOMETRIC STUDY OF ITS ANALYTICAL UTILITY (PRINCIPAL COMPONENT, SELF MODELING)

The dependence of the backscattered ion yield intensity in Ion Scattering Spectroscopy (ISS) on the incident ion's energy is due to energy dependence of the differential scattering cross section and several ion neutralization pathways. In addition to the expected monotonic energy dependence, oscillations were also exhibited in the backscattered ion yields for noble gas ions scattering off certain elements. These oscillations seemed to be very sensitive to the chemical environment of the scattering atom and as such held some promise for extending the analytical information obtainable from the ISS technique. This work demonstrates the application of powerful data analysis tools from the area of chemometrics, such as principal component analysis and pattern recognition, in order to provide analytically useful interpretation of the energy dependent ISS spectra. A commercially available ISS instrument was modified and software developed to allow for computer control and automatic data acquisition in order to produce the oscillatory ion scattering spectroscopy (OISS) spectrum. The additional information contained in the energy dependence of the backscattered ion yield can improve the ability of ISS to identify the chemical components present on the sample surface, especially in case where conventional ISS may not have sufficient resolution to differentiate similar compounds. The analysis of mixtures and the preliminary work with adsorbed oxygen on a clean lead surface indicate that the technique of OISS may provide a good probe of surface coverage.