Inelastic peak shape method applied to quantitative surface analysis of inhomogeneous samples

Abstract

The validity of the peak shape analysis method for quantitative determination of the surface composition by electron spectroscopy is studied. To this end, inhomogeneous samples were produced by evaporating Ag and Au in varying amounts onto the (111) surface of a Ni single crystal. The amounts of deposits were monitored by a quartz crystal microbalance (QCM). The spectra from major x-ray excited core level peaks from the substrate and adsorbate were analyzed quantitatively using the ‘‘universal’’ inelastic scattering cross section. The data were analyzed by a three parameter model for the in-depth concentration profile corresponding to a layer-by-layer plus island (Stranski–Krastanov) growth model. By adjusting the three structural parameters, the intensity as well as the shape of all background corrected peaks from both substrate and adsorbate were found to fit exceptionally well with those of pure elemental samples. For both the Ag/Ni and the Au/Ni system, the total amount of evaporated material determined by the peak shape analysis method was found to be proportional to the observed QCM frequency shift to within ∼10% and the deviation is slightly larger for the highest amounts of evaporated adsorbate. Possible effects of elastic electron scattering are discussed.