Algorithm for automatic x-ray photoelectron spectroscopy data processing and x-ray photoelectron spectroscopy imaging

Abstract

It is well known that x-ray photoelectron spectroscopy (XPS) quantification based only on the measured XPS-peak intensity can lead to large errors. The problem, which is caused by the strong depth dependence of the intensity contribution due to inelastic electron scattering, was solved by developing algorithms for analysis of the energy distribution of emitted electrons. These algorithms are now widely used but since their practical application requires operator interaction, they are not well suited for automatic data processing. A simplified algorithm that is sufficiently robust (i.e., insensitive to variations in analysis procedure) to be suitable for automation was suggested recently [J. Vac. Sci. Technol. A21, 1081 (2003)]. For each XPS peak, this algorithm determines the total amount of the corresponding atoms within the outermost approximately three inelastic electron mean free paths and it also gives an estimate of their depth distribution. Since the algorithm can be automated, it should also prove useful in XPS imaging. In the present article, we investigate the applicability of the algorithm by analysis of nanometer thin Au films deposited on a Ni substrate. The XPS signals from both the overlayer Au 4d and the substrate Ni 2p peaks are analyzed and it is found that the analysis gives amounts of atoms that are in good agreement with nominal thicknesses determined by a more elaborate analysis as well as by Rutherford backscattering spectroscopy. Analysis of the substrate Ni 2p peak gives results that are in agreement with the results from analysis of the overlayer Au 4d peaks and the determined depth distributions of both elements are also in agreement with the known distributions.