Computer simulation of angle-resolved x-ray photoelectron spectroscopy measurements for the study of surface and interface roughnesses

Abstract

The development of nanoscale materials is always closely connected with their characterization. One powerful method of nondestructive analysis in the nanometer-depth region is angle-resolved x-ray photoelectron spectroscopy (ARXPS). The interpretation of such ARXPS measurements, however, needs model calculations based on a priori assumptions of the (typically unknown) surface structure under investigation. For rough surfaces, there often can be uncertainties, misinterpretations, and/or artifacts. In this paper a calculation method is presented which allows ARXPS intensities to be simulated conveniently and rapidly for almost any sample structure. The presented algorithms can be easily extended to include other physical effects (e.g., elastic scattering) and can also be used for other problems where spatial resolution for the description of absorption processes is needed. Illustrative calculations for selected surface structures (overlayers on rough substrates, island formation, and clusters) demonstrate how these simulations can help to estimate the limits of ARXPS analyses. Some previous findings (e.g., the “magic angle” for overlayers on rough surfaces) are critically examined. For more complicated small structures (islands and clusters), a complex interplay of various parameters must be considered. For small islands, edge and shadowing effects result in a general overestimation of the surface coverage, and near-surface clusters are often interpreted as artificially mixed layers of the materials.