Computer simulation of ARXPS at nanostructured surfaces

Motivation and results

The development of nano-scale materials is always closely connected with their characterization. One powerful method of non-destructive analysis in the nm-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. We developed a computer simulation method, which allows ARXPS intensities to be simulated conveniently and rapidly for almost any sample structure. This algorithm 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, 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, 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. The amount of material of the overlayer is systematically underestimated then.

Outlook

The simulation procedure will be extended by the influence of elastic scattering. We want to study the interplay of complex surface structures and measuring inaccuracies for ARXPS investigations.

References

S. Oswald, F. Oswald: Computer simulation of ARXPS measurements for the study of surface and interface roughness, J. Appl. Phys. 100 (2006) 104504-(1-9) (doi:10.1063/1.2386938).

S. Oswald, F. Oswald: Modeling of surface roughness for ARXPS, phys. status sol. (c) 4 [6] (2007) 1817–1821 (doi:10.1002/pssc.200675220).