X-RAY PHOTOELECTRON DIFFRACTION OF NIO - EXPERIMENTS AND CALCULATIONS IN AN EXTENDED SINGLE-SCATTERING-CLUSTER MODEL

We present a set of polar-angle-dependent x-ray photoelectron spectroscopy (XPS) measurements obtained from single-crystalline NiO, in situ cleaved and ion bombarded. The intensities of the O 1s and Ni 2p XPS peaks show characteristic x-ray photoelectron diffraction effects with intensity maxima in the low-index directions (e.g., [001], [101], [102], and [103]). The relative height of the maxima can partly be deduced from crystal geometry and scattering strength of O and Ni (derived from the atomic scattering factors), where O is a much weaker scatterer than Ni. Nevertheless it turns out that O plays an important role as a scatterer in these experiments, especially considering the O 1s emission along [101]. Experimental observations are compared to calculations for an improved single-scattering-cluster (SSC) model including a simulation of multiple scattering. This addition turned out to be necessary in order to get reasonable agreement of experiment and calculation while still retaining most of the ease and clarity of the original SSC model.