Analyzing method of surface structures by X-ray photoelectron spectroscopy (XPS)

The single-scattering-cluster model for the simulation of X-ray photoelectron diffraction (XPD) of a GaAs(100)-c(8x2) surface has been investigated to obtain good agreement with the experimental XPD pattern. In the simulation by the single-scattering cluster-model with a spherical wave (SSC-SW), the calculation of the polar-scan XPD pattern is appreciably influenced by the cluster size as well as by the cluster shape and the agreement between the calculated and measured XPD patterns is not so good even for the very large cluster including 10(5) scatterer atoms. To overcome such influence and disagreement, it is important that the spatial distribution of the scatterer atoms is determined in terms of the scattering intensity of each scatterer atom: the only scatterer atoms with the scattering intensity above a specific critical vale epsilon should be taken into the simulation and all smaller scattering intensities than epsilon are cut down. The smaller critical value corresponds to the calculation with the scatterer atoms located at a deeper and wider position in the bulk. By choosing the critical value appropriately, the simulation obtained by the SSC-SW resembles well the measured Ga3d and As3d XPD patterns. The SSC model with a plane wave is also examined and compared with the SSC-SW model.