Quantitative analysis of a submonolayer adsorption system by angle resolved XPS: c(2×2)S on Ni(001)

Abstract

The polar and azimuthal angular dependences of core-level x-ray photoelectron peak intensities from c(2×2)S on Ni(001) are studied in detail in order to determine the accuracy of such measurements for quantitative analyses of such adsorbate/substrate systems. Comparison of Ni 2p3/2, Ni 3p, and S 2p intensities and various intensity ratios with a simple quantitative model for polar angle variations shows very good agreement in general, and suggests accuracies of ≲±20% in determining the fractional monolayer coverages of the adsorbate. Properly averaging over strong x-ray photoelectron diffraction effects in the single-crystal substrate is essential. Also, a correct allowance for Ni satellite intensities is found to be important. Finally, it is found to be adequate to assume that the overlayer is nonattenuating for emission angles ≳20° above the surface.