Methodology for island surface structures investigation by x-ray photoelectron spectroscopy

Results of theoretical and experimental surface layers (thickness ranges of 0.1 - 1 angstroms) investigation via X-ray photoelectron spectroscopy (XPS) peak shape analysis are presented. XPS measurements of submonolayer gold coatings on silicon substrate were carried out on two installations: (1) SPECS installation with an energy analyzer capable of recording XPS spectra of photoelectrons emitted in the angular range from 27 to 75 degrees, and (2) KRATOS installation rotating the target to register XPS spectra at angles close to the normal and angles that are about 70 degrees with the normal. Calculations consistently showed a decrease in coating thicknesses with an increase in the viewing angle relative to the normal. The observed effect is described on the basis of a parallelogram island coverage model. This model made it possible to observe the change in the path length distribution function (PLDF) of the emitted photoelectrons depending on the viewing angle. PLDF determines the intensity ratio of the coating and the substrate XPS signals. Results obtained indicate that a series of experiments with angular resolution should be carried out to determine the average effective coating thickness. The value of the critical viewing angle, after which the thickness data are stabilized, is determined by the density distribution of the islands.