SURFACE-ANALYSIS OF WIDE-GAP INSULATORS WITH XPS

The positive surface charge induced by the photoelectron emission is a major problem in the XPS study of insulating materials. This paper is devoted to the definition of an XPS experimental procedure for the analysis of large gap oxides, three of which are considered: sapphire, quartz and yttria-doped-zirconia, their gap widths being respectively about 8.5, 9 and 5.5 eV. The influence of the substrate temperature on the charge is first described. The charge compensation is then studied using low energy electron bombardment (flood gun), which was calibrated prior to the experiments; the reliability and reproducibility of the XPS results (peak energy positions, FWHM and intensity) are discussed. The question of the Fermi edge and energy referencing for insulating materials, as well as the role of the surface potential on the neutralization conditions and its possible use in the analysis of insulating material are outlined. The last section establishes a set of technical recommendations for the analysis of insulators, pointing out the criteria to be chosen for optimizing the flood gun settings.