High energy X-ray sources for photoelectron spectroscopy

• Main Author: West, Robin Henry
• Published: University of Surrey 1983
• Subjects: 669; Metallurgy & metallography
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.345915

X-Ray photoelectron spectroscopy (XPS or ESCA) is enhanced, as a surface analytical technique, by excitation with higher energy x-rays. Three characteristic x-rays , Si Ka (1739. 4eV), Zr La (2042. 4eV) and monochromatized Ag La (2984. 3eV) together with Bremsstrahlung were developed. Si Ka x-rays generate new XPS peaks from aluminium and bromine and although slightly broader than conventional XPS sources, benefits from weaker satellite peaks. Sensitivity factors of 110 subshells from 45 elements were measured and compared with theoretical photoionization cross sections, providing a close fit. Zr La x-rays are a valuable source for studying Al-Si compounds, with the generation of strong Al and Si, Is and KLL Auger peaks. The resultant Al and Si Auger parameters were studied for 30 silicates and comparison with refractive index data allowed the Auger parameters to be directly related to the polarization energy of the 0 ions surrounding Al and Si sites. The 0 polarizability dominates bulk polarizability in silicates and is highly variable around tetrahedral Si and Al sites, but almost invariant around octahedral Al. Consequently the surface coordination state of Al can be determined accurately. The Si KLV/KLL Auger intensity ratio measured the filling of the Si valence band during the Auger process and varied proportionally with the extra-atomic relaxation energy, as measured by the Si Auger parameter. Bremsstrahlung induced Auger peaks have been combined with photoelectron peaks in conventional XPS, to form an Auger parameter. These Si and Al Auger parameters from compounds and silicates were found equivalent to those obtained in Zr La XPS. Ag La x-rays were monochromatized by fitting an Ag anode to a conventional Al Ka monochromator. New XPS lines were generated, especially the Is and KLL Auger series from Al to Cl and benefitted from a reduced linewidth. Pretreated glass fibres were analysed and surface chemical state information extracted.