X-ray excited aluminumK, copperLand zincLspectra from tarnished copper alloy surfaces

Abstract

Surface changes induced by atmospheric exposure of copper and copper-base alloys have been studied by X-ray excitation of AI K, Cu L, and Zn L X-ray spectra, using a conventional vacuum X-ray spectrograph. These are compared with spectral differences between pure metals and their oxides. The results are also related to published data obtained using electron excitation.Well defined 'chemical shifts' are observed in the AI K spectra from aluminum metal, AI203, and oxidized or tarnished aluminumcontaining alloys. Significant spectral differences are also seen between copper metal, its oxides, and tarnished copper-base alloys. As expected from elementary electron configuration data, the oxidation of zinc produces the smallest spectral change.The conclusion is that a conventional vacuum X-ray spectrograph provides sufficient resolution for the study of soft X-ray spectra in many practical applications involving surface reactions.Of the comtnen spectrographic techniques, soft X-ray spectroscopy appears the least extensively employed. Nevertheless, a recent review of the field (1) stated that: "For many years, X-ray spectroscopy has also been used to study the behaviour of electrons in solids. An analysis of X-ray emission and absorption spectra, due to transitions between a discrete inner atomic level of known characteristics and the various levels in the energy bands, usually provides the most straight-forward means of determining the distribution of the energy levels making up the band. These levels are weakly bound to the atom and describe the distribution of the occupied and unoccupied electron states in the s-olid. The physical and chemical states of an element thus modify its X-ray absorption edges and the neighbouring emission lines or bands, and information about the element's electronic orbitals in various chemical states can be obtained from X-ray spectra." Eric Niskanen is an Associate Research Engineer with the Department