Angle-resolved core-level spectroscopy of Zr1Nb alloy oxidation by oxygen, water and hydrogen peroxide

The initial oxidation of Zr1Nb alloy in oxygen, water and hydrogen peroxide at room temperature has been studied by angle-resolved x-ray photoelectron spectroscopy (ARXPS). The clean surface of alloy has been prepared either by scraping under ultrahigh (10(-10) mbar) vacuum or by argon ion sputtering. The four well-defined oxidation states of Zr were identified in the oxide films on Zr1Nb. The results of the ARXPS study were consistent with a layered structure of the oxide film, with zirconium dioxide in the outermost part of the film and suboxides in the inner region. The overall thickness of the incipient oxide layers ranged from 1.8 nm for the sputtered surface oxidized by oxygen, to 4.2 nm for the scraped surface oxidized in hydrogen peroxide. Mathematical analysis of the fitted Zr 3d spectra based on a layered structure model allowed us to estimate the thicknesses of individual suboxide layers. The population of suboxides as well as the binding energy of the Zr 3d electrons belonging to tetravalent zirconium were found to depend on the oxidizing agent and on the method used to clean the surface prior to oxidation. The amount of suboxides was much higher on the oxidized alloy surface cleaned by ion sputtering than on surfaces cleaned by scraping. The presence of zirconium hydride was observed in the spectra of Zr 3d electrons of the samples oxidized by water. The observed differences in binding energy of the Zr 3d component assigned to the Zr4+ oxidation state are interpreted by differences in the structure of the dioxide layer. Copyright (C) 2002 John Wiley Sons, Ltd.