AES and EEL spectra from Zr, Zr + O 2 and ZrO 2; peak energy shifts and intensity variations at various stages of oxidation in the pressure range 10 −6−10 3 Torr

Abstract

Oxygen chemisorption and oxidation of polycrystalline Zr, up to 1 atm O 2 pressure, was followed by Auger electron spectroscopy and low resolution electron loss spectroscopy. A comparison of AES spectra from various oxidation states of Zr with spectra from bulk ZrO 2 gives useful information about the oxidation status of the surface. The intensity change and energy shifts, with oxygen exposure, are very different for different Zr AES peaks, as previously observed by Foord et al. [Surface Sci. 94 (1980) 339]. This behaviour is demonstrated quantitatively and discussed in relation to the different electronic origins of the various Auger transitions. The strong damping of Zr Auger peaks involving valence electrons cannot be merely attributed to peak broadening as recently proposed by Zhou et al. [Surface Sci. 139 (1984) L181], but is more likely due to change transfer from Zr to O. EEL spectra were found useful in explaining satellite structures from the strongest AES peaks. The oxidation kinetics, show that very large oxygen doses are required to completely saturate the surface region with oxygen. However, the outermost atomic layer(s) very quickly becomes oxide-like. At large exposures the amount of oxygen uptake, depends both on oxygen dose and on pressure, indicating that the O 2 dissociation rate or the transport of O atoms through the oxide film rather than the transport of Zr atoms becomes rate limiting.