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A detailed electron spectroscopy for chemical analysis (ESCA) examination has been performed on a series of very pure rare earth foils, powders, and a sputter-deposited thin film consisting of yttria doped ceria. The foils were studied with their natural passivation layer intact and also sputter etched to provide approximate chemical profiles. The metals examined were cerium, lanthanum, and yttrium. The ESCA spectra of all of the passivated metals experienced charge shifts. Treatment of those shifts with an electron flood gun is an integral part of this study.
A semiquantitative analysis of the passivation layer of cerium establishes that the outer mantle is a mixed oxide-hydroxide Ce(IV) system, whereas the inner layers of the oxidative growth are initially mixed oxide-hydroxide Ce(III) systems and finally (close to the virgin metal) a substance believed to be Ce(III)2O3 is exposed. This is the first ESCA spectral analysis of the sesquioxide. Interestingly, sputter etching the ceric oxide/yttrium oxide (CeO2/Y2O3 film results in a nearly identical chemical development, indicating that some of these results may occur because of sputter reduction. The lanthanum and yttrium systems also display evidence of hydroxide formation on their outer (passivation) surfaces. A unique species which may be La(II)O is detected after sputtering into the passivation layer of lanthanum. The yttrium spectra for the CeO2/Y2O3 film exhibit superior resolution compared to that for the yttrium foil. A discussion of the satellite structure of these spectra is included.
quantitative analysis, materials, spectroscopy, rare earth alloys
Senior research chemist, UOP Incorporated, Des Plaines, Ill