Quantitative analysis of Auger lineshapes of oxidized iron

Abstract

A detailed data set of Fe(MNN) Auger lineshapes and O(511 eV)/Fe(LMM) Auger peak ratios for polycrystalline iron is reported as a function of oxygen exposure, and compared to corresponding X-ray photoelectron spectra. The data demonstrate that the Fe(MNN) lineshapes of Fe 3O 4 and Fe 2O 3 are extremely similar, and cannot be used to discriminate between these two oxides, except under nearly idealconditions. Other methods of determining iron oxidation states using relative heights of the Fe(LMM) peaks and O(KLL)/Fe(LMM) peak height ratios are critically evaluated. The data also demonstrate that although X-ray photoelectron spectroscopy is generally superior to Auger electron spectroscopy for determining iron oxidation states, the extreme surface sensitivity of the Fe(MNN) Auger peak provides certain advantages for analysis of the initial stages of iron oxidation. A methodology is discussed whereby this data set can be used to separate contributions to the O(511 eV) Auger peak due to iron oxides from contributions due to other oxides in multicomponent samples. In this manner, oxidation-state information can be obtained for individual components of multiple-element samples by Auger electron spectroscopy. In principle, this approach is applicable to transition-metal elements other than iron.