Quantitative AES. V. Practical analysis of intensities with detailed examples of metals and their oxides

Abstract

A study is made of the metal and oxygen Auger electron intensities of a range of metals and their stoichiometric oxides from the high-resolution digital Auger electron database. The changes in peak shape for the oxygen Auger electrons is analysed and it is shown that, for a constant oxygen peak area, the direct spectrum peak heights and the differential peak-to-peak intensities each scatter over factors of 3 and 5, respectively. However, by broadening the spectra with a Gaussian function of up to 20 eV width, the scatters in the differential peak-to-peak heights can be reduced to a relative standard deviation of ∽5%. The broadening and differential method is not as accurate as a full analysis of peak area with all the necessary corrections, but it is simple and rapid and is about five times more accurate than existing simple differential procedures. The use of the broadened differential peak-to-peak intensities will need new sensitivity factors for quantification, which may be derived from traditional values and the data presented here. The relative intensities of the L2,3M2,3M2,3, L2,3M2,3M4,5, L2,3M4,5M4,5 metal peaks for Ti to Zn in the metallic and oxide states are also analysed and are shown to correlate well with theoretical predictions. However, small differences for the areas of these peaks between the metallic and oxide states are seen, leading to a relative standard deviation of 2.9% in the intensity ratios. These differences correlate with a simple model for the effect of oxygen on the effective number of valence electrons available in the metal M4,5 level contributing to the relevant Auger electron transitions. This results in a small change in the relative intensities of the metal peaks on oxidation. Measurements for the oxygen Auger electrons show a complementary effect. These results show that the relative area of a single intense peak in the multiplet structures for the metals and for oxygen varies by typically 2.9% and 6.7%, respectively, when normalized against the respective total peak areas. These uncertainties add to the overall uncertainties in quantifying data in AES analysis where a single peak in the group is used, e.g. in analysis using traditional differential spectra. © 1998 John Wiley & Sons, Ltd.