The chemical composition of the passive film on Fe24Cr and Fe24Cr11Mo studied by AES, XPS and SIMS

An analysis is made of published sputtering yield data for compounds using argon primary ions at normal incidence to evaluate the validity of simple predictive equations. These are sputtering yields at dynamical equilibrium. First, two archetypal compounds are analysed: GaAs with constituent elements of similar atomic number and weak preferential sputtering, and Ta2O5 with constituent elements of widely separate atomic number and strong preferential sputtering. The agreements of the sputtering yields predicted by the semi-empirical linear cascade theory are excellent when the appropriate parameters are interpolated, rather than using an average atomic number. The effect of preferential sputtering is included within the framework of the simple pair-bond theory. The average ratios of the data to the initial predictions for GaAs and Ta2O5 are 1.01 ± 0.06 and 1.00 ± 0.07, respectively. Extension of this analysis to a range of oxides shows that the heat of reaction of the oxidation process needs inclusion. It is here that the effect of preferential sputtering can lead to an expansion of the uncertainties. SiO2 is often used as a reference material and so the published yield data are analysed in detail. These show an extremely broad scatter and so new experimental data are measured. These new results are in the upper range of previous data and correlate with the semi-empirical theory with a scatter of only 9%. These correlations show that the semi-empirical linear cascade theory is excellent for predicting the energy dependence of the yield and can be excellent for absolute yields where the compound heat of formation is low.

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Sputtering yields of compounds using argon ions

Passive films formed on a Fe24Cr alloy in 0.5 M H2SO4 at 0.7 V are characterized by AES depth profiling and XPS. Obtained results and evaluation procedures are critically compared. It is found that correction for electron escape depth significantly improves the accuracy of AES profile data. The use of low energy peaks in AES allows metallic species to be distinguished from oxidized species and profiles with good depth resolution to be obtained. Quantification is impeded by peak overlap. XPS results depend significantly on the background subtraction and peak deconvolution procedure employed. From the different data it is concluded that the ratio Cr/Cr + Fe in the passive film studied is approximately 0.9 compared to 0.26 for the bulk alloy. The film thickness is 1.5 ± 0.3 nm. Within the precision of present XPS data the metal composition of the layers adjacent to the film is the same as that of the bulk.

Investigation of a passive film on an ironchromium alloy by AES and XPS

The composition and morphology of oxide films formed on type 304 stainless steel in lithiated high temperature water

Formation and diffusion properties of oxide films on metals and on nitride coatings studied with Auger electron spectroscopy and X-ray photoelectron spectroscopy

Auger electron spectroscopy (AES), in conjunction with argon ion sputtering, is frequently used to obtain composition versus depth profiles. Thin film thicknesses may be estimated from such profiles if the argon ion sputtering rate of a particular material is known. For this work, a series of oxide standards was prepared and calibrated with nuclear microanalysis techniques. These standards were then used to calibrate the composition versus depth profiles obtained using AES.

R. D. Davidson

Papers

Calibration of argon ion sputter rates using nuclear microanalysis and Auger spectroscopy