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

Passive films formed on a Fe 24 Cr alloy in 0.5 M H 2 SO 4 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.