Determination of substrate and overlayer intensity ratios for metal-metal systems in AES and XPS by a crystallographic electron attenuation model

A model has been presented which gives AES and XPS intensity ratios for metal/metal systems. Three interface constants, a substrate escape function, a substrate maximum-electronic-escape-depth and an overlayer maximum-electronic-escape-depth are introduced to characterize the interface. The normalized substrate and overlayer intensity ratios initially depend simple-exponentially on coverage, but from a certain coverage the dependence is not simple exponential. It is suggested, that this breaking point is not necessarily associated with the point of monolayer coverage, and a method to determine the monolayer position is given. No further breaking points are expected. The exponential decay constant is to good accuracy equal to the inverse overlayer attenuation length for coverages below one monolayer. It is shown, that the sum of normalized substrate and overlayer intensity ratios may be constant over a wide range of coverages.