Electron Mean Free Path, Attenuation and Escape Depth

2 Electron Mean Free Path, Attenuation and Escape Depth 

The variation of the mean free path with electron energy E can be described by an equation that has the form 

In XPS a method of determining the attenuation length is to use the overlayer method. The variation of the intensity of a species is determined as a function of the thickness of the overlayer. If the substrate is a silicon wafer and the overlayer has a thickness d, then the intensity of the silicon signal will be 7s, which according to eqn (9.39) is given by 

Element Core level Kinetic energy (eV) Mg K Xk (nm) Kinetic energy (eV) Al Ka Xk (nm) 

In the context of surfaces it is interesting to note that changing from Mg to A1 almost doubles the escape depth and hence allows the distribution of elements to be studied deeper into the surface. 

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