MAGIC-ANGLE FOR SURFACE-ROUGHNESS FOR INTENSITY RATIOS IN AES/XPS

The influence of surface roughness on total as well as angle-dependent signal electron intensities has been studied by means of an effective and simple theoretical model. It was found that the influence of surface roughness may be accounted for in the usual formalism for AES/XPS by using an effective depth distribution function (DDF). Comparison of the model with experimental results and Monte Carlo calculations are very satisfactory and indicate that the model developed here should provide useful guidance for quantifying the influence of surface roughness in XPS/AES. For an emission angle of similar to 35 degrees, the depth distribution function assumes an exponential form with an effective attenuation length varying only by a few per cent as the relative surface area, which characterizes the roughness, is varied over a large range. This result implies that the influence of surface roughness on a given intensity ratio is very small for this geometry and may usually be neglected. This statement not only pertains to a layered sample but applies to a specimen with an arbitrary depth profile. Generally, the effective DDF is dominated by the influence of surface roughness, while the effects of elastic scattering are less pronounced. In this case, the combined influence of surface roughness and elastic scattering is simpler to describe than the influence of elastic scattering on the signal electron emission process from an ideally flat sample.