LAUSR

A simple analytical function is derived to describe the interface shapes measured in sputter depth profiling using XPS or SIMS. This function involves the convolution of a central Gaussian function, often taken to describe the roughness, together with an exponential tail to describe mixing and exponential approach often taken to be an information depth. This model is consistent with Hofmann's MRI model which does the same by numerical analysis but we present a direct analytical function which is more transparent to the user. The differential of the function gives Dowsett's function for delta layers. Depending on which of the three base functions are identified as sample related, the analyst can obtain the centroid of the underlying composition. These functions are used to show how the common measures of depth resolution for step edges and delta functions diverge as the profile becomes less Gaussian.