2009 Volume 15 Issue 3 Pages 291-294
Angle resolved XPS is a useful method for obtaining non-destructive quantification of thin (4-6nm) layers with good absolute depth resolution. Although acquisition of ARXPS data with modern instrumentation is easy, determining the depth distribution of elements from the data is more challenging. The maximum entropy method (MEM) is a technique frequently used for solving the inversion problem in angle resolved XPS experiments. The necessary condition for the consistency of experimentally measured data with the MEM model (successful fit) is that the Laplace transform of the compositional depth profile (LTCDP) calculated from the experimentally measured normalised intensity is a monotonically decreasing function for all measured elements. We have found an efficient algorithm which can estimate the LTCDP for elements with attenuation lengths and provide an independent test of the suitability of the layered model for different sample elements. The practical application of this method is illustrated on analysis of a number of samples and conclusions on the use of these methods to generate elemental and chemical-state depth profiles are discussed.
