Structure Determination of Inhomogenous Samples

Abstract

AES and XPS give surface analyses with a probe depth of a few atomic layers. As a direct consequence of this degree of surface sensitivity, many sample taken from the ordinary laboratory or industrial environment and analyzed in an electron spectrometer will be found to have a surface composition consisting of primarily carbon and oxygen. This is due to the inevitable presence of adsorbed hydrocarbons, water vapour, oxide layers, fingerprints and so on to be found on any surface that has been exposed to air, or handled without any special precautions being taken to maintain its cleanliness. Analysis of these unwanted contamination layers may on occasions be interesting in its own right but generally is not very useful. To overcome these problems requires a controlled method of removal of the adsorbed material in such a way that these surface contamination layers are carefully stripped away, exposing the material of interest below. Further, samples are frequently not homogeneous in composition with depth — indeed, if they were there would be no need for surface, as opposed to bulk, analysis — and a means of determining this compositional variation with depth is required for the analysis of practical samples. These requirements are met by the technique of ion beam depth profiling.