Practical guide to the use of backgrounds in quantitative XPS

This guide is intended for both the novice in x-ray photoelectron spectroscopy (XPS) as well as users with some experience. XPS is one of the most widely used methods to characterize surface nanostructured samples, and XPS is now also commonly accessible to most material scientists through XPS facility centers. It is, therefore, increasingly used as a routine analysis technique to complement other techniques. This has led to an increase in the number of users who may not have a full understanding of the details of XPS and consequently must rely on the report provided by the XPS center. The purpose of this practical guide on the aspects of quantitative XPS is first to put the reader in a position to be able to understand and judge the meaning and possible errors in atomic concentrations based on analysis of peak intensities, which is the standard way quantitative XPS is reported. We discuss different ways to improve the analysis. This is attained by giving the reader a good understanding of how the intensities in the peak and the background of inelastically scattered electrons are linked together through the depth distribution of atoms. We then explore how this can be applied to greatly increase the capabilities of XPS to more accurately determine the composition and structure of surfaces on the nanoscale. This is possible at different levels of sophistication. We first see how a visual inspection of the XPS survey spectrum can be applied to get a quick rough indication of the structure. Next, we go through other more quantitative methods that are being used. The practical application of these techniques is illustrated by several examples.