Practical guides for x-ray photoelectron spectroscopy: Quantitative XPS

X-ray photoelectron spectroscopy (XPS) is widely used to identify chemical species at a surface through the observation of peak positions and peak shapes. It is less widely recognized that intensities in XPS spectra can also be used to obtain information on the chemical composition of the surface of the sample and the depth distribution of chemical species. Transforming XPS data into meaningful information on the concentration and distribution of chemical species is the topic of this article. In principle, the process is straightforward, but there are a number of pitfalls that must be avoided to ensure that the information is representative and as accurate as possible. This paper sets out the things that should be considered to obtain reliable, meaningful, and useful information from quantitative XPS. This includes the necessity for reference data, instrument performance checks, and a consistent and methodical method for the separation of inelastic background from peaks. The paper contains relevant and simple equations along with guidance on their use, validity, and assumptions.