Nondestructive compositional depth profiling using variable-kinetic energy hard X-ray photoelectron spectroscopy and maximum entropy regularization

We discuss the calculation of nondestructive compositional depth profiles from regularization of variable kinetic energy hard X-ray photoelectron spectroscopy (VKE-XPS) data, adapting techniques developed for angle-resolved XPS. Simulated TiO2/Si film structures are analyzed to demonstrate the applicability of regularization techniques to the VKE-XPS data and to determine the optimum choice of regularization function and the number of data points. We find that using a maximum entropy-like method, when the initial model/prior thickness is similar to the simulated film thickness, provides the best results for cases where prior knowledge of the sample exists. For the simple structures analyzed, we find that only five kinetic energy spectra are necessary to provide a good fit to the data, although in general, the number of spectra will depend on the sample structure and noisiness of the data. The maximum entropy-like algorithm is then applied to two physical films of TiO2 deposited on Si. Results suggest interfacial intermixing. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.