Introduction to x-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) has become one of the most widely used surface analysis techniques, and XPS instrumentation has become more user friendly, making the technique available to a large number of researchers. The number of experts in the field, however, has not increased, and XPS data are often misinterpreted in the literature. This paper is intended to provide an introduction to XPS for prospective or novice users. We present the basic principles of the technique including (1) the photoelectric effect, (2) how electrons interact with matter and escape from a surface and how this determines the surface sensitivity of the technique, and (3) how the chemical environment around an element affects the binding energy of its electrons. A description of the instrumentation helps a novice user understand how data are acquired, and information is included on sample preparation and mounting. The important parameters for data acquisition are noted to help guide users starting to acquire data. Interpretation of data on both a qualitative and quantitative level is discussed, and additional sections provide information on more advanced techniques such as angle resolved XPS, small area analysis, near ambient pressure XPS, valence XPS, and ultraviolet photoelectron spectroscopy.