X-Ray Photoelectron Spectroscopy (XPS) is a surface analysis technique used to determine the elemental composition and chemical state of materials. It involves irradiating a sample with X-rays and measuring the energy and number of emitted photoelectrons. XPS is a specialized skill that requires training and expertise in operating and interpreting spectral data from sophisticated equipment. Its applications include the study of surfaces in materials science, catalysis, electronics, and biomedical research.