X-ray photoelectron spectroscopy (XPS) is an analytical technique used to determine the elemental composition and chemical state of materials. It works by irradiating a sample with X-rays, which causes the emission of photoelectrons. By measuring the kinetic energy of these emitted electrons, researchers can identify the elements present and their chemical states. XPS is particularly useful in studying surfaces and thin films, as it provides information about the top few nanometers of a material. This technique is widely applied in fields such as materials science, chemistry, and nanotechnology for characterizing various substances, including metals, polymers, and semiconductors.