Photoemission spectroscopy (
PES), also known as
photoelectron spectroscopy, refers to energy measurement of electrons emitted from solids, gases or liquids by the
photoelectric effect, in order to determine the binding energies of electrons in a substance. The term refers to various techniques, depending on whether the
ionization energy is provided by an
X-ray photon, an
EUV photon, or an
ultraviolet photon. Regardless of the incident photon beam however, all photoelectron spectroscopy revolves around the general theme of surface analysis by measuring the ejected electrons.