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Concept
Photoemission spectroscopy
Summary
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 the substance. The term refers to various techniques, depending on whether the ionization energy is provided by X-ray, XUV or UV photons. Regardless of the incident photon beam, however, all photoelectron spectroscopy revolves around the general theme of surface analysis by measuring the ejected electrons.
X-ray photoelectron spectroscopy (XPS) was developed by Kai Siegbahn starting in 1957 and is used to study the energy levels of atomic core electrons, primarily in solids. Siegbahn referred to the technique as "electron spectroscopy for chemical analysis" (ESCA), since the core levels have small chemical shifts depending on the chemical environment of the atom that is ionized, allowing chemical structure to be determined. Siegbahn was awarded the Nobel Prize in 1981 for this work. XPS is sometimes referred to as PESIS (photoelectron spectroscopy for inner shells), whereas the lower-energy radiation of UV light is referred to as PESOS (outer shells) because it cannot excite core electrons.
Ultraviolet photoelectron spectroscopy (UPS) is used to study valence energy levels and chemical bonding, especially the bonding character of molecular orbitals. The method was developed originally for gas-phase molecules in 1961 by Feodor I. Vilesov and in 1962 by David W. Turner, and other early workers included David C. Frost, J. H. D. Eland and K. Kimura. Later, Richard Smalley modified the technique and used a UV laser to excite the sample, in order to measure the binding energy of electrons in gaseous molecular clusters.
Angle-resolved photoemission spectroscopy (ARPES) has become the most prevalent electron spectroscopy in condensed matter physics after recent advances in energy and momentum resolution, and widespread availability of synchrotron light sources.
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