Photoelectron spectroscopy

Photoelectron spectroscopy also known as photoemission spectroscopy (PES) 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. 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 which is ionized, allowing chemical structure to be determined. Siegbahn was awarded the Nobel Prize in 1981 for this work. In the ultraviolet region, the method is usually referred to as photoelectron spectroscopy for the study of gases, and photoemission spectroscopy for solid surfaces. Ultra-violet 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 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. Extreme ultraviolet photoelectron spectroscopy (EUPS) lies in between XPS and UPS. It is typically used to assess the valence band structure.[4] Compared to XPS it gives better energy resolution, and compared to UPS the ejected electrons are faster, resulting in a better spectrum signal.

Further information 

1. Nordling, Carl; Sokolowski, Evelyn; Siegbahn, Kai (1957). "Precision Method for Obtaining Absolute Values of Atomic Binding Energies". Physical Review 105: 1676.
2.  Sokolowski E., Nordling C. and Siegbahn K., Ark. Fysik. 12, 301 (1957)
3.  Turner, D. W.; Jobory, M. I. Al (1962). "Determination of Ionization Potentials by Photoelectron Energy Measurement". The Journal of Chemical Physics 37: 3007.
4. Bauer, M.; Lei, C.; Read, K.; Tobey, R.; Gland, J.; Murnane, M.; Kapteyn, H. (2001). "Direct Observation of Surface Chemistry Using Ultrafast Soft-X-Ray Pulses". Physical Review Letters 87: 025501.
5. Физический энциклопедический словарь, М.: «Советская энциклопедия», 1984.
6. Article Photoemission spectroscopy from Wikipedia, the Free Enciclopedia. Available under the license Creative Commons Attribution-Share Alike.

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