Editing X-ray photoelectron spectroscopy (section)

==History==
[[File:Silver Target in XPS Spectrometer cropped.jpg|thumb|350x350px|An inside view of an old-type, non-monochromatic XPS system.|alt=]]
[[File:Example of an XPS tool.jpg|thumb|Example of an X-ray Photoelectron Spectrometer]]
In 1887, [[Heinrich Rudolf Hertz]] discovered but could not explain the [[photoelectric effect]], which was later explained in 1905 by [[Albert Einstein]] ([[Nobel Prize in Physics]] 1921). Two years after Einstein's publication, in 1907, P.D. Innes experimented with a [[Wilhelm Röntgen|Röntgen]] tube, [[Helmholtz coils]], a magnetic field hemisphere (an electron kinetic energy analyzer), and photographic plates, to record broad bands of emitted electrons as a function of velocity, in effect recording the first XPS spectrum. Other researchers, including [[Henry Moseley]], Rawlinson and Robinson, independently performed various experiments to sort out the details in the broad bands.{{citation needed|date=July 2019}} After [[World War II|WWII]], [[Kai Siegbahn]] and his research group in [[Uppsala]] ([[Sweden]]) developed several significant improvements in the equipment, and in 1954 recorded the first high-energy-resolution XPS spectrum of cleaved [[sodium chloride]] (NaCl), revealing the potential of XPS.<ref>{{cite journal|doi= 10.1016/S0029-5582(56)80022-9|title=β-Ray spectroscopy in the precision range of 1 : 10<sup>5</sup>| year=1956|last1=Siegbahn|first1=K.|last2=Edvarson|first2=K. I. Al|journal=Nuclear Physics|volume=1|pages=137–159|issue= 8|bibcode = 1956NucPh...1..137S }}</ref> A few years later in 1967, Siegbahn published a comprehensive study of XPS, bringing instant recognition of the utility of XPS and also the first [[Hard x-ray|hard X-ray]] photoemission experiments, which he referred to as Electron Spectroscopy for Chemical Analysis (ESCA).<ref>{{Cite book |first=Kai |last=Siegbahn |url=http://worldcat.org/oclc/310539900 |title=ESCA atomic, molecular and solid state structure studies by means of electron spectroscopy : Presented to the Royal Society of S#ience of Uppsala, Dec. 3rd, 1965 |date=1967 |publisher=Almqvist & Wiksell |oclc=310539900}}</ref> In cooperation with Siegbahn, a small group of engineers (Mike Kelly, Charles Bryson, Lavier Faye, Robert Chaney) at [[Hewlett-Packard]] in the US, produced the first commercial monochromatic XPS instrument in 1969. Siegbahn received the [[Nobel Prize]] for Physics in 1981, to acknowledge his extensive efforts to develop XPS into a useful analytical tool.<ref>[http://nobelprize.org/nobel_prizes/physics/laureates/1981/siegbahn-lecture.html Electron Spectroscopy for Atoms, Molecules and Condensed Matter], Nobel Lecture, December 8, 1981</ref> In parallel with Siegbahn's work, [[David W. Turner|David Turner]] at [[Imperial College London]] (and later at [[Oxford University]]) developed [[ultraviolet photoelectron spectroscopy]] (UPS) for molecular species using helium lamps.<ref>{{cite journal|doi=10.1063/1.1733134|title=Determination of Ionization Potentials by Photoelectron Energy Measurement|year=1962|last1=Turner|first1=D. W.|last2=Jobory|first2=M. I. Al|journal=The Journal of Chemical Physics|volume=37|pages=3007|bibcode = 1962JChPh..37.3007T|issue=12 }}</ref>