Editing X-ray photoelectron spectroscopy (section)

=== Laboratory based XPS ===
In laboratory systems, either 10–30&nbsp;mm beam diameter non-monochromatic Al K<sub>α</sub> or Mg K<sub>α</sub> anode radiation is used, or a focused 20-500 [[micrometre|micrometer]] diameter beam single wavelength Al K<sub>α</sub> monochromatised radiation. Monochromatic Al K<sub>α</sub> X-rays are normally produced by diffracting and focusing a beam of non-monochromatic X-rays off of a thin disc of natural, crystalline [[quartz]] with a [[Miller index|<1010> orientation]]. The resulting wavelength is 8.3386 angstroms (0.83386&nbsp;nm) corresponding to a 1486.7 eV photon energy. Aluminum K<sub>α</sub> X-rays have an intrinsic [[#Full Width at Half Maximum (FWHM)|full width at half maximum (FWHM)]] of 0.43 eV, centered at 1486.7 eV (''E''/Δ''E'' = 3457).{{citation needed|date=July 2019}} For a well–optimized monochromator, the energy width of the monochromated aluminum K<sub>α</sub> X-rays is 0.16 eV, but energy broadening in common electron energy analyzers (spectrometers) produces an ultimate energy resolution on the order of FWHM=0.25 eV which is the ultimate energy resolution of most commercial systems. Under practical conditions, high energy-resolution settings produce peak widths (FWHM) between 0.4 and 0.6 eV for various elements and some compounds. For example, in a spectrum obtained for one minute at 20 eV pass energy using monochromated aluminum K<sub>α</sub> X-rays, the Ag 3''d''<sub>5/2</sub> peak for a clean silver film or foil will typically have a FWHM of 0.45 eV.{{citation needed|date=July 2019}} Non-monochromatic magnesium X-rays have a wavelength of 9.89 angstroms (0.989&nbsp;nm) which corresponds to a photon energy of 1253 eV. The energy width of the non-monochromated X-ray is roughly 0.70 eV, which is the ultimate energy resolution of a system using non-monochromatic X-rays.{{citation needed|date=July 2019}} Non-monochromatic X-ray sources do not use any crystal to diffract the X-rays allowing all primary X-rays lines and the full range of high-energy [[Bremsstrahlung]] X-rays (1–12 keV) to reach the surface. The ultimate energy resolution (FWHM) when using a non-monochromatic Mg K<sub>α</sub> source is 0.9–1.0 eV, which includes some contribution from spectrometer-induced broadening.{{citation needed|date=July 2019}}