Editing Synchrotron light source (section)

===Spectroscopy===
[[X-ray absorption spectroscopy]] (XAS) is used to study the coordination structure of atoms in materials and molecules. The synchrotron beam energy is tuned through the absorption edge of an element of interest, and modulations in the absorption are measured. [[Photoelectron]] transitions cause modulations near the absorption edge, and analysis of these modulations (called the [[X-ray absorption near edge structure|X-ray absorption near-edge structure]] (XANES) or [[Near edge X-ray absorption fine structure|near-edge X-ray absorption fine structure]] (NEXAFS)) reveals information about the [[chemical state]] and local symmetry of that element. At incident beam energies which are much higher than the absorption edge, photoelectron scattering causes "ringing" modulations called the [[extended X-ray absorption fine structure]] (EXAFS). [[Fourier transformation]] of the EXAFS regime yields the bond lengths and number of the surrounding the absorbing atom; it is therefore useful for studying liquids and [[amorphous]] materials<ref>{{cite journal | last1=Sayers | first1=Dale E. | last2=Stern | first2=Edward A. | last3=Lytle | first3=Farrel W. | title=New Technique for Investigating Noncrystalline Structures: Fourier Analysis of the Extended X-Ray—Absorption Fine Structure | journal=Physical Review Letters | volume=27 | issue=18 | date=1971-11-01 | doi=10.1103/physrevlett.27.1204 | pages=1204–1207| bibcode=1971PhRvL..27.1204S }}</ref> as well as sparse species such as impurities. A related technique, [[X-ray magnetic circular dichroism]] (XMCD), uses circularly polarized X-rays to measure the magnetic properties of an element.{{Citation needed|date=January 2021}}

[[X-ray photoelectron spectroscopy]] (XPS) can be performed at beamlines equipped with a [[Photoemission spectroscopy|photoelectron analyzer]]. Traditional XPS is typically limited to probing the top few nanometers of a material under vacuum. However, the high intensity of synchrotron light enables XPS measurements of surfaces at near-ambient pressures of gas. Ambient pressure XPS (AP-XPS) can be used to measure chemical phenomena under simulated catalytic or liquid conditions.<ref>{{cite journal | last1=Bluhm | first1=Hendrik | last2=Hävecker | first2=Michael | last3=Knop-Gericke | first3=Axel | last4=Kiskinova | first4=Maya | last5=Schlögl | first5=Robert | last6=Salmeron | first6=Miquel | title=In Situ X-Ray Photoelectron Spectroscopy Studies of Gas-Solid Interfaces at Near-Ambient Conditions | journal=MRS Bulletin | volume=32 | issue=12 | year=2017 | doi=10.1557/mrs2007.211 | pages=1022–1030| osti=927255 | s2cid=55577979 | url=https://digital.library.unt.edu/ark:/67531/metadc900709/ }}</ref> Using high-energy photons yields high kinetic energy photoelectrons which have a much longer [[inelastic mean free path]] than those generated on a laboratory XPS instrument. The probing depth of synchrotron XPS can therefore be lengthened to several nanometers, allowing the study of buried interfaces. This method is referred to as high-energy X-ray photoemission spectroscopy (HAXPES).<ref>{{cite journal | last1=Sing | first1=M. | last2=Berner | first2=G. | last3=Goß | first3=K. | last4=Müller | first4=A. | last5=Ruff | first5=A. | last6=Wetscherek | first6=A. | last7=Thiel | first7=S. | last8=Mannhart | first8=J. | last9=Pauli | first9=S. A. | last10=Schneider | first10=C. W. | last11=Willmott | first11=P. R. | last12=Gorgoi | first12=M. | last13=Schäfers | first13=F. | last14=Claessen | first14=R. | title=Profiling the Interface Electron Gas of LaAlO<sub>3</sub>/SrTiO<sub>3</sub> Heterostructures with Hard X-Ray Photoelectron Spectroscopy | journal=Physical Review Letters | volume=102 | issue=17 | date=2009-04-30 | doi=10.1103/physrevlett.102.176805 | page=176805| pmid=19518810 | arxiv=0809.1917 | bibcode=2009PhRvL.102q6805S | s2cid=43739895 }}</ref> Furthermore, the tunable nature of the synchrotron X-ray photon energies presents a wide range of depth sensitivity in the order of 2-50 nm.<ref>{{Cite journal |last1=Gong |first1=Zhengliang |last2=Yang |first2=Yong |date=2018 |title=The application of synchrotron X-ray techniques to the study of rechargeable batteries |url=https://linkinghub.elsevier.com/retrieve/pii/S2095495617311877 |journal=Journal of Energy Chemistry |language=en |volume=27 |issue=6 |pages=1566–1583 |doi=10.1016/j.jechem.2018.03.020|s2cid=104038441 |url-access=subscription }}</ref> This allows for probing of samples at greater depths and for non destructive depth-profiling experiments.

Material composition can be quantitatively analyzed using [[X-ray fluorescence]] (XRF). XRF detection is also used in several other techniques, such as XAS and XSW, in which it is necessary to measure the change in absorption of a particular element.{{Citation needed|date=January 2021}}

Other spectroscopy techniques include [[angle resolved photoemission spectroscopy]] (ARPES), [[soft X-ray emission spectroscopy]], and [[nuclear resonance vibrational spectroscopy]], which is related to [[Mössbauer spectroscopy]].{{Citation needed|date=January 2021}}