Editing Synchrotron light source (section)

==Experimental techniques and usage==
Synchrotron light is an ideal tool for many types of research in [[materials science]], [[physics]], and [[chemistry]] and is used by researchers from academic, industrial, and government laboratories. Several methods take advantage of the high intensity, tunable wavelength, collimation, and polarization of synchrotron radiation at beamlines which are designed for specific kinds of experiments. The high intensity and penetrating power of synchrotron X-rays enables experiments to be performed inside sample cells designed for specific environments. Samples may be heated, cooled, or exposed to gas, liquid, or high pressure environments. Experiments which use these environments are called ''in situ'' and allow the characterization of atomic- to nano-scale phenomena which are inaccessible to most other characterization tools. ''In operando'' measurements are designed to mimic the real working conditions of a material as closely as possible.<ref>{{cite journal | last1=Nelson | first1=Johanna | last2=Misra | first2=Sumohan | last3=Yang | first3=Yuan | last4=Jackson | first4=Ariel | last5=Liu | first5=Yijin | last6=Wang | first6=Hailiang | last7=Dai | first7=Hongjie | last8=Andrews | first8=Joy C. | last9=Cui | first9=Yi | last10=Toney | first10=Michael F. |display-authors=5| title=In Operando X-ray Diffraction and Transmission X-ray Microscopy of Lithium Sulfur Batteries | journal=Journal of the American Chemical Society | volume=134 | issue=14 | date=2012-03-30 | doi=10.1021/ja2121926 | pmid=22432568 | pages=6337–6343}}</ref>

===Diffraction and scattering===
[[X-ray diffraction]] (XRD) and [[scattering]] experiments are performed at synchrotrons for the structural analysis of [[crystalline]] and [[amorphous]] materials. These measurements may be performed on [[Powder diffraction|powders]], [[single crystals]], or [[thin films]]. The high resolution and intensity of the synchrotron beam enables the measurement of scattering from dilute phases or the analysis of [[residual stress]]. Materials can be studied at [[high pressure]] using [[diamond anvil cell]]s to simulate extreme geologic environments or to create exotic forms of matter.{{Citation needed|date=January 2021}}
[[Image:010 large subunit-1FFK.gif|thumb|200px|left| Structure of a [[ribosome]] subunit solved at high resolution using synchrotron X-ray crystallography.<ref name=Ban2000>{{cite journal | last1=Ban | first1=N. |first2=P. |last2=Nissen|first3=J. |last3=Hansen |first4=P. |last4=Moore|first5= T. |last5=Steitz |title=The Complete Atomic Structure of the Large Ribosomal Subunit at 2.4 Å Resolution | journal=Science | volume=289 | issue=5481 | date=2000-08-11 | doi=10.1126/science.289.5481.905 | pmid=10937989 | pages=905–920| bibcode=2000Sci...289..905B }}</ref>]]

[[X-ray crystallography]] of [[proteins]] and other macromolecules (PX or MX) are routinely performed. Synchrotron-based crystallography experiments were integral to solving the structure of the [[ribosome]];<ref name=Ban2000 /><ref>The Royal Swedish Academy of Sciences, [https://www.nobelprize.org/nobel_prizes/chemistry/laureates/2009/popular-chemistryprize2009.pdf "The Nobel Prize in Chemistry 2009: Information for the Public"], accessed 2016-06-20</ref> this work earned the [https://www.nobelprize.org/nobel_prizes/chemistry/laureates/2009/ Nobel Prize in Chemistry in 2009].

The size and shape of [[nanoparticles]] are characterized using [[small angle X-ray scattering]] (SAXS). Nano-sized features on surfaces are measured with a similar technique, [[Grazing-incidence small-angle scattering|grazing-incidence small angle X-ray scattering]] (GISAXS).<ref>{{cite journal | last1=Renaud | first1=Gilles | last2=Lazzari | first2=Rémi | last3=Leroy | first3=Frédéric | title=Probing surface and interface morphology with Grazing Incidence Small Angle X-Ray Scattering | journal=Surface Science Reports | volume=64 | issue=8 | year=2009 | doi=10.1016/j.surfrep.2009.07.002 | pages=255–380| bibcode=2009SurSR..64..255R }}</ref> In this and other methods, surface sensitivity is achieved by placing the crystal surface at a small angle relative to the incident beam, which achieves [[total external reflection]] and minimizes the X-ray penetration into the material.{{Citation needed|date=January 2021}}

The atomic- to nano-scale details of [[Surface science|surfaces]], interfaces, and [[thin films]] can be characterized using techniques such as [[X-ray reflectivity]] (XRR) and [[X-ray crystal truncation rod|crystal truncation rod]] (CTR) analysis.<ref>{{cite journal | last1=Robinson | first1=I K | last2=Tweet | first2=D J | title=Surface X-ray diffraction | journal=Reports on Progress in Physics | volume=55 | issue=5 | date=1992-05-01 | doi=10.1088/0034-4885/55/5/002 | pages=599–651| bibcode=1992RPPh...55..599R | s2cid=250899816 }}</ref> [[X-ray standing wave]] (XSW) measurements can also be used to measure the position of atoms at or near surfaces; these measurements require high-resolution optics capable of resolving [[dynamical diffraction]] phenomena.<ref>{{cite journal | last1=Golovchenko | first1=J. A. | last2=Patel | first2=J. R. | last3=Kaplan | first3=D. R. | last4=Cowan | first4=P. L. |author5-link=Michael Bedzyk | last5=Bedzyk | first5=M. J. | title=Solution to the Surface Registration Problem Using X-Ray Standing Waves | journal=Physical Review Letters | volume=49 | issue=8 | date=1982-08-23 | doi=10.1103/physrevlett.49.560 | pages=560–563| bibcode=1982PhRvL..49..560G | url=https://dash.harvard.edu/bitstream/1/29407052/1/SolutionToTheSurfaceRegistrationProblem.pdf }}</ref>

Amorphous materials, including liquids and melts, as well as crystalline materials with local disorder, can be examined using X-ray [[pair distribution function]] analysis, which requires high energy X-ray scattering data.<ref>T. Egami, S.J.L. Billinge, "Underneath the Bragg Peaks: Structural Analysis of Complex Materials", [https://books.google.com/books?id=ek2ymu7_NfgC&pg=PP2 ''Pergamon'' (2003)]</ref>

By tuning the beam energy through the [[absorption edge]] of a particular element of interest, the scattering from atoms of that element will be modified. These so-called resonant anomalous X-ray scattering methods can help to resolve scattering contributions from specific elements in the sample.{{Citation needed|date=January 2021}}

Other scattering techniques include [[EDXRD|energy dispersive X-ray diffraction]], [[resonant inelastic X-ray scattering]], and magnetic scattering.{{Citation needed|date=January 2021}}

===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}}

===Imaging===
[[File:APS - Nanoprobe.jpg|thumb|right|X-ray nanoprobe beamline at the [[Advanced Photon Source]]]]
Synchrotron X-rays can be used for traditional [[X-ray imaging]], [[phase-contrast X-ray imaging]], and [[tomography]]. The Ångström-scale wavelength of X-rays enables imaging well below the [[diffraction limit]] of visible light, but practically the smallest resolution so far achieved is about 30&nbsp;nm.<ref>Argonne National Laboratory Center for Nanoscale Materials, [http://www.anl.gov/cnm/capabilities/x-ray-microscopy-capabilities "X-Ray Microscopy Capabilities"], accessed 2016-06-20</ref> Such [[Nanoprobe (device)|nanoprobe]] sources are used for [[scanning transmission X-ray microscopy]] (STXM). Imaging can be combined with spectroscopy such as [[X-ray fluorescence]] or [[X-ray absorption spectroscopy]] in order to map a sample's chemical composition or oxidation state with sub-micron resolution.<ref>{{cite journal | last1=Beale | first1=Andrew M. | last2=Jacques | first2=Simon D. M. | last3=Weckhuysen | first3=Bert M. | title=Chemical imaging of catalytic solids with synchrotron radiation | journal=Chemical Society Reviews | volume=39 | issue=12 | year=2010 | pages=4656–4672 | doi=10.1039/c0cs00089b | pmid=20978688 | hdl=1874/290865 | hdl-access=free }}</ref>