X-ray scattering techniques

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This is an X-ray diffraction pattern formed when X-rays are focused on a crystalline material, in this case a protein. Each dot, called a reflection, forms from the coherent interference of scattered X-rays passing through the crystal. X-ray diffraction pattern 3clpro.jpg
This is an X-ray diffraction pattern formed when X-rays are focused on a crystalline material, in this case a protein. Each dot, called a reflection, forms from the coherent interference of scattered X-rays passing through the crystal.

X-ray scattering techniques are a family of analytical techniques which reveal information about the crystal structure, chemical composition, and physical properties of materials and thin films. These techniques are based on observing the scattered intensity of an X-ray beam hitting a sample as a function of incident and scattered angle, polarization, and wavelength or energy.

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Note that X-ray diffraction is sometimes considered a sub-set of X-ray scattering, where the scattering is elastic and the scattering object is crystalline, so that the resulting pattern contains sharp spots analyzed by X-ray crystallography (as in the Figure). However, both scattering and diffraction are related general phenomena and the distinction has not always existed. Thus Guinier's classic text [1] from 1963 is titled "X-ray diffraction in Crystals, Imperfect Crystals and Amorphous Bodies" so 'diffraction' was clearly not restricted to crystals at that time.

Scattering techniques

Elastic scattering

Spectrum of various inelastic scattering processes that can be probed with inelastic X-ray scattering (IXS). Schematic IXS spectrum.png
Spectrum of various inelastic scattering processes that can be probed with inelastic X-ray scattering (IXS).

Inelastic X-ray scattering (IXS)

In IXS the energy and angle of inelastically scattered X-rays are monitored, giving the dynamic structure factor . From this many properties of materials can be obtained, the specific property depending on the scale of the energy transfer. The table below, listing techniques, is adapted from. [2] Inelastically scattered X-rays have intermediate phases and so in principle are not useful for X-ray crystallography. In practice X-rays with small energy transfers are included with the diffraction spots due to elastic scattering, and X-rays with large energy transfers contribute to the background noise in the diffraction pattern.

TechniqueTypical Incident Energy, keVEnergy transfer range, eVInformation on:
Compton scattering 1001,000Fermi Surface Shape
Resonant IXS (RIXS)4-200.1 - 50Electronic Structure & Excitations
Non-Resonant IXS (NRIXS)100.1 - 10Electronic Structure & Excitations
X-ray Raman scattering 1050 - 1000Absorption Edge Structure, Bonding, Valence
High resolution IXS100.001 - 0.1Atomic Dynamics, Phonon Dispersion

See also

References

  1. Guinier, A. (1963). X-ray diffraction in Crystals, Imperfect Crystals and Amorphous Bodies. San Francisco: W.H. Freeman & Co.
  2. Baron, Alfred Q. R (2015). "Introduction to High-Resolution Inelastic X-Ray Scattering". arXiv: 1504.01098 [cond-mat.mtrl-sci].