X-ray Scattering

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Basics

The term X-ray scattering refers to a group of techniques including small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS) and X-ray reflectivity. The technique of X-ray diffraction is also an X-ray scattering technique, but one applied to ordered, crystalline materials. X-ray scattering techniques are based on the interaction of X-rays with electrons of atoms. However, unlike diffraction, the X-rays are not scattered in patterns based on the crystallinity of the sample. Therefore, crystalline samples are not needed for measurement, and the technique is suitable for analysis of disordered materials. X-ray scattering thus lacks the detailed information obtained from diffraction, but this is offset by the technique's wider applicability over a range of samples.

Benefits

X-ray scattering techniques give information on the shapes, sizes and orientations of large molecules (e.g. proteins, enzymes, polymers) or particles of similar dimensions (nanoparticles, nanotubes, etc.), up to structures on the micrometre scale. For instance, the X-ray scattering technique will produce distinct and diagnostic curves from folded, partially unfolded, or completely unfolded proteins. The grazing-incidence small-angle X-ray scattering technique (GISAXS) is especially useful for gaining information on interface and surface structures of thin films. The high-intensity X-ray radiation available at DESY allows real-time measurements of dynamic processes, such as monitoring of structural changes of materials during stretching (devices for stretching samples under investigation are available at the HASYLAB SAXS facility).

Types of samples

Crystalline samples are not required for X-ray scattering techniques, and the samples can be liquids, solids, or combinations of these. The technique is also non-destructive, making it suitable for sensitive samples and samples where material is scarce.

Applications of X-ray scattering at DESY

The technique is mainly useful for measuring materials ranging from large molecules up to nanomaterials with micrometre superstructures, thus most applications lie in the areas of soft condensed matter (e.g. polymers, foams, gels), nanoscience and structural biology.

Examples of specific applications:

  • Determining the extent of folding in large protein molecules.
  • Determining the thickness and density of thin films.
  • Measuring the crystallinity of polymer samples.
  • In-situ monitoring of structural changes of materials under stress.
  • Real-time monitoring of industrial deposition processes such as ink-jet printing and the microscale deposition of materials for data storage devices.