Scattering features

Scattering experiments (x-ray or neutron) generates images which can be thought of as the Fourier transform of the material's realspace structure. I.e. the image is a slice through a conceptual 3D reciprocal-space. Although a scattering pattern can be arbitrarily complex, there are usually various features that can be analyzed separately, and from which one can learn much about a sample's structure. In particular, samples with well-defined structural order give rise to distinct scattering features, such as sharp rings or even distinct spots on the area detector image.

Rings

TBD

Example SAXS with a distinct isotropic ring (AgBH)

Spots

A sharp spot on a 2D detector is typically a Bragg peak: i.e. diffraction at a well-defined angle due to a realspace lattice. An array of sharp spots typically indicates that the sample is a single-crystal (or at least oriented; e.g. in-plane powder).

Diffuse Scattering

Many samples will exhibit diffuse scattering: scattering intensity over a broad range of angles, without a distinct peak or maximum. This kind of scattering usually comes from disorder within the sample. For instance, low-q diffuse scattering can come from nanoscale or microscale porosity, or from surface roughness in GISAXS. High-q diffuse scattering can arise from the defects in atomic lattices (and from the thermal motion of atoms in a lattice). Although one can generally assign diffuse scattering to some kind of disorder, it is difficult to make an unambiguous link, because there are many effects that can generate diffuse scattering.

Bragg Rods

TBD

Yoneda Streak

TBD

Speckles

TBD

See Also

• Tutorial:Qualitative_inspection