Under the generic name of grazing incidence diffraction, several techniques are comprised: Grazing Small and Wide Angle Scattering (GISAXS & GIWAXS), Grazing Incidence Diffraction (GID) and Surface X-ray diffraction (SXRD), althought this nomenclature is not universal. In grazing incidence techniques, the X-ray beam impinges on the surface at a very small angle with respect to the surface plane. By modifying the incidence angle, the penetration depth of the X-ray beam in the sample can be controlled, and thus, at very shallow angles (typically below 1°), the signal coming from the surface area is maximised.
GISAXS is a variant of SAXS in which the small angle scattering from a surface is measured. In GIWAXS, one measures the wide angle scattering. These two techniques are generally used to study surfaces and interfaces of non-crystalline materials (see for example here, and references therein). They can also be used to study buried and internal structures.
GID and SXRD are used to study the structure of crystalline surfaces and interfaces. GID is usually, but not exclusively, done in grazing incidence and exit geometry. GID is employed to determine the lattice parameters and strain in films and at interfaces. Typically the signal close to Bragg peaks is measured. In SXRD, the so-called crystal truncation rods (CTRs) are measured. From the intensity measured between Bragg peaks along the direction perpendicular to the surface, the atomic structure of surfaces, films or interfaces can be determined. For that, initial models are refined using adequate software, such as GenX, ROD or WinROD.