Grazing-incidence small-angle scattering

GISAS combines the accessible length scales of small-angle scattering (SAS: SAXS or SANS) and the surface sensitivity of grazing incidence diffraction (GID).

As a hybrid technique, GISAS combines concepts from transmission small-angle scattering (SAS), from grazing-incidence diffraction (GID), and from diffuse reflectometry.

With diffuse (off-specular) reflectometry it shares phenomena like the Yoneda/Vinyard peak at the critical angle of the sample, and the scattering theory, the distorted wave Born approximation (DWBA).

Thus GISAS gains access to a wider range of lateral and vertical structures and, in particular, is sensitive to the morphology and preferential alignment of nanoscale objects at the surface or inside the thin film.

As a particular consequence of the DWBA, the refraction of x-rays or neutrons has to be always taken into account in the case of thin film studies,[15][16] due to the fact that scattering angles are small, often less than 1 deg.

Specifically self-organization during MBE growth[2] and re-organization processes in block copolymer films under the influence of solvent vapor[3] have been characterized on the relevant timescales ranging from seconds to minutes.

Geometry of a GISAS experiment. The incident beam strikes the sample under a small angle close to the critical angle of total external x-ray reflection. The intense reflected beam as well as the intense scattering in the incident plane are attenuated by a rod-shaped beam stop. The diffuse scattering from the sample (red arrow) is recorded with an area detector. As an example the scattering from a block copolymer film with perpendicular lamellae is shown in the detector plane. The two lobes of scattering correspond to the lateral lamellar period of about 80 nm.