Figure 1: GISAXS geometry (click here for original publication with a fundamental view on GISAXS and its properties)
Grazing incidence small-angle X-ray scattering (GISAXS) is a powerful technique for analyzing nanoscale surface structures and thin-film morphologies. It is especially useful as a rapid method under challenging sample conditions and as a complementary approach to direct imaging techniques. Direct microscopy methods are commonly used to characterize surface morphology and the lateral spacing of surface features. However, these techniques are limited by their very small observable area and their inability to probe buried or internal structures. Additional constraints include the need for vacuum and electrical conductivity in electron microscopy, as well as the limited scanning speed of AFM. GISAXS overcomes many of these limitations, as it can be performed under ambient conditions, and each scattering pattern can be recorded within just a few seconds (depending on scattering contrast and beam intensity). These characteristics make GISAXS particularly attractive for investigating dynamic structural changes in physical and chemical processes occurring at surfaces and within films.
In recent years, the number of GISAXS studies has increased significantly, driven by the availability of this technique at many synchrotron radiation facilities. Furthermore, advances in high-brilliance laboratory X-ray sources now allow GISAXS to be performed in smaller, laboratory-scale setups. Although these compact systems typically offer lower resolution and slower data acquisition, they often provide sufficient performance for many applications. The method is now well established, and the angular resolution of scattering experiments has been improved through the use of smaller, low-divergence beams. As with all X-ray scattering techniques, monochromatic X-rays provide information about electron density fluctuations within the illuminated area of the sample. The photon energy is typically in the range of 5 to 20 keV, offering a favorable scattering-to-absorption ratio. For soft-matter samples, an energy around 8 keV is generally optimal, whereas higher energies are recommended for materials containing heavier elements.
For the investigation of coatings, films, and surface-supported particles, GISAXS offers several advantages over transmission-based scattering methods. A highly intense scattering pattern can be obtained even from nanoscale-thick films, as the X-ray beam travels a sufficiently long path within the film plane. Length scales from a few to several hundred nanometers are accessible without the limitations imposed by beamstops that block the region near q ≈ 0 in transmission geometries. This is due to the ability to perform out-of-plane scans in the GISAXS configuration. Bulk scattering from the substrate is reduced because the penetration depth of the incident beam is limited at grazing angles close to the substrate’s critical angle. Sample preparation methods such as spin coating, dip coating, drop casting, or sputtering are well established. GISAXS can be employed to determine both the internal morphology of thin films and the surface morphology of films, coatings, and substrates. .