GISAXS stands for Grazing-Incidence Small-Angle X-ray scattering and is a scattering technique most commonly done at synchrotron radiation facilities. A related technique also exists for neutron scattering (GISANS). 

Contents [hide]
1 GISAXS applications
2 GISAXS analysis
3 References 
4 External links 


[edit] GISAXS applications

GISAXS is a powerful tool to study nanostructured surfaces and thin films, combining the accessible length scales of small-angle x-ray scattering (SAXS) and the surface sensitivity of grazing-incidence diffraction (GID). Application range from the characterization of quantum dot arrays and growth instabilities formed during in-situ growth, as well as self-organized nanostructures in thin films of block copolymers, silica mesophases, and nanoparticles.


[edit] GISAXS analysis

As a hybrid technique, GISAXS combines concepts from transmission SAXS and from GID. From SAXS it uses the form factors and structure factors. From GID it uses the scattering geometry close to the critical angles of substrate and film, and the two-dimensional character of the scattering, giving rise to diffuse rods of scattering intensity perpendicular to the surface. GISAXS also shares elements of the scattering technique of diffuse reflectivity such as the Yoneda/Vinyard peak at the critical angle of the sample, and the scattering theory, the so-called distorted wave Born approximation (DWBA). However, while diffuse reflectivity remains confined to the incident plane (the plane given by the incident beam and the surface normal), GISAXS explores the whole scattering from the surface in all directions, typically utilizing an area detector. Thus GISAXS gains access to a wider range of lateral 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 has to be always taken into account, due to the fact that scattering angles are small, often less than 1 deg. The refraction correction applies to the perpendicular component of the scattering vector with rfespect to the substrate while the parallel component is unaffected. Thus parallel scattering can often be interpreted within the kinematic theory of SAXS, while refractive corrections apply to the scattering along perpendicular cuts of the scattering image, for instance along a scattering rod.

Another complication arises in the scattering from low-Z films e.g. organic materials on silicon wafers, when the incident angle is inbetween the critical angles of the film and the substrate. In this case, the reflected beam from the substrate has a similar strength as the incident beam and thus the scattering from the reflected beam from the film structure can give rise to a doubling of scattering features in the perpendicular direction. This as well as inteference between the scattering from the direct and the reflected beam can be fully accounted for by the DWBA scattering theory.

These complications are often more than offset by the fact that the dynamic enhancement of the scattering intensity is significant, and thus in-situ and real-time experiments are facilitated.


[edit] References

^ <ref>http://staff.chess.cornell.edu/~smilgies/gisaxs/GISAXS.php</ref>


[edit] External links

<ref>http://staff.chess.cornell.edu/~smilgies/gisaxs/GISAXS.php</ref>
<ref>http://www.gisaxs.de/index.html</ref>
<ref>http://www.insp.jussieu.fr/axe2/Oxydes/IsGISAXS/isgisaxs.htm</ref>