This might sound a stupid question. What is the difference in terms of information that can obtained between GI-SAXS and SAXS besides the fact that GI-SAXS can be used to look at in-plane and out of plane information? To look at thin film, does it mean i need use GI-SAXS rather than SAXS?
In terms of information, GI-SAXS is better for thin films because it increase the amount of information/feedback coming from film. Then, information from underlayer/substrate does not "cover" so much data from film. Therefore, GI-SAXS is more like in-plane technique.
The reply to your question depends on the information you want to obtain, the scattering properties of the film, the film thickness and it's support.
Both versions of this technique have their advantages and disadvantages.
GI-SAXS is mostly performed using a point source which compared to a line source with similar brilliance requires significantly longer measurement times. Additionally you have to be able to position the sample correctly (at at suitable grazin angle) to get a GI signal.
Standard SAXS alignment is much simpeler, can be done with a line source (which implies you have to desmear the data, or use smeared models), giving you much more scattered counts on the detector, but cannot record resolvable 2D scattering images en hence decreases the amount of info you can get from your scattering profile.
In short, if you don't need info which you can only obtain from 2D profiles and have a film which scatters strongly, the normal SAXS experiment is much simpeler and faster.
SAXS is a technique to study particles dissolved in solution, powders or in the bulk. GI-SAXS is used to characterize particles distributed over a surface. For thin film without particles is better to use ellipsometry and X-ray reflectometry.
Saxs is a transmission measurement and probes the structure in a volume - or you hit the film sample in the normal direction and probe the lateral structure. Gisaxs hits a film sample at grazing angles and mixes a depth information with the lateral structure. The wave field in the normal direction can be rather complicated and is often modeled for a detailed analysis - ie how the depth information is coded.
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