Working with grazing angle (I have seen it more often as GIXRD rather than GAXRD) can be useful also for nano powders if you want to maximize the signal (when you have a small quantity of powder spread on a surface).
Grazing angle technique can also refer to different configurations (and this creates a lot of confusion):
(i) fixed angle between specimen and incoming beam and 2theta scan
(ii) fixed angle between specimen and outgoing beam and theta scan
(iii) fixed angle between specimen normal and scattering vector, with conventional coupled scan. In this last case the grazing condition is obtained with angles close to pi/2 on a 4 circle gonio.
Not always it can be possible/convenient to work with a traditional instrument (i.e. 2theta arm scan at fixed specimen angle with respect to the incoming beam), especially for oriented thin films.
Be also warned though that this geometry (on a traditional instrument) introduces a lot of aberrations. The sampled volume, in fact, changes with the angle, unless you work with the condition (iii)
GAXRD = grazing or glancing angle x-ray diffraction
You irradiate at a very low incident angle to the sample surface. This gives you a large irradiated area and a low penetration depth into the sample. It is thus the technique of choice if you want to see only the surface of the sample, e.g. when studying thin film coatings.
Both are good it depends on your need. In case of nanoparticles you have large surface are or like bulk system so the GA-XRD may not very informative rather XRD which not have the small incidence angle limitation is useful.
As you want to study thin film diffraction pattern, you have only around 200 nm thick surface or less then that, therefore you have to have small angle incidence because the large angle may penetrate your film surface and you will get only substrate peak.
So both are good facilities but depends on need.
Working with grazing angle (I have seen it more often as GIXRD rather than GAXRD) can be useful also for nano powders if you want to maximize the signal (when you have a small quantity of powder spread on a surface).
Grazing angle technique can also refer to different configurations (and this creates a lot of confusion):
(i) fixed angle between specimen and incoming beam and 2theta scan
(ii) fixed angle between specimen and outgoing beam and theta scan
(iii) fixed angle between specimen normal and scattering vector, with conventional coupled scan. In this last case the grazing condition is obtained with angles close to pi/2 on a 4 circle gonio.
Not always it can be possible/convenient to work with a traditional instrument (i.e. 2theta arm scan at fixed specimen angle with respect to the incoming beam), especially for oriented thin films.
Be also warned though that this geometry (on a traditional instrument) introduces a lot of aberrations. The sampled volume, in fact, changes with the angle, unless you work with the condition (iii)
GAXRD can also be used to obtain information on the composition of material as a function of 'depth'. Using configuration (i) in Matteo Leoni's post, you can change the angle between the incident beam and the specimen and thus get a series of scans that show the depth profile of your material.
Both are good and the choice depends on what sample is being studied by XRD .
If it is a bulk sample then normal Bragg Brentano geometry would do the job, whereas if the sample is a thin film of nm order thickness then the GIXRD would do the job. Care should be taken to see that the diffraction pattern consists of only that of the sample rather that that of the substrate which may be quartz or something else. This is achieved by keeping the incident angle of the parallel beam low say less than 1 deg. In this condition the X-ray beam passes through the sample alone and one gets the diffraction pattern of the sample.
My understanding so far: There seems to be only one reason to use grazing incidence angle and that is to reduce the examination depth in the specimen. Now, depending on where you observe in reciprocal space (2ϴ), you may monitor various Nano structural periodicities existing within the sampling VOXEL including a few nm film thickness. XRR technique uses the data immediately surrounding the incident beam direction (0o 2ϴ). In the case of a thin film (irrespective of any "preferred orientation" or crystallinity), this would be a "spectral range" of typically 0 to 3o.
What I'm beginning to understand is that WAXS measurements may also be performed with the shallow angle of incidence to limit the depth of examination. This would require sensitive detectors and extended XRD signal integration times due to lower XRD intensity flux. Due to shallow incidence angle the contribution from the top layers goes up exponentially as does the sampling area. Especially, below 5o. The overall integrated intensity should still be conserved.
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