Method of grazing incidence (GI-XRD)

For the X-ray diffraction study of thin films the grazing incidence technique is applied in order to enhance the sensitivity for scattering contributions from the film and suppress substrate scattering. At low incidence angles the absorption mainly limits the penetration depth of the radiation (thickness for reduction of primary intensity to 1/e) and hence the information depth in the experiment.


Fig. 1: 
Penetration depth of Cu-radiation for different materials in dependence on incidence angle.

Using this method the autofocussing of the X-rays in a standard diffractometer is lost; the by the X-ray beam illuminated area depends directly on the incidence angle. Therefore a Kollimator is located in the scattered beam in front of the detector. The instrumental resolution (FWHM) is now determined by the opening angle of the Kollimator. It is about 3 times larger than for powder diffraction. 


Fig. 2: 
Scheme of the measuring arrangement for thin film studies by X-ray diffraction.

Thin film diffractometers are very often equipped with a Göbel-mirror besides primary slits.The mirror collimates the divergent radiation from the tube. This results in an intensity gain by a factor of 4 to 7.