By executing a 2θ-Ω-Scan only the length of the scattering vector is varied by rotating the sample around the ω-axis (gure 15(b)) and by simultaneously rotating the detector on the rocking cantilever with twice the angular velocity. The direction at which the scattering vector is pointing therby remains unchanged. For symmetrical reexes Ω = θ and therefore the scan direction is along q⊥ (gure 18(a)). Particulariy this scan along q⊥ is useful to check if there are other crystalline phases incorporated in the crystal, which is true if other than the expected reexes are observed. Moreover, the occurrence of forbidden reexes hints at structural disorder in the examined crystal.
In this laboratory exercise we investigate thin lms grown on a substrate. For columnar growth (gure 10) the vertical coherence length, i. e. the length of the crystallites that scatter the incident X-ray beam coherently, is limited by the layer thickness. As a consequence the integral