Omega/Theta - Rocking curve measurement

 

 

The Rocking Curve of a crystal reflection indicates the quality of the crystalline lattice. This can be down pointwise for fast checking or in combination with a mapping tool to receive a quality map.

Measuring a Rocking Curve means measuring in Theta-scan mode, which requires a goniometer. A double crystal is brought into the primary beam path to decrease the spectral width and divergency. However, the side effect is a strongly reduced intensity. Therefore, the double crystal is mounted on a retractable holder to be able to switch it "on" or "off".

Rocking curves of a 6H SiC crystal measured along a line on spots of 8 mm distance

Rocking curves are primarily used to study defects such as dislocation density, mosaic spread, curvature, misorientation, and inhomogeneity.

In lattice matched thin films, rocking curves can also be used to study layer thickness, superlattice period, strain and composition profile, lattice mismatch, ternary composition, and relaxation.

In a perfect crystal, the width of the rocking curve is determined by the beam geometry and the spectral width of the source. Crystal imperfections cause a broadening of the rocking curve. Usually the half-width of the measured rocking curve is compared to the one calculated assuming a perfect crystal. With our instruments we can reach a minimum half-width of 0.002° (7 seconds).