Rocking curve measurement

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.

A rocking curve is recorded by moving the diffractometer into a reflecting position and then scanning the shape of reflection curve. The diffractometer motion sequence is similar to the Theta Scan. Additionally a special collimator, e.g. a double crystal is placed in the primary beam path to reduce the influence of the divergence and spectral width of the beam.

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 with that calculated  for a perfect crystal. With our instruments we can reach a minimum half-width of 0.002° (7 seconds).