Background
Single crystal MgO has been widely used as substrate material for the deposition of high quality oxide thin films, including semiconducting, superconducting, dielectric, ferroelectric, and ferromagnetic oxides. The quality of the oxide films is strongly correlated to the quality of the MgO substrate. Often, the peak width of an X-ray rocking curve is used as a quantitative indicator of the crystal quality, which measures the tilt spread of the out-of-plane lattices. Information about the twist spread of the in-plane lattices is, however, missing from the rocking curve measurement.
Investigation
Pole figure measurements, on the other hand, capture both the tilt and twist spread of a crystal in a single measurement because it involves both tilting and rotating (twisting) of the crystal during measurement. Results are presented in a two-dimensional map. The SmartLab multipurpose diffractometer, along with the Guidance data acquisition software, makes the pole figure measurement completely automated, from optics alignment to sample alignment and data collection.
In the figure below, the texture of a commercially available MgO substrate is analyzed using the (111) pole figure. Clearly, the crystal is cubic, showing a nice four-fold symmetry. The (111) peak width, along both the radial (tilt) and circular (twist) direction, is about 5°. This means the crystal is not perfect. There is a 5° mosaicity along both the out-of-plane and in-plane directions.
