Absolute measurement of lattice parameter in single crystals and epitaxic layers on a double-crystal X-ray diffractometer

Details of the recently developed `zone technique' for the absolute measurement of lattice parameter and strain in single-crystal solids and thin films are presented. The method is based on measuring X-ray rocking curves from a few equatorial planes within a suitable zone and correcting their peak positions at once with a single zero offset. In contrast to the comparative method, which usually requires use of two opposite azimuthal directions, those in the zone technique can often be completed in only one azimuthal setting. A typical strained layer in the cubic system can be fully and rapidly characterized with only three rocking curves. The technique is suitable for routine applications under typical laboratory conditions, and for high-precision measurements of nearly perfect crystals in a controlled environment, with a potential parts in 10 million accuracy. This degree of accuracy is a direct consequence of the zero offset correction procedure, which effectively cancels a large portion of the misalignment errors in the diffractometer. The use of the (n,−n) geometry substantially reduces the errors of eccentricity compared to the Bond technique, and its stronger reflections enable the measurement of small samples about 0.05 mm in length with relative ease. The technique is illustrated with examples, and its extension to the triple-axis (ω–2θ) instruments is discussed.