Graphite monochromator crystals are commonly used in X-ray diffraction work because of their high efficiency and mosaic crystal characteristics. The commercially available graphite monochromator crystals, which are produced by high temperature pyrolysis followed by compression annealing, have certain minimum mosaic spreads. An increasing number of high resolution applications now demand graphite crystals that have lower mosaic spread, to better match the small angular divergence of the X-ray optics. Halving the mosaic spread can double the X-ray intensity in certain protein crystallography applications. It has been demonstrated that graphite deposits produced by low temperature pyrolysis have favorable graphite microstructure, and ESLI has grown planar deposits of such epitaxial material in sizes suitable for X-ray monochromator applications. It is expected that compression annealing these epitaxial deposits will produce graphite monochromator crystals with improved mosaic spread. We propose to vapor deposit planar graphite using low temperature processes, compression anneal the deposits at high temperature, and measure the resulting mosaic spread. The goal of this program is to achieve significantly lower mosaic in graphite crystals than currently available. The proposed process may also head to improved curved crystal monochromators and to monochromator crystals having tailored anisotropic mosaic spread potentially useful in synchrotron sources.
