<title>X-ray diffraction properties of highly oriented pyrolytic graphite</title>

Abstract

The x-ray diffraction properties of highly oriented pyrolytic graphite (HOPG) were studied for x-ray energies ranging from 4 to 60 keV. In particular, the secondary extinction thickness was determined by recording the peak and integrated reflectivity as a function of depth below the surface. The results showed that for the high quality material investigated a thickness of 200 to 300 micrometers was sufficient to get 80% of the maximum reflectivity that is obtained for a very thick plate. Primary extinction was important for low energy and still persisted at higher energies. Inhomogeneities of the mosaic structure were observed, too, that make this material not a truly ideal mosaic monochromator crystal. However, quite high peak reflectivities between 35% and 58% were measured at FWHM of 0.25 to 0.45 degrees. A 200 micrometers thick plate was then prepared and glued on a bending device to manufacture a monochromator or analyzer with variable curvature that works from flat down to a minimum bending radius of 10 cm. The successful tests of this device confirmed that HOPG plates much thinner than those commonly used as x-ray monochromators and analyzers still have high efficiency and can be curved to achieve dynamical focusing.