Synchrotron x-ray reticulography: principles andapplications

Abstract

Synchrotron x-ray reticulography is a versatile new technique for mapping misorientations in single crystals. It is nearly as simple to perform as conventional single-crystal Laue topography, yet it yields quantitative data on misorientations that would demand long sequences of images if the double-crystal technique were applied. In reticulography a fine-scale x-ray absorbing mesh is placed between a Laue-diffracting crystal specimen and the topograph-recording photographic plate. The mesh splits the diffracted beam into an array of individually identifiable microbeams. Direction differences between microbeams, which give the orientation differences between the crystal elements reflecting them, are measured from their relative shifts within the array when mesh-to-plate distance is changed. The angular sensitivity of reticulography depends upon the angular size of the x-ray source. At Station 7.6 at the SRS, Daresbury, 80 m from the tangent point, and with source size FWHM (full width half maximum) = 0.23 mm vertically, the incidence angular range in the vertical plane is only 0.6 arcsec, and misorientations down to this magnitude are measurable. Applications of reticulography to three quite different problems are described, illustrating the method's versatility. The problems are: (1) measuring surface lattice-plane tilts due to an array of dislocations in a large synthetic diamond; (2) determining the sense of the Burgers vector of a giant screw dislocation in SiC; and (3) measuring lattice curvature above an energetic ion implant in a natural diamond.