Topography

J. Haertwig (Grenoble) surveyed the state of topographic imaging with third-generation synchroton radiation at ESRF Grenoble, the various methods, their instrumentation, and applications to problems of solid state physics and material science. The high intensity of synchroton radiation (up to 100 keV), and its large spatial coherence allow imaging by phase contrast radiography and (3D) tomography in a simple way. Y. Epelboin (Paris) described 'the topographic suite' of programs for the simulation of x-ray topographic images for various topographic settings and optical characteristics of the radiation source.

The benefits of the long beamline (80 m) of the Topography Station at SRS Daresbury with its small vertical divergence for topographic reticulography were demonstrated by A.R. Lang (Bristol). In this method a fine absorbing mesh is placed behind the crystal and projected by the diffracted beam on a photographic plate with varying distance to the mesh. The distortions of the mesh shadow allow determination of the orientation differences between crystal segments of the probe. A reticulograph of a giant screw dislocation in SiC allowed determination of the handedness of the screw.

M. Dudley (Stony Brook) reported on whitebeam synchroton topographic studies of hollow-core superscrew dislocations in 4H- and 6H-SiC single crystals. A novel topographic procedure to determine the point-to-point lattice parameter variations near the crystal surface was introduced by A.E. Voloshin (Moscow). The method is based on computer processing of plane-wave topographs obtained with conventional X-rays and allows d-value mapping on large specimen areas with spatial resolution of 3-10 m and high sensitivity to lattice distortions. The technique was applied to the study of KDP-type crystals grown from aqueous solution.

The last contribution (N. Goswami, New Delhi) dealt with the conventional X-ray topography and high-resolution diffractometry study of coiled GaAs membranes produced for force sensor applications.

H. Klapper