Electron microscopy of layered single crystals grown by direct vapour transport method

Abstract

Besides interesting properties such as optical, transport, structure, etc. possessed by crystals of transition metal dichalcogenides, they have also been found to have a potential application in the fabrication ofpec solar cells. These crystals are normally grown by carrier gas transport technique but are always contaminated by carrier gases. A new method of direct vapour transport has been developed and successfully applied to grow these crystals including those of off-stoichiometric varieties.The crystals thus grown have been characterized structurally using the techniques of x-ray powder, rotation and Weissenberg photographs and electron diffraction. Perfection studies have been made by techniques like chemical etching and electron microscopy.This review describes the electron microscopic studies made on the single crystals of the layered compounds. High resolution technique of weak beam has been employed to study dislocation pattern. Dissociated dislocations have been used to estimate stacking fault energy. Such measurements have also been carried out at different temperatures and the variation of stacking fault energy with temperature has been worked out. Interesting information regarding phase transformation for TaS2 and W3Se4 in the temperature range 109 to 580 K has been derived from the electron diffraction studies and the implications have been discussed.