The mixed compounds of Transition metal dichalcogenides MX2 (M = Mo, W; X = S or Se) are semiconducting compounds exhibiting a layered structure. These compounds consist of weakly coupled sandwiched layers i.e. X – M – X in which M atom layer is enclosed within two X chalcogenes layers. The metal atom is always coordinated by six chalcogene atoms octahedrally or trigonally. The Molybdenum diselenide, tungsten diselenide and mixed compounds of molybdenum and tungsten diselenides are diamagnetic indirect semiconductors belonging to this family. These materials have been widely used as PEC solar cells, catalysts and also as good lubricants. TMDC compounds have been grown by direct vapour transport technique using a two zone furnace from stoichiometric mixture of molybdenum (99.95% pure), tungsten (99.99% pure) and selenium (99.9 % pure). The source zone and growth zone temperatures were 10750C and 10550C respectively. The grown crystals were found to be gray and shiny irregular platelets. The average crystal dimensions were 3-10mm2 in cross sectional area and few micrometers in thickness. The structural and physical surface features of as-grown crystals have been studied with the help of X-ray diffraction (XRD), Optical Microscopy and Scanning Electron Microscopy (SEM) techniques. The crystals grown by direct vapour transport technique possess 2H-hexagonal structure having /mmc space group and also contain only a little proportion of 3R polytype form. The optical micrograph shows the presence of screw dislocation on the surface of the grown crystals, which is clearly an indication that the growth of present materials in the form single crystals takes place via screw dislocation mechanism. Also the simultaneous presence of 2H and 3R polytypes is clearly seen in the optical micrograph, which confirms the results of XRD. The scanning electron micrographs show the presence of hexagonal crystallites on the surface of as grown crystals. Such crystallites form island on the as-grown surface where other units come and sit. However, the size and properties of grown crystals as well as the surface morphology has been found to depend on the growth conditions e.g. temperature profile, heating and cooling rate, duration of growth process etc.

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1. Electrical, Optical and Surface Microtopographic studies of Mo_0.25W_0.75Se₂ Single Crystals grown by DVT Technique
2. Optical Absorption in  Mo_xW_1-XSe₂ (x=0, 0.25, 1) Single Crystals
3. Growth and Surface Studies of Mo_XW_1-xSe₂ Crystals