OPTIMIZATION OF THE TECHNIQUE OF SYNTHESIS OF WSE2 THIN-FILMS BY SOLID-STATE REACTION BETWEEN W AND SE THIN-FILMS

WSe2 coatings were obtained by solid state reaction, induced by annealing under Se pressure, between the W and Se constituents in thin film form. The films have been investigated using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and optical absorption. Although stoichiometric WSe2 films in the hexagonal form were obtained, pinholes and cracks in the films were also observed. The effects of the annealing conditions (duration and temperature) on the orientation, crystallite grain size and residual inhomogeneities have been investigated. The films present the 2H-WSe2 hexagonal structure with a c axis of length 1.2974 +/- 0.0005 nm. All the films are found to be preferentially oriented with the c axis perpendicular to the plane of the substrate. The degree of preferential orientation is found to increase slightly with increasing annealing time. In general, the grain size is found to increase with increasing annealing time and temperature, but the density of pinholes, cracks and protrusions also increases. The optimum annealing temperature and duration appear to be approximately 773 K and 72 h respectively, at which values the grain size and orientation are maximum and the residual inhomogeneities are minimum. These films present good optical properties, similar to those of single crystals.