Effect of size and shape of crystallites on the optical properties of nanostructured ZnS films

The nanoparticles of ZnS is grown on the glass slide substrates using the thermal evaporation technique. The films are annealed in a vacuum ambient at temperatures between 300 and 550°C. The origin of anisotropic diffraction line broadening is studied using the modified Williamson-Hall plot. The shape and size of crystallites as well as the mean value of strain are studied by applying one of the powerful method of X-ray diffraction analysis i.e. Rietveld refinement procedure. It is found that, with the rise of annealing temperature, not only the size of crystallites increases, but also the shape of them changes from sphere to ellipsoid. The optical band gap are also studied from the transmittance and reflectance spectra of the films. The correlation between the microstructure and optical band gap are reported.