Synthesis and optical characterization of polymer-capped nanocrystalline ZnS thin films by chemical process

ZnS nanocrystals have been grown into the nanopores of polyvinyl pyrrolidone (PVP) matrix on glass and Si substrates by a simple wet-chemical route. X-ray diffraction (XRD) study confirmed the formation of cubic phase of ZnS nanocrystals into the polymer matrix. The particle size variation was achieved by varying the polymer mole fraction in the starting solution. Transmission electron microscopic image as well as XRD studies confirmed the nanometer size particles formation within the polymer matrix. The average particle size was found to lie in the range of 4-7 nm. UV-Vis NIR optical spectra showed the 90-95% transmittance in the visible and also in the near infrared region. The direct optical bandgap of the polymer-capped nano-ZnS film was lying in the range 3.87-3.98 eV for different PVP fractions in the film. The direct band gap values are higher than the bulk value (3.6 eV) and the increment of bandgap also supports the nanometer size ZnS particle formation within the polymer matrix. The high-frequency dielectric constant (8) of the PVP-ZnS nanocomposite has been measured and the values lies in the range 50-90 which is much higher than that of only PVP having a dielectric constant similar to 28. The dielectric constant decreases as the dispersibility increases. (c) 2006 Elsevier B.V. All rights reserved.