Optical and dielectric properties of PVA capped nanocrystalline PbS thin films synthesized by chemical bath deposition

Nanoparticles of lead sulfide (PbS) have been grown within the pores of polyvinyl alcohol (PVA) matrix on glass substrates by chemical bath deposition at and below room temperature (30 degrees C). Lead acetate and thiourea, dissolved in an alkaline medium, were taken as the sources of lead and sulfur. X-ray diffraction and selected area electron diffraction studies confirmed the cubic nanocrystalline PbS phase formation. Transmission electron micrograph of the films revealed the particle size lying in the range 10-20 nm. X-ray photoelectron spectroscopic studies confirmed the presence of lead and sulfur in the films, and their atomic ratios were found to be dependent on the deposition temperature. UV-vis spectrophotometric measurement showed a direct allowed band gap lying in the range 2.40-2.81 eV, which is much higher than the bulk value (0.41 eV). The band gap decreases with the increase of deposition temperature. The dielectric constant of the PVA-capped nanocrystalline PbS was in the range 155-265 at higher frequencies, which is much higher compared to only PVA and bulk PbS. (C) 2008 Elsevier B.V. All rights reserved.