CdS nanoparticles grown in a polymer matrix by chemical bath deposition

Nanocrystallites of CdS have been grown by chemical bath deposition within the pores of poly(vinyl alcohol) (PVA) on glass and Si substrates. The CdS-PVA composite films are transparent in the visible region. XRD and TEM diffraction patterns confirmed the nanocrystalline CdS phase formation. TEM study of the film revealed the manifestation of nano CdS phase formation and the average particles size was varied in the range 5-12 nm. UV-vis spectrophotometric measurement showed high transparency (nearly 80% in the wavelength range 550-900 nm) of the films with a direct allowed band gap lying in the range 2.64-3.25 eV. Particle sizes have also been calculated from the shift of band gap with respect to that of bulk value and were found to be in the range 3.3-6.44 nm. The high dielectric constant (lies in the range 120-250 at high frequency) of PVA/CdS nanocomposite compared to that of pure PVA (-28) has been observed. The dielectric constant decreases with increase of dispersibility of the CdS nanoparticles within PVA. The nanocrystalline PVA/CdS thin films have also showed field emission properties with a turn-on field of approximately 6.6 V/microm, whereas only PVA thin film and bulk CdS on PVA have shown no field emission.