Structural phase transformation and modification of optical absorption of SHI induced nanostructured CdS films

Abstract

Nanostructured CdS films are prepared on glass substrates by chemical bath deposition (CBD) method at room temperature and the samples are subjected to 120 MeV Ag9+ SHI irradiation at various fluences from 1 × 1011 to 3 × 1013 ions/cm2. Analysis of the samples by XRD exhibits both pristine as well as irradiated films are of cubic phase structure and shifting of diffraction peaks towards lower diffraction angle is observed upon irradiation. Structural phase transition from cubic to hexagonal is observed for the sample at high fluence 3 × 1013 ions/cm2. Crystallite size is found to increase for irradiated samples. Surface morphology observed using AFM shows that films consist of several nanoparticles (grains) and several small grains of CdS nanoparticles are grouped to form cluster. Increase in grain size due to irradiation is also observed from AFM picture. The optical absorption spectra exhibit shift in the fundamental absorption edge and hence the optical band gap energy decreases but the refractive index as well as dielectric constant increase with increasing ion fluence. Two intense and one weak Raman lines for pristine as well as irradiated CdS have been observed and all the samples show shift in Raman lines relative to bulk CdS due to phonon localization.