Size effect on the physical properties of CdS thin films prepared by integrated physical-chemical approach

Using an integrated physical-chemical approach, nanocrystalline cadmium sulfide (CdS) thin films were prepared by evaporating chemically synthesized CdS nanorods. Both the CdS nanorods and nanocrystalline thin films exhibited hexagonal wurtzite structure. Chemically synthesized CdS nanorods of about 7 nm average diameter were flexible, frequently folded to have elliptical cage linked chain structures and aggregate to form nanorod bundles. The bandgap energy of the nanocrystalline CdS films suffered a blue shift of about 0.07 eV due to intermediate quantum confinement of charge carriers. The reaction atmosphere was found to have strong effects on the particle size control of the nanostructures. Room temperature photoluminescence (PL) spectra of the films revealed a broad emission at about 429 nm related to recombination of excitons and shallowly trapped electron-hole pairs, along with the near-band-edge emission. Influence of particle size and defects on the structural and optical properties of CdS nanorods and nanocrystalline thin films are discussed.