Electrodeposition of CdSe nanocrystalline thin films at different deposition potentials

Cadmium selenide (CdSe) nanocrystalline thin films have been electrodeposited on ITO glass from aqueous electrolyte containing salts of cadmium sulfate and selenide dioxide. The crystal structure, surface morphology and optical properties are measured at the deposition potentials ranging from -600-700mV vs SCE. XRD analysis shows that the cubic CdSe nanophase is present in the thin films, the grain size increases with decreasing the deposition potential. AFM study shows that the films are characterized by the coalesced particles in slab or column shape for more positive potentials, while the surfaces of the films compose of inhomogeneous agglomerates for more negative potentials. The optical transmission study reveals, as the overvoltage increases, the transmission of the films decreases for the wavelength range 350-850 nm and the absorption edge moves to a long wavelength. The bandgap energy of all samples is larger than that of bulk CdSe and becomes smaller with decreasing grain size, indicating a quantum-size effect.