Structural and optical modifications of CdS properties in CdS-Au thin films prepared by CBD

In this work highlights the modifications of the crystalline structure and properties of the nanostructured cadmium sulphide (CdS) thin films, including gold quantum dots grown to form a hybrid metal-semiconductor system. By means of chemical bath deposition (CBD) good quality thin films are obtained, with the advantage of doping in-synthesis with no required additional steps. Film thicknesses around 100 nm were determined by ellipsometry. The binding energies of elements in the CdS and CdS-Au samples were measured by X-ray photoelectronic spectroscopy (XPS). The materials crystalline structure was studied by X-ray diffraction (XRD). A change from disperse like-single-crystalline (highly oriented) CdS NP’s films to monodisperse CdS NP’s–Au QD’s like-single-crystalline samples was observed. This behaviour was confirmed by TEM micrographs. The samples properties pass from an intermediate quantum confinement regime (IQCR) in CdS to a strong one (SQCR) in CdS-Au. The Raman vibrational spectra allowed the analysis of the phonon emissions in CdS, where the Raman shift gives structural information and confirms the effects of IQCR in CdS and the SQCR in CdS-Au. The optical UV–Vis characterization describes the effect of the structural modifications, with an optical band gap shift at higher energy in the CdS-Au sample related to the SQCR. Photoluminescence (PL) measured at room-temperature shows a decrease of PL intensity in CdS-Au film due to via defects-recombination, with respect to that in CdS. This fact is interpreted as an effect of a decreasing of surface defects due to passivation by the Au presence.