Nanostructured cadmium sulphide thin films by XPS

Nanostructured cadmium sulfide thin films were deposited on SiO2 by a cold-wall low-pressure CVD reaction system starting from the single-source precursor Cd(O-iPrXan)2 [O-iPrXan = S2COCH(CH3)2]. Deposition experiments were carried out in an inert nitrogen atmosphere in optimized pressure/gas flow conditions. The obtained films were analyzed by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) for a detailed determination of their microstructure, chemical composition, and surface morphology, while UV-Vis measurements were carried out in order to investigate their optical properties. Irrespective of the preparative conditions, all the films displayed the typical absorption spectrum of CdS, with an energy gap value Eg = 2.5 eV. AFM analyses showed that flat, uniform, and crack-free layers were obtained under all the adopted synthetic conditions. This result is of interest in view of potential applications in optoelectronic devices like solar cells, where a smooth and regular morphology is required. In this work, XPS analyses of a representative CdS thin film deposited at 400 °C are presented. Besides the wide scan spectrum, charge corrected binding energies for the Cd 3d5/2, Cd 3d3/2, Cd MNN, S 2p3/2, S 2p1/2, O ls, and C 1s surface photoelectron signals are reported and discussed.