Far-infrared investigations of the surface modes in CdS thin films

The properties of Cadmium sulphide (CdS) thin films were investigated by applying atomic force microscopy (AFM) and far–infrared spectroscopy. CdS thin films were prepared using thermal evaporation technique under a base pressure of 2 × 10−5 torr. The quality of these films was investigated by AFM spectroscopy. We apply far–infrared spectroscopy to investigate the optical properties of CdS thin films, and reveal the existence of a surface optical phonon (SOP) mode at 297 cm−1. For the first time, the dielectric function of CdS thin film is modeled as a mixture of homogenous spherical inclusions in air by the Maxwell–Garnet formula. In the analysis of the far–infrared reflection spectra, a numerical model for calculating the reflectivity coefficient for a system which includes films and substrates has been applied.