Towards understanding the nanomaterials characteristics of vapor transported CdS in an open end tube

Abstract

In this study, the evaporation condensation of CdS was carried out in a quartz tube with an open end. The synthesis was carried out on Au coated Si(100) and quartz substrates. The Au coated Si and quartz substrates were put approximately 1 cm and up to 25 cm away from the alumina boat. It was observed that the materials deposited on the substrates in the reactor tube formed with different colors in different regions. The regions were found to be 6–14 cm, 14–18 cm and 18–24 cm away from the center of the alumina boat and were labeled B, C and D, respectively. The morphology, structural and chemical composition of the obtained materials at different regions were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive analysis of X-ray (EDAX), respectively. EDAX analysis revealed the presence of Cd and S with nearly stoichiometric CdS at region B. At region C a pronounced peak of oxygen was observed together with the peaks of Cd and S. At region D the S peak was diminished. XRD examinations revealed the formation of single crystalline phase of hexagonal CdS in region B. Mixed crystalline phases of hexagonal CdS, monoclinic cadmium sulfite, CdSO3, and cubic CdO were formed in region C. Cubic CdO was formed in region D. The SEM examinations showed that the morphology of CdS was nanowires (NWs) in shape. The morphology of the mixed oxysulfide phase was a mixture between NWs and nanoparticles (NPs). The morphology of CdO was NPs in shape. The optical constants, the thickness and the surface roughness of the prepared nanostructured films were determined by spectroscopic ellipsometry measurements. A model consisted of two layers was used to fit the calculated data to the experimental ellipsometric spectra. The obtained optical constants were compared with those of CdS and CdO obtained by other preparation methods.