SYNTHESIS AND STUDY OF ORGANICALLY CAPPED ULTRA-SMALL CLUSTERS OF CADMIUM-SULFIDE

Ultra small clusters of cadmium sulphide are synthesized using non-aqu eous and aqueous chemical methods. Thiophenol has been used as a cappi ng agent for non-aqueous synthesis whereas various reagents such as me rcaptoethanol, hexametaphosphate, ethylene glycol and ethanol have bee n used as additives for an aqueous method of synthesis. Properties of the clusters synthesized are discussed based on optical absorption, X- ray diffraction, transmission electron diffraction and photoelectron s pectroscopy. Particles as small as similar to 0.7 nm diameter could be synthesized with thiophenol and mercaptoethanol as additives. The eff ect of varying the molarities of the different additives on the proper ties of the CdS nanoclusters synthesized are discussed. Systematic age ing studies of the nanoclusters showed that larger particles age faste r than the smaller clusters. Ageing also leads to better crystallizati on of the particles. It has been observed that the smallest particles (similar to 0.7 nm diameter) possess tetrahedrally bonded fragments of CdS and intercluster structural long range order does not exist. Howe ver, bigger particles (similar to 2.0 nm diameter) show bulk cubic str ucture. X-ray photoelectron spectroscopy studies have been done to stu dy the purity and stoichiometry of the clusters synthesized and strong ly support the existing proposal of the formation and stability of CdS nanoclusters.