Synthesis and study of organically capped ultra small clusters of cadmium sulphide

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Ultra small clusters of cadmium sulphide are synthesized using non-aqueous and aqueous chemical methods. Thiophenol has been used as a capping agent for non-aqueous synthesis whereas various reagents such as mercaptoethanol, hexametaphosphate, ethylene glycol and ethanol have been 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 spectroscopy. Particles as small as ∼0.7 nm diameter could be synthesized with thiophenol and mercaptoethanol as additives. The effect of varying the molarities of the different additives on the properties of the CdS nanoclusters synthesized are discussed. Systematic ageing studies of the nanoclusters showed that larger particles age faster than the smaller clusters. Ageing also leads to better crystallization of the particles. It has been observed that the smallest particles (∼0.7 nm diameter) possess tetrahedrally bonded fragments of CdS and intercluster structural long range order does not exist. However, bigger particles (∼2.0 nm diameter) show bulk cubic structure. X-ray photoelectron spectroscopy studies have been done to study the purity and stoichiometry of the clusters synthesized and strongly support the existing proposal of the formation and stability of CdS nanoclusters.

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