Synthesis and shape control of functionalized cadmium telluride nanoparticles

Abstract

The synthesis of organically and water soluble cadmium telluride nanoparticles by a facile hybrid solution high temperature method is presented. This method involves the reaction by the addition of an aqueous suspension or solution of a cadmium salt (chloride, acetate, nitrate or carbonate) to a freshly prepared NaHTe solution. The nanoparticles were prepared by passivating with organic surfactants such as hexadecylamine (HDA) and tri-n-octylphosphine oxide (TOPO) for their solubility and stability in organic solvents. To stabilize and make the nanoparticles water soluble, L-cysteine ethyl ester hydrochloride and triethanolamine were used as capping agents. The absorption and photoluminescence spectroscopy, fourier transform infrared spectroscopy, powder X-ray diffraction, transmission electron microscopy and high resolution transmission electron microscopy techniques were used to confirm the quality of the as-synthesized nanoparticles. All measurements were performed without any post preparative size separation of the nanoparticles. The dissertation comprises of four chapters. The first chapter is a brief description of the properties of nanomaterials and a literature review on some of the principal routes to synthesize nanomaterials. The mechanisms of particle growth and shape control are also discussed. Finally some key applications of CdTe are described. The second chapter deals with the synthesis of HDA and TOPO-capped CdTe nanoparticles. The reaction parameters such as reaction time, reduction time of tellurium, Cd:Te ratio, reaction temperature and cadmium source were varied to investigate their influence on the optical properties and morphology of the particles. Details of the absorption features such as excitonic peaks and band edges are presented. The emission properties are also discussed. The morphology of the particles was investigated by electron microscopy and powder X-ray diffraction techniques. It was found that the cadmium source (chloride, carbonate, acetate and nitrate) had a profound effect on the final morphology of the particles. A detailed mechanism for the particle growth is presented. The synthesis of cysteine and TEA-capped CdTe nanoparticles are described in Chapter three. A systematic study of the effects of the capping group, pH, reaction time and cadmium source was carried out for the water soluble CdTe nanoparticles. The absorption and emission data for the particles are discussed in detail. The electron microscopy images confirm the nanosize and crystalline nature of the particles. In addition fourier transform infrared spectroscopy was used to confirm the capping of the particles by cysteine and TEA. All the cadmium sources were found to be successful in producing high quality water soluble CdTe particles. The final chapter four is a summary of general conclusions of the study.