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Abstract
To date, quantum dots (QDs) have been synthesized through a number of different processes ranging from colloidal synthesis to electrochemical methods to chemical vapour deposition (CVD). This thesis focuses on the synthesis of high-quality CdSe nanocrystals through a bench- top colloidal synthesis paying particular attention to the effects of varying the reaction temperature and reagent concentrations on the size and crystallinity of the QDs. Powder X-ray diffraction (PXRD) analysis and high-resolution transmission electron microscopy (HRTEM) highlighted a transition of the crystallite phases obtained, from cubic zinc-blende to hexagonal wurtzite and back again to the cubic phase as a function of reaction time. The nature of this phase shift is believed to be due to the rapid growth along the {111} crystallite facets, with the facial facets then 'catching-up', restoring the cubic symmetry. Due to the presence of many NMR active species in CdSe TOP/TOPO QDs viz., 113Cd, 77Se, 13C, 31P, 77S and 1H solid-state nuclear magnetic resonance spectroscopy (SS-NMR) was used to investigate the interaction of the organic capping agent and the QD core.
High-quality TOP/TOPO capped CdSe QDs displaying a narrow emission band were then grafted onto graphene nanosheets through a simple wet chemical procedure. A significant red- shift of both the broad absorption and narrow emission spectra of the QDs was observed upon attachment to graphene, as determined by UV-vis absorption and photoluminescence spectroscopy, whilst HRTEM data clearly shows the successful decoration of CdSe QDs on the graphene sheets. This type of nanocomposite may have potential applications in the fields of optics, biological imaging and sensing.