Colloidal synthesis, structural characterisation and single molecule spectroscopy of semiconducting nanocrystals

Fisher, Aidan Antony Edward (2018) Colloidal synthesis, structural characterisation and single molecule spectroscopy of semiconducting nanocrystals. Doctoral thesis (PhD), University of Sussex.

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This thesis will endeavour to shed new light on the photophysics of single semiconducting nanocrystals. Quantum dots, rods and other more intricate single crystals were produced through traditional hot colloidal synthesis protocols. The physical attributes of the nanoparticles (NPs) were carefully and systematically varied to evaluate a new model that describes photophysical phenomena that arise at the nanoscale. Specifically, the charge-tunnelling and self-trapping (CTST) model presented here is parameterised by a set of experimentally controllable variables which include the excitationrate, host substrate dielectric constant and the shell thickness of CdSe.CdS and CdSe.ZnS core-shell systems.

An arsenal of spectroscopic and imaging techniques were used to build a comprehensive understanding of the single NPs used for subsequent single molecule fluorescence studies. The use of the x-ray diffractometer (XRD), transmission electron microscope (TEM) and nuclear magnetic resonance (NMR) instruments have provided invaluable information on the atomic structure, crystal morphology and passivating surface ligands respectively. Single molecule studies were performed by employing an ultra-sensitive inverted optical microscope operating in total internal reflection (TIRF) mode to optimise image contrast at the coverslip surface. A bespoke automated focus module was designed and built using relatively inexpensive optics and an automated macro to permit the acquisition of data over a large temporal range. This was especially important for the generation of meaningful blinking data that was subsequently analysed and compared to simulated blinking statistics.

Of the investigated photophysical manifestations the fluorescence intermittency, associated with single NPs, was perhaps the most thoroughly studied. The fluorescence intermittency or blinking of single NPs is characterised by the stochastic switching between emissive and non-emissive states under continuous irradiation. Typically, the blinking statistics were analysed through fitting a truncated power-law to the blinking probability density distributions (PDDs) which each consisted of at least 20000 blinking events. The gradient and characteristic exponential cut-off times were extracted and compared with data generated from CTST simulations.

The photochemistry of QDs and more recently the photo-assisted synthesis of perovskites was examined. The use of x-ray photoelectron spectroscopy (XPS) was used to support measurements performed on single NPs under relatively high laser powers to induce photoluminescence enhancement (PLE) and photoinduced blueing, which was measured using a spectral dispersion grating.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Life Sciences > Chemistry
Subjects: Q Science > QC Physics > QC0501 Electricity and magnetism > QC0522 Electricity > QC0601 Electric current (General) > QC0610.4 Electric conductivity > QC0611 Semiconductor physics > QC0611.8 Specific semiconducting substances and types, A-Z > QC0611.8.N33 Nanocrystals
Depositing User: Library Cataloguing
Date Deposited: 09 Feb 2018 12:16
Last Modified: 09 Mar 2020 14:26

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