Browsing by Subject "core-shell"

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    Heterostructured Quantum Dots from Nonthermal Plasmas
    (2019-07) Hunter, Katharine
    This work investigates the production and properties of heterostructured quantum dots (QDs) composed of a group IV semiconductor and an inorganic shell. A nonthermal plasma process for the growth of heterostructured QDs has been developed. The design of this process leverages pioneering work from Mangolini et al. for the nonthermal plasma growth of silicon QDs. The use of plasmas has emerged as a leading technique for the synthesis of group IV NCs because of the unique set of advantages which set this approach apart from other gas-phase approaches. Plasma properties, specifically the temperature and density of neutral and charged species (electrons and ions), dictate the reactive environment within which QDs are shaped. Furthermore, these advantages extend to the growth of core/shell NCs and allow the processing of heterostructured QDs inaccessible by conventional solution-phase processing. First, this work explores germanium (Ge) QDs with silicon (Si) shells deposited epitaxially. This simple QD heterostructure provides crucial insight into the development of a nonthermal plasma process for the synthesis core/shell structures. Furthermore, the epitaxial Ge/Si system allowed for the exploration of strain manipulation of semiconductor bandstructures in core/shell QDs. This strain engineering was extended to germanium (Ge) - tin (Sn) QD heterostructures. This effort leverages the processes developed in for Ge/Si QD epitaxy to explore the ability to tensile strain Ge QDs and induce a direct bandgap. Next the nonthermal plasma growth of an amorphous silicon nitride a-SiNx layer on Si NC as a passivating layer was investigated. In this effort, a second process for shell growth was developed which relies on surface layer modification by plasma enhanced nitridation. Finally, we have demonstrated the application of Reverse Monte Carlo simulations to probe the structure and spatial composition of heterostructured NCs applies to the well-established system of silicon NCs doped with boron and phosphorus. Through the generation and refinement of simulated NCs based on high-energy X-ray diffraction data, elemental distribution and coordination was investigated. This approach may be of importance moving forward for the structural analysis of nanocrystalline materials with increasing compositional and structural complexity.