Title:

Advances in Silicon Nanocrystals

Author: Qian, Chenxi
Department: Chemistry
Issue Date: Jun-2017
Abstract (summary): Silicon nanocrystals (ncSi), which are considered as greener alternatives to traditional nanocrystals like CdSe and PbS, offer the benefits of being earth abundant, potentially inexpensive, purportedly less toxic and compatible with silicon electronics. The work presented in this thesis focuses on the contributions in the advances in silicon nanocrystals. This would include developing new synthesis methods for ncSi with simpler precursors and higher yields, exploring new design strategies to enhance the stability and photoluminescence (PL) absolute quantum yield (AQY) of the ncSi, and probing other surface reactions, such as the reduction of gaseous carbon dioxide by the nanosilicon surface hydrides (ncSi:H). Specifically, a batch synthesis based on the thermal solid-state disproportionation of SiO was developed. We managed to pinpoint an optimal temperature range of 850-1100 â , in which the nucleation and growth of ncSi in a SiO2 matrix were observed. More importantly, by implementing this synthetic route, we were able to prepare ncSi with a wider size range and observe directly the size-dependent PL AQY of these ncSi. For the first time we observed optically the both upper and lower critical size at which the quantum size effects (QSE) begin to switch on and switch off, respectively. Apart from this, a major step was taken towards the synthesis of a more stable ncSi ensemble against oxidation by capping the surface with perfluorocarbon chains. Lower rates of oxide shell forming on the ncSi surface was observed and a higher PL AQY was measured for these ensembles. On the other hand, by utilizing the reducing ability of the ncSi surface hydrides, we were able to convert gaseous CO2 selectively to CO, and the observation was unprecedented. The work presented in this thesis has pushed the boundaries of ncSi research, towards a more thorough understanding in the fundamentals and surface chemistry of ncSi.
Content Type: Thesis

Permanent link

https://hdl.handle.net/1807/79421

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