Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (M.S.)--Marshall University, 2002. / Title from document title page. Document formatted into pages; contains 136 p. Includes vita. Includes bibliographical references (p. 60-64).

Thesis (M.Med.Sc.)--University of Hong Kong, 2009. / Includes bibliographical references (p. 53-56).

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 163-179).

The exponential expansion in the field of biophotonics over the past half-century has been leading to ubiquitous basic science investigations, ranging from single cell to brain networking analysis. There is also one biophotonics technology used in clinic, which is optical coherence tomography, mostly for high-speed and high-resolution endoscopy. To keep up such momentum, new biophotonics technologies should be aiming at improving either the spatial resolution or temporal resolution of optical imaging. To this end, this thesis will address a new imaging technique which has an ultra-high temporal resolution. The applications and its cost-effective implementations will also be encompassed. In the first part, I will introduce an entirely new optical imaging modality coined as optical time-stretch microscopy. This technology allows ultra-fast real-time imaging capability with an unprecedented line-scan rate (~10 million frames per second). This ultrafast microscope is renowned as the world’s fastest camera. However, this imaging system is previously not specially designed for biophotonics applications. Through the endeavors of our group, we are able to demonstrate this optical time-stretch microscopy for biomedical applications with less biomolecules absorption and higher diffraction limited resolution (<2 μm). This ultrafast imaging technique is particularly useful for high-throughput and high-accuracy cells/drugs screening applications, such as imaging flow cytometry and emulsion encapsulated drugs imaging. In the second part, two cost-effective approaches for implementing optical time-stretch confocal microscopy are discussed in details. We experimentally demonstrate that even if we employ the two cost-effective approaches simultaneously, the images share comparable image quality to that of captured by costly specialty 1μm fiber and high-speed ( >16 GHz bandwidth) digitizer. In other words, the cost is drastically reduced while we can preserve similar image quality. At the end, I will be wrapping up my thesis by concluding all my work done and forecasting the future challenges concerning the development of optical time-stretch microscopy. In particular, three different research directions are discussed. / published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

The goal of renewable solar energy research is to develop low-cost, high-efficiency photovoltaic technologies. However, with the growing deployment of solar cells, approaching the terawatt scale, absorber materials reliant upon rare or unfriendly elements become a crucial issue. Thus, the primary objective of this dissertation is the development of a low-cost fabrication method for (i) thin-film solar cells and (ii) dye-sensitized solar cells using earth-abundant materials. In thin-film solar cells, the kesterite Cu₂ZnSnS₄ with earth abundant elements is used as an absorber layer. It possesses a high absorption coefficient, direct band gap, and good long-term stability compared to the traditional CdTe and Cu(In,Ga)(S,Se)₂ (CIGS) absorber layers. A facile hot-injection approach for synthesizing Cu₂ZnSn(S,Se)₄ nanocrystals with varied Se to (S+Se) ratio is developed to systematically investigate the role of Se in Cu₂ZnSn(S,Se)₄ nanocrystals and the evolution of Cu₂ZnSn(S,Se)₄ nanocrystals to Cu₂ZnSn(S,Se)₄ film during the sulfurization step to address the problems associated with its narrow compositional window and the loss of Sn during heat treatment. Additionally, the existing substrate-type device configuration for these solar cells uses a molybdenum (Mo) back contact, which suffers from serious disadvantages like the (i) presence of a Schottky barrier at the Mo/Cu₂ZnSn(S,Se)₄ interface and (ii) decomposition of Cu₂ZnSn(S,Se)₄ at the Mo interface. Accordingly, a low-cost and Mo-free superstrate-type device configuration of Au/Cu₂ZnSn(S,Se)₄/CdS/TiO₂/ITO/glass is developed to evaluate the conversion efficiency and to avoid the occurrence of a Schottky barrier at the interface and potential decomposition pathways induced by the formation of Mo(S,Se)₂. Furthermore, with the addition of ethyl cellulose, the loss of Sn associated with the conversion of CZTSe to CZTSSe during the grain growth process is mitigated, leading to an increase in the conversion efficiency compared to that of the precursor film without using ethyl cellulose. Such an improvement can provide insight into the grain growth of CZTSSe during the sulfurization process and thereby enhance the feasibility of sustainable, high efficiency CZTSSe solar devices. The excellent characteristics of dye-sensitized solar cells (DSSCs) with short energy-payback time, simple assembly, and eco-friendly features make them a potential option to utilize solar energy. Accordingly, a facile, low-cost, template-free route for TiO₂ hollow submicrospheres embedded with SnO₂ nanobeans is developed for use as a versatile scattering layer in DSSCs. Our designed structure simultaneously promotes dye adsorption, light harvesting, and electron transport, leading to a 28 % improvement in the conversion efficiency as compared with the film-based SnO₂. In addition, a naturally-derived carbonaceous material as a Pt-free counter electrode for DSSCs is also developed for the first time: carbonized sucrose-coated eggshell membrane (CSEM). It is found that the carbonized sucrose-coated eggshell membranes consist of unique micropores of less than 2 nm, which effectively catalyze the triiodide into iodide in the light-electricity conversion process, leading to an improvement in the V [subscript oc] and a competitive efficiency as compared to that of a DSSC with a traditional Pt-based counter electrode. / text

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