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Optical sensing techniques have the capability of capturing large amounts of information across the sensing field, thus they have been broadly used in many areas. Some of the traditional optical sensing tools, for example microscopes, have been built and used over a century and are still essential in many applications such as biomedical research and clinical diagnosis. However, these traditional optical sensing devices are usually large-scale, heavy-duty and expensive instruments, which also require skilled expertise to operate. Therefore, traditional optical sensing devices are often limited in specialized research facilities and not easily accessible to the general public. To meet the emerging demands of applying optical sensing more frequently in people’s daily life, more compact and inexpensive devices are required.A portable optical sensing platform based on smartphones has been developed, on top of which several advanced optical sensing techniques can be implemented. To be specific, the basis of the platform is a smartphone-based microscopic system with decent resolution in a sufficient field-of-view. With minimum optical elements attached to the platform, the system can be easily adapted into more advanced optical sensing tools, targeting much more optical information far beyond just intensities. For instance, the platform is equipped with a portable polarizer to become an imaging polarimetry, which is sensitive to the surface feature and roughness of the imaging sample. The platform is also integrated with a specially designed micro-grating to be implemented as a miniature wavefront sensor, which can be utilized to detect the phase information. The technique is based on one of the efficient quantitative phase imaging methods called wavefront curvature sensing, which uses two out-of-focus images of the pupil generated simultaneously to calculate the phase. Moreover, the detected phase information can be further produced into a height map across the field-of-view, yielding 3D tomography of the sensing sample. The technique is demonstrated with imaging laser generated wavefronts as well as other bio-specimen, such as human red blood cells.

Abstract: As one of the most commonly applied semiconductors, nanostructured silicon has received considerable attention over the past several decades due to its suitable band gap for light harvesting (1.2 eV for bulk crystal and up to 1.9 eV for nanocrystals), unique tunable photoluminescence (PL) and high biocompatibility and low toxicity. Significant effort has been made to fabricate and optimize silicon nanocrystal (SiNC) based devices. However, numerous important fundamental questions still remain. Therefore, this thesis mainly focuses on the elucidation of several fundamental research topics in the SiNC area, including nanocrystalline morphology control and evolution, surface functionalization and corresponding optical response of SiNCs, as well as the synthesis of particle/polymer hybrid materials. The thesis starts with an introduction about physical and chemical properties of SiNCs, general synthetic approaches, the present strategies of morphology control, as well as numerous surface modification approaches. Then details of a convenient method for preparing alkyl-functionalized silicon nanocubes are provided in Chapter Two with discussions about the mechanism of the particle size and shape control. Chapter Three focuses on the “one-pot” synthesis of homogenous SiNC/polystyrene hybrid materials. Also, three prototype micro/nano structures were fabricated for the demonstration of the utility of material hybrid characteristics such as bright photoluminescence (PL), high solvent processability and chemical stability. In Chapter Four, surface functionalization of SiNCs via thermally induced hydrosilylation is reexamined. The successful ligand functionalization processed at various temperatures under air atmosphere and the formation of ligand oligomers on SiNCs were noticed. These strongly suggest that an alternative mechanism exists to promote low temperature thermal hydrosilyaltion as well as ligand oligomerization on SiNCs. The potential influence of surface oxide species on SiNC optical properties is further described in Chapter Five. Based on a systematic study, it is clear that the surface defects or traps created by suboxides are strongly relevant to the non-phonon assisted nanosecond PL lifetime decay found from yellow/orange emitting ligand-functionalized SiNCs. Finally, Chapter Six presents the conclusions of each chapter and some recommended future work relative to SiNC science.