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UBC Theses and Dissertations
Microfluidic and terahertz technologies for integrated spectroscopic systems Collier, Christopher Michael
The terahertz (THz) spectrum, being approximately 0.1-10 THz, is the region of the electromagnetic spectrum that lies beyond the reach of electronic and optical devices. Because of this unique spectral region, THz radiation has found its place in many contemporary applications. In particular, THz radiation has been used in biochemical analyses, via THz spectroscopy. Terahertz spectroscopy is sensitive to vibrational and rotational modes of organic species, and this functionality can be enhanced by integrating THz spectroscopy within lab-on-a-chip platforms. Such platforms can enable high-sensitivity and rapid interrogation of biochemical species via THz spectroscopy. However, the integration of THz spectroscopy in lab-on-a-chip platforms has not yet been achieved. This is due to unresolved (and fundamental) challenges on the underlying structures and materials being used for microfluidic actuation and THz emission. This thesis addresses these challenges through enhancements towards a digital-microfluidic- (DMF)-based THz-time-domain-spectroscopy (TDS) system. For microfluidic actuation, this work focuses on the development of DMF structures having practical addressability and microfluidic actuation with independent two-dimensional control. Three such structures, the square electrode, cross-referenced, and multiplexer grid, are explored. It is found that the multiplexer grid is the only DMF structure that provides practical addressability and independent two-dimensional control. For THz emission, a variety of photoconductive materials are investigated to realize effective THz emission with minimal Joule heating flux. This is a key point for the integration of THz spectroscopy within lab-on-a-chip platforms, as it becomes necessary to avoid evaporation of the biochemical species. Materials exhibiting transient mobility (such as GaP) and surface-enhanced recombination (such as semiconductor nanocomposites and textured InP) are explored. It is found that photoconductive THz emitters made with textured InP materials provide similar THz emission characteristics to their bulk counterparts but have an order of magnitude lower Joule heating flux. Terahertz spectroscopy is ultimately performed on a variety of vapour, liquid, and solid samples to develop and test the THz spectroscopy analysis method, to propose dimensions and THz-compatible-materials for the DMF-based THz-TDS system, and to demonstrate THz-TDS on biochemical species. The findings of this work lay the groundwork for the development of future DMF-based THz-TDS systems.
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