Investigation of Microsphere Convective Deposition for Photonic and Biological Applications

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CBET-0828426GilchristThe proposed research will generate a fundamental description of the physics involved in the deposition of a monolayer of particles using convective self-assembly. Drawing an evaporating meniscus across a substrate, a process related to the "coffee ring effect" and the Langmuir-Blodgett technique, forms a structure of particles ranging from random and ordered sub-monolayer to well-ordered multilayers. Although many recently developed processes take advantage of this technique, primary questions remain regarding the fundamental physics involved with particle convection and self-assembly. In situ investigation of monolayer deposition will be performed using high speed confocal laser scanning microscopy. Preliminary results suggest many parameters not previously considered affect deposition and various mechanisms generate microsphere pre-alignment in the thin film prior to deposition. Experiments that incorporate processing, suspension, and substrate conditions not previously explored will be used to develop a model to shed light onto the mechanisms that link the controllable macroscopic properties to the microstructure. Fabrication of colloidal monolayers will be used directly in two specific applications. Performance of InGaN light emitting diodes (LEDs) is inhibited by the index mismatch of the GaN/air interface. The proposed process will be used to fabricate microlens arrays where the microstructure determines the light extraction efficiency. Preliminary results demonstrate increased light output power by 219%. In a parallel effort, design of monolayer arrays labeled with antibodies for whole blood detection of CD4+ lymphocytes will enable enhanced screening for HIV/AIDS. The microstructure of these deposited monolayers will dictate the capture efficiency and proliferation of target cells and enable release of these cells for analysis. Broader Impacts: Although colloidal convective deposition is used in many technologies, the fundamental physics is poorly understood. This research will develop a predictive model based on observations obtained from direct 3D particle tracking during deposition for various surface and suspension properties. Through this research, the importance of controlling this microstructure will be demonstrated in two applications that have significant potential impact on their respective industries. First, the microlens arrays fabricated using this technique have the potential to surmount the current state-of-the-art LED photon extraction, allows scale-up for industrial applications, and is low-cost as compared to current techniques of surface patterning via electron beam lithography. In whole blood analysis, this technique can be generalized for a variety detection schemes and will aid development of a process that aims to bring low cost detection to regions lacking proper medical resources. This work will directly provide both graduate and undergraduate educational opportunities in an area at the convergence of several technologically-critical research areas including microfluidics, suspension transport, photonics, and bioengineering.