Reaction/Transport Behavior in the Synthesis of Functionally-Encoded Nanowires via the Geode Process

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The proposed project will investigate the chemical reactions and transport of chemical species involved in the synthesis of semiconductor nanowires on the interior surface of hollow, porous-walled microspheres. The use of these microspheres as nanowire growth substrates -- the "Geode process" -- promises to be a new platform for the scalable manufacturing of functional semiconductor nanowires for a range of applications (e.g., thermoelectrics, optical coatings, large-area electronics, etc.). In the Geode process, hollow microspheres provide efficient gas transport and a large internal surface area for nanowire growth while preventing agglomeration and protecting the delicate liquid droplet that choreographs nanowire growth. The overarching objective of the proposed research is to gain a fundamental understanding of the underlying kinetics and transport phenomena to enable precise control of nanowire synthesis. The proposed collaboration between researchers from Georgia Tech and ALD NanoSolutions, Inc., has the potential of producing transformative results and enabling future commercial exploitation of this technology.A novel experimental methodology will be employed. The specific objectives of the work are three-fold: (1) study the growth rate in steady state experiments as function of reaction conditions to quantify any mass and heat transfer limitations and optimize microsphere structure to mitigate adverse impacts on nanowire quality; (2) perform transient experiments that focus on detailed quantification of dopant concentration profiles in the nanowires when precursor gas mixtures are modulated; and (3) preliminarily quantify transport properties in a pilot-scale fluidized bed reactor to bridge the gap between lab-scale synthesis and scalable reactor technology. In addition to training graduate students the research team plans to engage in societal and educational outreach via the Nanovation podcast, by including material related to nanomaterials in their undergraduate courses, and by developing a new hands-on fluidized bed activity for classroom use and K-12 outreach. These activities will highlight the potential of large scale nanomanufacturing and fluidized bed reactor technology specifically for advanced materials and device processing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.