NIRT: Multiscale Modeling of Nanowire Growth - From Atoms to Wires

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This proposal was received in response to Nanoscale Science and Engineering initiative, NSF 04-043, category NIRT. The objective of this research is to develop and test theories describing the vapor-liquid-solid (VLS) approach to nanowire growth. Comprehensive investigations of the mechanisms and processes that govern nanowire growth by the VLS method will be carried out within the framework of a multiscale-modeling approach, closely coupled with experimental synthesis and characterization efforts providing the framework for validation of the theoretical models. The research will address outstanding issues in VLS nanowire growth that are relevant to the realization of nanowire device technology, specifically: (i) the factors controlling growth rate and growth direction of the wire, (ii) the mechanisms underlying the formation of complex branched and coiled nanowire morphologies, and (iii) factors controlling compositional abruptness in the synthesis of compositionally modulated semiconductor nanowires. The research will be based on the application of an integrated combination of modern methods of applied mathematics, numerical analysis, and atomistic simulations, in close collaboration with controlled synthesis and advanced characterization experiments.One-dimensional semiconductor nanowires are being considered for numerous technological applications, including high-performance transistor logic, ultra-sensitive single molecule biosensors, nanoscale diodes and lasers, and hierarchically integrated devices/interconnects. The realization of these technologies requires precise control of the novel properties that arise from variations in nanowire diameter, morphology, composition, and internal interfaces. If successful, this effort will lead to the development of validated predictive models for designing optimal processing conditions to produce VLS grown nanowires with desired properties. The theoretical research is closely related to a broad class of mesoscopic phenomena that control materials synthesis and phase transformations at the nanoscale. Thus it is expected that the theoretical methods and modeling tools developed within this research will be useful to researchers working in these areas.