Understanding plasma nucleation for a priori control of synthesis of carbon allotropes at the nanoscale

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1335990SankaranCarbon nanomaterials are a special class of materials with a diverse range of structures and unparalleled electronic, photonic, and chemical properties that have elicited interest for a wide-range of technological applications. This project will study the homogeneous nucleation of carbon nanomaterials in a novel microplasma process. Microplasmas are non-equilibrium, atmospheric-pressure plasmas formed in confined electrode geometries that allow particles to be nucleated and rapidly quenched to limit their final size and agglomeration. Preliminary results have shown that nanodiamond, carbon clusters less than 5 nm in size exhibiting diamond phase, can be produced at near ambient conditions, far from the thermodynamic stability of diamond, by dissociation of ethanol vapor in a microplasma. This project will extend these experiments to the formation of other carbon allotropes including fullerene and graphene. Dissociation of carbon precursors in the microplasma with varying C:H:O ratios will be characterized by optical emission spectroscopy to relate radical species such as carbon dimers and atomic hydrogen to particle nucleation. Particle nucleation will be monitored in real time by aerosol mobility measurements. The as-grown carbon nanomaterials will be collected and further characterized by high-resolution transmission electron microscopy, micro Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. A particularly important aspect of the work will be to explore the influence of quenching rate on particle formation by pulsing the microplasma at different frequencies.This project will provide new insight into the formation of carbon nanomaterials. By linking plasma chemistry to material structure, an empirical model for homogeneous nucleation analogous to chemical vapor deposition (CVD) of thin films will be developed. Size-structure relationships such as the stability of nanodiamond will be established by varying the residence time and quench rate in the microplasma. Ultimately, the research will enable the structure of carbon nanomaterials to be controlled at nucleation so that it is possible to tune their properties for various applications. The research activities will provide educational opportunities for graduate, undergraduate, and high school students, and be a part of an elective course on nanotechnology at a local high school.