Date on Master's Thesis/Doctoral Dissertation

12-2025

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Physics and Astronomy

Degree Program

Physics, PhD

Committee Chair

Sumanasekera, Gamini

Committee Member

Yu, Ming

Committee Member

Mendes, Sergio

Committee Member

Jasinski, Jacek

Committee Member

Satyavolu, Jagannadh

Author's Keywords

Plasma; graphene; carbon; nanotube; catalyst; plastics

Abstract

This research leveraged incorporation of capacitively coupled radio frequency plasma into chemical vapor deposition (CVD) for a reduction in the temperature requirements [a reduction of energy barrier] needed for the conversion of methane (CH4), carbon dioxide (CO2), and various carbon-based-waste to produce value-added carbon nanomaterials. An array of catalysts and catalyst supports were employed to optimize the synthesis of graphitic carbon under various gas environments, temperatures and pressures. The nanomaterials synthesized after fine tuning the growth parameters included graphene, carbon nanotubes (CNT), carbon microtubes and carbon nanocages with a variety of properties. Raman Spectroscopy was used as a probe to evaluate the sp2 carbon deposition without the need to transfer from the substrate which enabled versatile and non-invasive preliminary characterization. Through an analysis of the carbon peak positions and intensities, a valuable insight was gained into the quality, defects, distribution, morphology and structure of the samples. This included the presence of a split G band (G and D′) reflecting its conformal adherence to the substrate, abundance ratio of the semiconducting and metallic single-walled carbon nanotubes which compared the intensities of the G⁺ and G⁻ bands, and inspection of other peaks such as the radial breathing mode, the D band, and the 2D band. Further investigation of the nanomaterials was conducted with Scanning Electron Microscopy and Transmission Electron Microscopy. In summary, thermal and plasma enhanced CVD of CH4 was optimized for synthesis of valuable carbon materials v which then enabled three applications: improved electrocatalytic activity of Fe@CNC, improved anode performance of Si@graphene in Li-ion batteries, and in-situ CNT growth on lunar regolith simulants for improved properties of geopolymerization. CO2 conversion was achieved via bubbling in liquid metal catalysts and through a two stage methanation reaction, both of which enabled us to extract graphene. PECVD on carbon-based-waste also enabled synthesis of valuable carbon material warranting further investigation into plasma for scalable applications using waste products.

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