Date of Award

11-18-2024

Author's School

McKelvey School of Engineering

Author's Department

Energy, Environmental & Chemical Engineering

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

Nitrogen is abundant on Earth as its diatomic form, and human activity has generated a significant demand for nitrogen-containing compounds. However, its triple bond energy of 941 kJ/mol makes it a poor reactive species in the ground state. Nitrogen-containing nonequilibrium plasmas are made up of background gas, electrons, ions, and a multitude of excited states of nitrogen or even atomic nitrogen. Many of these species have rather high reactivity. As such, the plasma medium is of great potential for driving chemical reactions that involve nitrogen as a reactant, i.e., nitrogen fixation into compounds like ammonia, high-energy-density polynitrogen compounds, and metal-nitride materials. Contrary to the successful synthesis of many other nanocrystals, the synthesis of metal-nitride nanocrystals is underdeveloped. Plasma stands out as a promising environment for synthesizing and processing metal nitride nanocrystals such as GaN, InN, and their solid solution, which are of interest for optoelectronic and power electronics applications. In this dissertation, the capabilities of nitrogen-containing nonequilibrium plasma are explored for the purposes of III-nitride materials synthesis and processing. First, the nonequilibrium plasma aerotaxy method was employed to synthesize GaN quantum dots and study their photonic properties. Fine size control below 10 nm diameter, the range of interest for quantum confinement, was demonstrated, and the quantum size effect was reported in spheroidal GaN nanocrystals using spectrophotometric techniques. Nanocrystal shape and size have strong influence over a material’s photonic properties. Besides small nanocrystals, nonequilibrium plasma aerotaxy was harnessed to synthesize GaN and InN nanocrystals and nanoplatelets as large as 100 nm in diameter. Secondly, a synthesis strategy for nanocrystals of the solid solution of InN and GaN (InxGa1-xN), adapted from nonequilibrium plasma aerotaxy was explored. Using thermal evaporation of a mixture of the two metals, InxGa1-xN nanocrystals that were mixed at the nanoscale constituted the end product. A strategy to control the overall composition was demonstrated, of interest for solar harvesting and light emission technologies. Finally, a plasma stabilization effect was observed in bulk GaN and InN at temperatures beyond their expected dissociation temperatures, which was used to estimate the effective chemical potential of a nitrogen-containing nonequilibrium plasma. These studies contribute additions to the library of materials accessible to nonequilibrium plasma synthesis, open an avenue for material processing using nitrogen plasma, and provide a novel perspective on the thermodynamics of the two.

Language

English (en)

Chair

Elijah Thimsen

Committee Members

Dariusz Niedzwiedzki; Peng Bai; Richard Axelbaum; Rohan Mishra; Sang-Hoon Bae

Available for download on Thursday, November 13, 2025

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