Pulsed-DC plasma-assisted CVD
: construction, plasma analysis, diamond growth, and possible alternative in nanocomposite

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Research is presented for expanding the capabilities of a pulsed-DC PA-CVD reactor and increased understanding of diamond growth parameters within. Expanding operational capabilities involved upgrades to the electrode and cooling set up through several iterations. The original design was replaced with smaller electrodes and improved cooling, allowing for higher power inputs and more reliable and stable plasma production. This resulted in long, stable growths producing high-quality diamond films. Each upgrade to the electrode design required operational Taguchi optimization in order to understand the new limitations as well as increase understanding of parameter influence on the grown diamond. The final design incorporated novel asymmetric electrode cooling and a gas/water cooled cathode. The improved plasma stability allowed for spectral plasma analysis, providing insight to Hβ and C2* radical distribution and primary plasma reaction pathways. Spectral and growth analysis of closed chamber, zero gas flow growth was also explored, a first with this type of instrument. Diamond quality does not appear to be affected by the closed chamber growth, but plasma stability severely limited extended testing. With a new, cooler anode/substrate complex, low melting point substrate growth was trialled. Silicon growth produced limited success, reflecting the recent literature's limited discussion of the material, but a novel copper substrate produced rapid growth of free-standing high-quality diamond films. The production of these films produced interest in the exploration of diamond/epoxy nanocomposites. DND and HPHT diamond powder nanocomposites were manufactured and mechanically tested for a variety of physical properties. The HPHT nanocomposites showed similar moduli to the DND equivalent with less reduction in failure strain or UTS. Overall, this showcased promising variations between materials that could be used for future applications.
Date of Award2 Dec 2021
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorFabrizio Scarpa (Supervisor), Neil A Fox (Supervisor) & Thomas Bligh Scott (Supervisor)

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