Welch, JO; (2014) Nanodiamonds: From biology to engineering. Doctoral thesis , UCL (University College London).

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Text Joseph Orin Welch Thesis corrections 29 may.pdf Download (30MB) | Preview

Abstract

Whilst diamond nanoparticles have been synthesised by the detonation method since the middle of the 20th century, it was not until the development of their fully dispersed form in 2008 that the hugely varied array of potential applications opened up. These prospective uses are described in chapter 2, spanning the breadth of the sciences; from the chemical (ion sensors and electrochemical electrodes), the biological (drug delivery and intracellular monitoring), to the physical (composite materials and growth nucleation seeds). Highlighting this versatility, chapter 5 of this thesis covers the use of ND as a neuronal biomaterial, investigating for the first time the role of the size, production method and surface functionalisation on neurite extension, where it was found that the only significant variable was the size of the ND used, suggesting the curvature of particle is of high importance. A patterned ND surface was also fabricated and this resulted in the successful growth of neuronal networks along the ND patterning, down to ND track widths of 10 μm. Chapter 6 presents a study into the electrical characteristics of nanodiamond. Here for the first time, ND layers with various surface terminations were produced and verified using Fourier transform infrared spectroscopy. These layers were then probed using impedance spectroscopy to obtain modelled values of the layers’ resistance and capacitance as a function of measurement temperature. This data was manipulated into Arrhenius plots to extract activation energies of the observed conduction paths. The hydrogen terminated ND layers were shown for the first time to be stable for short heating durations up to 475°C, although longer heating duration at this temperature did cause permanent damage to the ND layer. Oxygen terminated ND was found to be less stable when heated in atmospheric conditions, with permanent degradation occurring at 200°C. However when measured in vacuum, these layers showed resilience similar to that seen on the hydrogen terminated ND, suggesting the hydrogen termination is providing protection against oxidative degradation in atmospheric conditions. The next chapter documents the attempts to fabricate thin, conformal layers of ND within the channels of a microchannel plate (MCP) – the electron amplification stage of a night vision device. This work resulted in the first successful seeding of ND throughout the first 60 μm of the MCP channel, as requested by the industrial sponsor of this work, Photonis. This chapter also presents the iterative designs of a custom cooler and sample mount for the microwave plasma enhanced chemical vapour deposition chamber used for low temperature diamond growth both in this chapter and the final experimental chapter. The last experimental chapter details a novel investigation into the optimal conditions for ND to be grown into a thin film for use as a secondary electron emitter. The results presented include Raman spectroscopy (for film quality assessment), scanning electron micrographs (to provide topographical information), atomic force microscope line scans (to estimate film thickness) and finally secondary electron yield experiments upon each of the films. It was found that the films grown with the highest applied microwave power -­‐ resulting from the most aggressive cooling -­‐ gave the highest secondary electron emission yield, slightly under 10 (meeting the objective set by Photonis) along with a sharper sp3 peak at 1333cm-­‐1.

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