Electrodeposition is a novel method for fabrication of diamond-like carbon (DLC) films on metal substrates. In this work, DLC was electrochemically deposited on different substrates based on an anodic oxidation cyclization of acetylene in liquid ammonia. Successfully anodic deposition was carried out for DLC onto nickel substrate at temperatures below -40°C. Comparative studies were performed on a series of different carbon sources (acetylene, sodium acetylide, and a mixture of acetylene and sodium acetylide). The films were characterized using a variety of methods including Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), XPS valence band spectra, and/or scanning electron microscopy (SEM). Raman spectroscopy is used as a bench mark technique to verify the presence of deposited DLC films, to access the films homogeneities, and to provide the ratio of the different carbon phases, mainly disordered graphite (D) and graphite (G) phases in the films. A combination of the Raman with FTIR and valence band spectra analysis allowed the distinction between hydrogenated DLC and unhydrogenated DLC films. Three different kinds of DLC [(1) hydrogenated DLC (a-C:H); (2) tetrahedral hydrogenated DLC (ta-C:H); and (3) graphitic-like DLC] were deposited depending upon the deposition conditions and substrates. Temperature and current density are the most important parameters to govern the quality of the deposited films, where adding of acetylide into the electrolyte led to films with a higher degree of graphitic phases. The proposed mechanism for acetylene anodic oxidation does not involve direct electron transfer but electrochemical cyclization of acetylene radical cations and hydrogen abstraction at the termination steps. Sodium acetylide, however, dissociates to an acetylenic ion, C2H-, in liquid ammonia. The electrochemistry heterogeneity also leads to island and two-dimensional (2D) nucleation growth of DLC films. Different bond formations of metal to carbon and different chemisorptions of acetylene on metal play important roles in governing the film properties. Using mixed C2HNa and C2H2 as electrolyte, polycrystalline diamond and hexagonal diamond are formed on Mo and stainless steel, respectively. This is the first time to report that polycrystalline diamond can be grown electrochemically at temperature below -40ºC. The preliminary studies on substrate pretreatment with diamond powder and SiC 600 are studied. The effect of the substrate on the film quality for the electrodeposited DLC films described herein is similar to that for diamond deposition via chemical vapor deposition (CVD).
| Identifer | oai:union.ndltd.org:unt.edu/info:ark/67531/metadc4580 |
| Date | 08 1900 |
| Creators | Pingsuthiwong, Charoendee |
| Contributors | Golden, Teresa D., Chyan, Oliver M. R., Omary, Mohammad, Pérez, José M. |
| Publisher | University of North Texas |
| Source Sets | University of North Texas |
| Language | English |
| Detected Language | English |
| Type | Thesis or Dissertation |
| Format | Text |
| Rights | Public, Copyright, Pingsuthiwong, Charoendee, Copyright is held by the author, unless otherwise noted. All rights reserved. |
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