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Fabrication and properties of diamond-like carbon films in discharge plasmas

By Maksym Rybachuk


This thesis presents theoretical and experimental study of properties of amorphous diamond-like carbon (DLC) coatings synthesised using discharge plasma methods. There were two objectives in this study. The first objective was to investigate the formation mechanism of hydrogenated DLC films (a-C:H) in an open hydrocarbon plasma source. The inductively coupled plasma (ICP) reactor was used to synthesise the films and the formation of sp2 and sp3 hybridised phases and the combination of these phases in the ICP plasma environment was studied. It was found that for a-C:H films with narrow distribution of the sp3 content the mechanical properties are determined by the degree of disorder of the sp2 fraction. The relationship between the sp3 content in fabricated films and hardness and Young's modulus was established. Raman and multi-wavelength (Vis – UV range) Raman spectroscopy was primarily used together with other suitable analytical methods to examine a-C:H films and it was found that films fabricated at higher ion energies displayed higher degree of clustering and bonding disorder than films produced at lower ion energies. All as fabricated a-C:H films were also found contain basic π-conjugated polymer inclusions as of trans-polyacetylene. The Raman results also reveal that the magnitude of Rayleigh scattered light is related to the relative density of the films, a feature that can be useful for monitoring film growth in-situ. The use of X-ray photoelectron spectroscopy (XPS) as a suitable method for measuring the sp3 content of the bulk DLC was also established. The second objective was to develop a fabrication technique that would allow fabrication of DLC films using graphite target sputtering with a single focused ion beam source and producing films with medium-high sp3 content. This research was motivated by the industrial partner of the project Laserdyne Pty Ltd that required a simple DLC deposition apparatus to be integrated into a standard, stand alone, optical thin film deposition chamber. Such technique was developed on the basis of a conventional ion beam target sputtering. In our experiments hydrogen-free DLC films with medium sp3 content were produced using a single, Kaufmann type ion source operated at low energies. The fabrication technique, denoted a reactive ion beam sputter deposition (RIBSD), was based on sputtering a graphite target at low incident angles and positioning the substrate at the grazing angles to the incoming ions, thus the incident ions (Ar and Xe ions were used) were simultaneously bombarding the target and the growing film. The effect of angle of incidence of an ion beam to the target and to the substrate in creating the sp3 content in DLC was investigated. It was found that the infringement bombardment of the substrate was not favourable for DLC growth as it essentially provided for a secondary re-sputtering process. Quality DLC films with approximately 40 % of the sp3 content were fabricated at the optimal angle of the ion flux to the target of 30º and to the substrate of 0º (parallel to the ion bema axis). The increased ion energy contributed to structural changes in DLC from predominantly sp2 graphitic like bonding to tetrahedral sp3 bonding arrangement

Topics: diamond-like carbon films, discharge plasmas
Publisher: Queensland University of Technology
Year: 2007
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