Deposition of polycrystalline and nanocrystalline diamond on graphite: effects of surface pre-treatments

The growth of hydrogenated sp³-phase of diamond on the sp²-phase of graphite by Microwave Plasma Enhanced Chemical Vapour Deposition (MPECVD) is a challenge, primarily because hydrogen etches graphite much faster than the growth rate of diamond. To enhance nucleation of diamond on graphite, we used a plethora of techniques such as plasma etching, ion bombardment, manual scratching, and scratching by ultrasonic agitation. Nanocrystalline and polycrystalline diamond thin-films were grown by MPECVD on the surface of pre-treated or pristine graphite using 1.5, 3.0, and 3.6 kW microwave power. Samples were characterised by Scanning Electron Microscopy, Raman Spectroscopy, and X-ray Photoelectron Spectroscopy. Species in the gas phase during film deposition were monitored by Optical Emission Spectroscopy. We have found that the surface area covered and the morphology of the diamond films are dependent on the surface pre-treatment. The crystallite size of the films depends on the microwave power used during MPECVD growth. The results of this study establish the protocols for diamond deposition by MPECVD on graphite substrates with a desired crystalline quality based on the pre-treatment of the substrate and the microwave power used during MPECVD. These results are important to modern applications, such as plasma facing materials, in which diamond has shown outstanding performance in contrast to that of graphite.