Diamond coatings on graphite for plasma facing materials

Abstract

Nanocrystalline and microcrystalline diamond lms have been successfully deposited on graphite substrates for the rst time. The morphology of the lms depended on the experimental parameters used during deposition such as: gas mixture, excitation power, pressure and deposition time, along with nucleation treatments. Experiments are reported for removing non-diamond carbon material from commercial detonation nanodiamond used for seeding nucleation. Scanning Electron Microscopy (SEM), Raman Spectroscopy and X-ray Photoelectron Spectroscopy (XPS) techniques were used to characterise the samples. Optical Emission Spectroscopy (OES) and Mass Spectroscopy were used to analyse the species formed in the gas phase during diamond growth. We observed that the excitation power used during deposition a ects mainly the diamond crystallite size. Microcrystalline lms were obtained when the excitation power was 3.0 and 3.6 kW and nanodiamond lms were observed when 1.5 kW was used. The use of argon is essential for growing diamond on graphite and the methane content a ects the morphology, the sp3/sp2 content and the crystallite size of the lms. When using less than 5% of methane in the gas mixture, f100g faces are predominant even after long periods of deposition. Using 5% of methane results in a lm with cauli ower-like structure. Change in the morphology caused by secondary nucleation was observed after long deposition periods of time. To study the behaviour of our prepared samples under erosion conditions, diamond lms were exposed to hydrogen plasma etching and analysed in terms of lm quality (sp3/sp2 content) and growth/etching mechanisms. Finally, there is also included a study about the production of carbon bres on diamond lms during hydrogen plasma exposure in the presence of silicon.