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.