Improvement of nanocrystalline diamond film growth process using pulsed Ar/H₂/CH₄microwave discharges

Abstract

For the first time nanocrystalline diamond (NCD) films were deposited by the pulsed microwave plasma assisted chemical vapour deposition process starting from an Ar/H2/CH4 gas mixture. Comparisons with continuous mode deposition gave evidence for the improvement in film quality when the microwave power was modulated with a pulse repetition rate in the range 50–1000 Hz. A reduction in grain size and surface roughness, especially at low pulse repetition rate, accompanied by a decrease in soot particle formation was observed. A thermo-chemical plasma model, developed for pulsed Ar/H2/CH4 microwave discharges, provides evidence for the fact that the pulsed mode permits the enhancement of the mole fraction of the C2 dimer assumed to be the growth precursor of NCD. This may be responsible for a high secondary nucleation rate improving the nanostructure of the film in pulsed discharges.

Spectroscopic Diagnostics of Pulsed Microwave Plasmas used for Nanocrystalline Diamond Growth

“…[1,4,17] The basic parameters were an Ar/H 2 /CH 4 gas mixture with a composition of 96%/3%/1%, a total gas pressure maintained at 200 mbar, and a surface temperature equivalent to the deposition temperature in the range 850-900 -C. Concerning the pulsed parameters, the pulse repetition rate was varied from 50 to 3000 Hz, keeping a constant duty cycle of 50% and a constant peak power of 1000 W. Under these conditions, the time-averaged microwave power remained unchanged and equal to 500 W. Spectroscopic measurements were also completed for the CW mode with the same parameters and an injected microwave power of 500 W in order to allow comparisons.…”

“…[1] Owing to the existence of two additional degrees of freedom, which are the pulse repetition rate and the duty cycle, i. e., the ratio of the pulse duration to the pulse period, the use of a pulsed wave (PW) is much more flexible than the conventional continuous wave (CW) regime. Therefore PW mode allows the control of the chemical kinetics and energy dissipation in the plasma by adjusting these additional parameters.…”

“…If the C 2 molecule is really a key species in the deposition process of NCD films, this decrease of the time-averaged density in PW mode is very surprising since at low pulse repetition rate the secondary nucleation is improved and the growth rate is comparable to the CW mode. [1,4] However, it should be remembered that BAS and ES measurements are always averaged along the plasma diameter, and that the absorption length probably varies significantly during the microwave pulse period. Moreover, the measurements described here were achieved in the plasma bulk whereas the growing film is in interaction with a thin boundary layer, the composition and temperature of which are expected to deviate from the plasma bulk.…”

“…C 2 ! C conversion channels, [1] and especially at low pulse repetition rate, which could influence the NCD growth process. It is worth noting that at least 6-7 ms of plasma discharge are necessary for the temperature to stabilize (Fig.…”

Impact of laser power density on tribological properties of Pulsed Laser Deposited DLC films

“…On the other hand, films with more sp 3 bonded carbon are hard and chemically inert exhibiting low friction and high wear resistance. [17][18][19] These bonding states of carbon atoms and their properties also depend on substrates used for DLC film deposition. [20][21][22] There are several techniques to deposit DLC film such as cathodic arc, direct ion beam, plasma-enhanced chemical vapour deposition, DC/RF sputtering, ion beam sputtering and pulsed laser deposition (PLD).…”