Tribological testing of self-mated nanocrystalline diamond coatings on Si3N 4 ceramics

Due to their much lower surface roughness compared to that of microcrystalline diamond, nanocrystalline diamond (NCD) films are promising candidates for tribological applications in particular when deposited on hard ceramic materials such as silicon nitride (Si3N4). In the present work, microwave plasma assisted chemical vapour deposition of NCD is achieved using Ar/H2/CH4 gas mixtures on plates and ball-shaped Si3N4 specimens either by a conventional continuous mode or a recently developed pulsed regime. The microstructure, morphology, topography and purity of the deposited films show typical NCD features for the two kinds of substrate shapes. Besides, tribological characterisation of the NCD/Si3N4 samples is carried out using self-mated pairs without lubrication in order to assess their friction and wear response. Worn surfaces were studied by SEM and AFM topography measurements in order to identify the prevalent wear mechanisms. Friction values reached a steady-state minimum of approximately 0.03 following a short running-in period where the main feature is a sharp peak which attained a maximum around 0.45. Up to the critical load of 35 N, corresponding to film delamination, the equilibrium friction values are similar, irrespective of the applied load. The calculated wear coefficient values denoted a very mild regime (K ~ 1x10-8 mm3N-1m-1) for the self-mated NCD coatings. The predominant wear mechanism was identified as self-polishing by micro-abrasion

High precision pressure sensors based on SAW devices in the GHz range

In this paper, an AlN/free-standing nanocrystalline diamond (NCD) system is proposed in order to process high frequency surface acoustic wave (SAW) resonators for sensing applications. The main problem of synthetic diamond is its high surface roughness that worsens the sputtered AlN quality and hence the device response. In order to study the feasibility of this structure, AlN films from 150 nm up to 1200 nm thick have been deposited on free-standing NCD. We have then analysed the influence of the AlN layer thickness on its crystal quality and device response. Optimized thin films of 300 nm have been used to fabricate of one-port SAW resonators operating in the 10–14 GHz frequency range. A SAW based sensor pressure with a sensibility of 0.33 MHz/bar has been fabricated

Nanocrystalline diamond films grown at very low substrate temperature using a distributed antenna array microwave process: Towards polymeric substrate coating

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Diamond thin film growth by pulsed microwave plasma at high power density in a CH4–H2 gas mixture

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Graphene Synthesis by Microwave Plasma Chemical Vapor Deposition: Analysis of the Emission Spectra and Modeling

International audienceIn this article, we report on some of the fundamental chemical and physical processes responsible for the deposition of graphene by microwave plasma-enhanced chemical vapor deposition (PECVD). The graphene is grown by plasma decomposition of a methane and hydrogen mixture (CH 4 /H 2) at moderate pressures over polycrystalline metal catalysts. Different conditions obtained by varying the plasma power (300-400 W), total pressure (10-25 mbar), substrate temperature (700-1000°C), methane flow rate (1-10 sccm) and catalyst nature (Co-Cu) were experimentally analyzed using the in situ optical emission spectroscopy (OES) technique to assess the species rotational temperature of the plasma and the H-atom relative concentration. Then, two modeling approaches were developed to analyze the plasma environment during graphene growth. As a first approximation, the plasma is described by spatially averaged bulk properties, and the species compositions are determined using kinetic rates in the transient zero-dimensional (0D) configuration. The advantage of this approach lies in its small computational demands, which enable rapid evaluation of the effects of reactor conditions and permit the identification of dominant reactions and key species during graphene growth. This approach is useful for identifying the relevant set of species and reactions to consider in a higher-dimensional model. The reduced chemical scheme was then used within the self-consistent two-dimensional model (2D) to determine auto-coherently the electromagnetic field, gas and electron temperatures, heavy species, and electron and ion density distributions in the reactor. The 0D and 2D models are validated by comparison with experimental data obtained from atomic and molecular emission spectra

Growth processes of nanocrystalline diamond films in microwave cavity and distributed antenna array systems: A comparative study

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Microstructure and biological evaluation of nanocrystalline diamond films deposited on titanium substrates using distributed antenna array microwave system

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Investigation of a distributed antenna array microwave system for the three-dimensional low-temperature growth of nanocrystalline diamond films

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Thick and widened high quality heavily boron doped diamond single crystals synthetized with high oxygen flow under high microwave power regime

International audienceThe aim of this paper is to optimize the growth conditions of thick boron doped diamond single crystals, which requires the use of high microware power density to have high growth rate, in order to allow enlarging CVD deposited layers keeping both high boron doping level and high crystal quality. It is shown that the use of a high amount of oxygen (1 to 2%) in the gas phase leads to 1 mm lateral growth after the growth of 500 μm thick CVD diamond layer. Thus, the surface is increased from 10 mm² to 18 mm². The obtained films exhibit high crystal quality confirmed by Raman spectroscopy and confocal microscopy. Depending on the gas composition introduced in the reactor, the boron concentration varied between 5×1019 at/cm3 and 3×1020 at/cm3 as measured by SIMS