Nanocrystalline Diamond Films Deposited By Hot Filament CVD

Nano-crystalline diamond(NCD) films were deposited on different substrates(single crystal Si(100),stainless steel sheets and Ti sheets) using CH₄/H₂ gas mixtures in a hot filament chemical vapor deposition(CVD) system.The influence of the gas pressures,CH₄ concentrations,Ar concentrations and the negative pulsed biases on the surface morphology, microstructures,residual stress of the films was analyzed by scanning electron microscopy (SEM),atomic force microscopy(AFM),X-ray diffraction(XRD)and Raman spectrometry and transmission electron microscopy(TEM).The experimental results showed that the crystal size was observed to decrease with the decrease of the gas pressure.The deposited films were confirmed the presence of crystalline diamond by XRD diffraction peaks at 43.9°,75.3°and 91.5°corresponding to the(111), (220) and(311) crystal faces.NCD films were synthesized at the pressure of 2×10³pa because the evidence for NCD was taken as the presence of the 1150cm^-1 Raman line.The grain sizes decreased from micron to nanometer dimensions with the increases of Ar concentration in the Ar/CH₄/H₂ system which resulted in the residual stress changed from an intrinsic tensile stress to the compressive stress in the films.And the residual compressive stress increased first and then reduced with increasing Ar content.When the Ar concentration was raised to 98%,it was found that the film consisted of nano-crystalline diamond grains and amorphous carbon by TEM.When the Ar concentration was kept at 33%,the grain size decreased and the residual tensile stress increased with the CH₄ addition.The deposited films were diamond-like carbon(DLC) films with high optical transparency by applying a negative pulsed bias to the substrate at the low pressure of 3.7Pa.It was found that the grain size and the roughness reduced to a minimum value and then rapidly increased when the pulse bias was increased.Diamond film can be deposited on the stainless steel substrate by using interlayer such as poly-silicon.Poly-silicon as interlayer can improve the adhesion strength of diamond film on the stainless steel substrate.Diamond films on metallic titanium were prepared by the formation of an intermediate TiC layer,which leaded to good adhesion between the Ti substrate and the diamond film.