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Thin films of curved surface nanocrystalline diamond (CS-NCD) are a category of important materials. However, the development of such materials is still a highly challenging task. Here we present a novel approach to synthesizing CS-NCD thin films deposited on non-spherical surfaces of molybdenum substrate using direct current plasma jet chemical vapor deposition. A special cooling system was designed and applied to ensure uniform substrate temperature. It is demonstrated from simulation and experimental results that this system is favorable for the production of thin films. The results show that the quality of CS-NCD thin films depends on the selection of optimal values of parameters including CH4 concentration, substrate temperature, and chamber pressure. If the CH4 concentration and/or the substrate temperature is too high or low, it results in non-diamond phase or micron-crystalline diamond thin films. Synthetic CS-NCD thin films using the proposed method have a smooth surface and uniform thickness. The average grain size and the mean surface roughness are approximately 30 and 4.3 nm respectively. Characteristics of CS-NCD thin film spectra comprised of the full width at half maximum with broad Raman peaks around 1,140 and 1,480 cm-1, confirming the presence of the NCD phase.

The effect of the substrate temperature and CH4 concentrations on the fracture behavior of thin polycrystalline diamond films was systematically investigated by X-ray diffraction and scanning electron microscopy. The results show that the fracture behavior of thin polycrystalline diamond films synthesized by direct current plasma jet chemical vapor deposition is closely related to the substrate temperature and CH4 concentrations. A high substrate temperature, due to difference in the thermal expansion coefficients of the substrate and the diamond film, causes thin polycrystalline diamond films to generate high residual stresses, which usually exceed fracture strength of thin diamond film and even that of diamond. The fracture toughness is found to drop with the increasing ratio of CH4 concentration. In case of high CH4 concentrations, various defects and impurities, such as cracks, microscopic holes, graphite, and amorphous carbon were observed in the films. Thus, the substrate temperature and CH 4 concentrations should be strictly controlled within an appropriate range

In this paper, mechanisms of defect and crack initiation in a diamond film prepared at substrate temperatures are investigated using direct current plasma chemical vapor deposition method. The study is by way of X ray diffraction (XRD), optical microscope (OM), and scanning electron microscopy (SEM) and reveals that initiation of defects and cracks during the growth of diamond films depends strongly on substrate temperature. The defects and impurities formed in high substrate temperatures include mainly residual stresses, and non-diamond phase such as graphite and amorphous carbon, which result in forming crack and microscopic hole in diamond film. X ray diffraction, optical microscope and SEM have been used to examine the temperature dependence of various defect inductions. It is found that cracks in diamond film are generally derived at grain boundary. In general, diamond films prepared in high temperature substrate will result in high residual stress at the interface between the diamond film and the substrate.