A 30 kW-powered DC Arcjet Plasma enhanced chemical-vapor deposition (CVD) system was applied to grow diamonds which included the nano-crystal free-standing film, the nano-/micro-crystal layered free-standing film, the gradient micro-crystal free-standing film and the millimeter-sized grain. The free-standing film quality, such as the roughness, the sp2 content, the residual stress and the grain morphology, was studied by an atomic force microscope (AFM), Raman spectra, a scanning electron microscope (SEM) and a high resolution electron microscope (HREM). In large-sized grain deposition, as-grown deposit was obtained about 1 × 1 × 1 mm3 in size under the condition of 10 μm/h of the substrate moving speed without Nitrogen enhancement. Characterized by Raman spectra and Laue back reflection X-ray diffraction, the deposit was proven to be single crystal diamond with small grains coving its surfaces. The growth rate was about 30 μm/h. Optical emission spectrum (OES) was utilized to characterize gas phases in the plasma for diamond deposition. The mean electron temperature (Te) in the plasma was calculated based on the value of the emission intensity ratio of IHγ/IHβ. Te varied from 0.33 eV to 0.5 eV depending on the concentration of CH4 in H2 from 1.0% to 25%. C2 radical was found to be the dominant carbon source compared with CH radical. The influence of the radical on the morphology of diamond was discussed. It was found that the nano-crystal could be grown when the ratio of the emission intensity, IC2/ICH, was larger than 8.

Optical emission spectroscopy (OES) was used to in situ detect the intensity variation of C2 radical with the deposition time in the boundary layer during homo-nucleation of CVD diamond by DC Arcjet Plasma. The obvious drop and fluctuation of the optical emission intensity were found during the early growth stage. The samples grown after selected deposition time were characterized by micro-structural probes (transmission electron microscope (TEM), high resolution electronic microscope (HREM), selected area diffraction (SAD) and electron energy loss spectra (EELS)), in order to determine the occurrence of the diamond nucleation. Based on the results of the OES and the micro-structural probes, it was revealed that the variation of the optical emission intensity corresponded to the diamond nucleation. The incubation period and the lasting time of nucleation were thus deduced as 6–8min and 20–60s depending on the concentration of CH4 in H2. The incubation period decreased and the lasting time of nucleation increased with the increase of the concentration of CH4 in H2.

Self-standing diamond films were fabricated by a 30 kW DC Arcjet CVD system. The novel progresses, including layer-structured film (nano-/micro-crystalline layer) fabrication, high orientated film deposition with high growth rate at very high ratio of CH4/H-2, crack-free thick and large area films growth, and single crystal fabrication, were reported.Layer-structured self-standing films, 2- and 4-layered ones, were fabricated by fluctuating the ratio of methane to hydrogen with deposition time. Results of scan electronic microscopy (SEM) and Raman spectra showed that the layered films were constructed by the micro-crystalline grains layer / nano-crystalline grains layer. The residual stress within the films were balanced, and even diminished in the certain layer. The layer containing nano-crystalline grains due to a plenty of secondary nucleation could weakly inherit the columnar growth feature of the overlaid layer containing micro-crystalline grains. The grain size and growth orientation of the layer containing micro-crystalline grains could be adjusted by introduction a mid-layer containing nano-crystalline grains. Growth rate was over 10 mu m/hr in layered film fabrication.The effect of very high concentration of CH4 in H-2, 10%<= CH4/H-2 <= 25%, was studied on the film morphology and orientation. Diamond films with morphology containing nice faceted micro-sized grains were obtained with CH4/H-2 up to 17%. The film composition change was found by Raman spectra. High (111)-oriented films were deposited under the condition of CH4/H-2=15% at the maximum growth rate about 50 mu m/h. Deposition temperature could influence both the morphology and orientation of the diamond films. The higher deposition temperature, the higher CH4/H-2 could be allowed to deposit micro-sized grain-containing films. However, high deposition temperature would spoil (111)-orientation. As a consequence, (220) and (311) would be enhanced.Crack patterns occurring in self-standing films were classified as network shape, river shape and circle shape. The distribution and style of dominating crystalline surface was found to influence the strength of self-standing film. The films with 60-120mm of diameter and 2mm of thickness were successfully deposited by controlling of dominating crystalline surface in the films.A new approach to single diamond crystal fabrication by arc jet was proposed and discussed. This method was named as "stable-tip" method which was applied to overcome the morphology instability. Single crystal, 1x1x0.6mm(3) in size, was successfully fabricated by this method. The synchrotron radiation topography was adopted to characterize this single crystal diamond.

Layered self-standing diamond films, consisting of an upper layer, buffer layer, and a lower layer, were fabricated by fluctuating the ratio of methane to hydrogen in high power dc arc plasma jet chemical vapor deposition. There were micrometer-sized columnar diamond crystalline grains in both upper layer and lower layer. The size of the columnar diamond crystalline grains was bigger in the upper layer than that in the lower layer. The orientation of the upper layer was (110), while it was (111) for the lower layer. Raman results showed that no sp3 peak shift was found in the upper layer, but it was found and blueshifted in the lower layer. This indicated that the internal stress within the film body could be tailored by this layered structure. The buffer layer with nanometer-sized diamond grains formed by secondary nucleation was necessary in order to form the layered film. Growth rate was over 10μm∕h in layered self-standing diamond film fabrication.

BON film was fabricated as buffer layer by radio frequency plasma enhanced metal-organic chemical vapor deposition with 100 kHz frequency and trimethyl borate precursor. The typical binding energy of each element is 191.5 eV of B1s, 399.4 eV of N1s, and 531.2 eV of O1s in the films detected by XPS. HRTEM showed the film contained amorphous composition and nano-sized crystalline particles. Electrical properties of films were characterized by I–V curve. The order-magnitude of electric conductivity was measured as several tens (·cm)-1. The hardness of BON film was ~ 10 GPa.

Layered self-standing diamond films, two-, three- and four-layered films, were fabricated by varying the ratio of methane to hydrogen in high-power DC arc plasma jet CVD. Results of scanning electronic microscopy (SEM) and Raman spectra showed that the layered films were constructed by the micro-crystalline grains layer/nano-crystalline grains layer. The residual stress within the films were balanced, and even diminished in the certain layer. The grain size was calculated by X-ray diffraction (XRD). The layer containing nanocrystalline grains due to a plenty of secondary nucleation can weakly inherit the columnar growth feature of the overlaid layer containing micro-crystalline grains. The grain size and growth orientation of the layer containing micro-crystalline grains can be adjusted by introduction of a mid-layer containing nano-crystalline grains. Growth rate was over 10mm/h in layered film fabrication.

Dominant crystalline surface of diamond film growth was tried to control by the help of optical emission spectroscopy in situ detection in high power DC arc plasma jet chemical vapor deposition system. The radicals, like CH, C 2 , H γ , H 2 and H β , were strongly influenced by the substrate temperature and the concentration of Ar, H 2 and CH 4 in the feed gas. Altering the deposition parameters, the emission intensities of various radicals changed, and the intensity ratio of C 2 /H β varied more sensitively than that of CH/H β . The diamond films with excellent (111) dominant crystalline surface were deposited by modifying the radicals atmosphere that had a higher intensity ratio of CH/H β and a lower intensity ratio of C 2 /H β , i.e. the intensity ratio of CH/C 2 was higher than 0.41. Very clear columnar crystals shown in the cross-section of the as-grown films indicated the stability of dominant surfaces growth within this atmosphere of radicals. The stable growth was also proven by the results of X-ray diffraction detection vs. deposition time.

Gas phase species were diagnosed by in situ spatially resolved OES in high power DC arc plasma jet CVD system. CH, C2, H were found as main species in this deposition plasma environment. Concentration of species was studied with the variation of deposition parameters such as methane concentration, substrate temperature and gas flow rate. C2 was found to be the most sensitive species to deposition parameters. The electron mean temperature was deduced from Hγ/Hβ, and changed little no matter how the deposition parameters varied. Self-standing diamond films with (111) orientation were grown within the modified species atmosphere where the intensity ratio of CH/C2 was higher than 0.41.