Abstract
Diamond nanoparticles have been synthesized using various methods. Nanodiamonds generated in the gas phase were captured on the membrane of a transmission electron microscope grid during a hot filament chemical vapor deposition (HFCVD) diamond process. In total, ~600 nanoparticles, which were captured for 10 s in six conditions of the capture temperatures of 900 °C, 600 °C and 300 °C and the gas mixtures of 1% CH4-99% H2 and 3% CH4-97% H2, were analyzed for phase identification using high-resolution transmission electron microscopy and fast Fourier transformation. Hexagonal diamond, i-carbon, n-diamond, and cubic diamond were identified. The observation of two or more carbon allotropes captured on the same membrane suggested their coexistence in the gas phase during HFCVD. The crystal structure of carbon allotropes was related to the size of the nanodiamond. The crystal structure of the nanoparticles affected the crystal structure of diamond deposited for 8 h. Confirmation of various carbon allotropes provides new insight into the nanodiamond synthesis in the gas phase and the growth mechanism of HFCVD diamond.
Highlights
Diamond has been synthesized using high-pressure/high-temperature methods [1], and plasmadischarge-stimulated chemical vapor deposition (CVD) [2,3] and hot filament CVD (HFCVD) [4].In addition to the synthesis of diamond bulks or films, nanodiamonds could be synthesized by detonation [5], laser ablation [6], plasma-assisted CVD [7], ion irradiation of graphite [8], electron irradiation of carbon onions [9], ball milling of high-pressure/high-temperature diamond [10] and ultrasound cavitation [11]
Cubic diamond and n-diamond allotropes were dominant in the gas mixture of 1% CH4 -99% H2, whereas nanoparticles of i-carbon allotropes were more dominant in the gas mixture of 3% CH4 -97% H2
When comparing the crystal structures of captured nanoparticles and diamond particles deposited for 8 h, the nanoparticles captured at 1% CH4 -99% H2 were grown as well-faceted diamond particles, whereas the nanoparticles at 3% CH4 -97% H2 were grown as cauliflower diamond particles
Summary
Diamond has been synthesized using high-pressure/high-temperature methods [1], and plasmadischarge-stimulated chemical vapor deposition (CVD) [2,3] and hot filament CVD (HFCVD) [4]. In addition to the synthesis of diamond bulks or films, nanodiamonds could be synthesized by detonation [5], laser ablation [6], plasma-assisted CVD [7], ion irradiation of graphite [8], electron irradiation of carbon onions [9], ball milling of high-pressure/high-temperature diamond [10] and ultrasound cavitation [11]. Park et al [17] succeeded to confirm the generation of non-agglomerated diamond nanoparticles in the gas phase under the synthesis condition of diamond films by HFCVD. Their result showed that non-agglomerated high quality nanodiamonds can be synthesized using a HFCVD reactor. The analysis of the nanoparticles by high resolution TEM (HR-TEM) and fast during HFCVD using a capturing apparatus under various processing conditions. Shown to be related to the crystal structure of the deposited diamond
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