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Abstract: Synthesis of hexagonal diamond on Al/Ni coated thermally oxidized SiO2 covered Si wafer substrate with photo-enhanced chemical vapor deposition (CVD) method at 450°C is reported here. The Raman spectroscopy on grown samples shows a 1322cm−1 peak with 75.4cm−1 full width at half maximum (FWHM). The X-ray diffraction (XRD) data shows hexagonal diamond peaks. Various stages of hexagonal diamond formation are observed in the scanning electron microscope (SEM) images. Based on these images, a mechanism of hexagonal diamond nucleation and growth is proposed. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]