Homogeneous nucleation of diamond powder in the gas phase

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Abstract
Homogeneous nucleation of diamond powder is reported. The experiments were performed in a low-pressure microwave-plasma reactor. The deposits were collected downstream of the reaction zone and subjected to wet oxidation to remove nondiamond carbons. The residues were analyzed by optical and electron microscopy, electron diffraction, and Raman spectroscopy. A variety of hydrocarbons diluted in argon, hydrogen, or oxygen gas mixtures were tested. In most cases only nondiamond materials, like graphite and carbyne, were obtained. Homogeneous nucleation of diamond was clearly observed in dichloromethane- and trichloroethylene-oxygen mixtures. The particles formed had crystalline shapes, mostly hexagonal. The largest particles were about 0.2 μm, although most of the particles were on the order of 50 nm in diameter. The powder was identified to be a mixture of polytypes of diamond.