Homogeneous nucleation of diamond powder in the gas phase

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.

Studies on nucleation process in diamond CVD: an overview of recent developments

“…However, there is evidence that, at least in some cases, diamond can be nucleated homogeneously in the gas phase [52][53][54]. Derjaguin and Fedoseev [46] presented theoretical arguments, based on the classical nucleation theory, that homogeneous nucleation is possible.…”

“…A limited number of experiments [52][53][54] have been conducted to examine homogeneous nucleation of diamond in the gas phase at atmospheric and subatmospheric pressures. The number of diamond particles collected from the gas phase is very small compared to typical nucleation densities observed on substrate surfaces.…”

Nanodiamonds and wildfire evidence in the Usselo horizon postdate the Allerød-Younger Dryas boundary

“…Lonsdaleite is especially of interest because, in nature, it is reported only in meteorites (7) or in relation to impact craters (8,9), and is generally formed through shock deformation of graphite or diamond. Lonsdaleite has, therefore, been previously taken as evidence for shock impact formation (9), although it can also be created in low quantities during carbon vapor deposition (CVD) (10,11). Furthermore, the presence of lonsdaleite in impact craters has been challenged and the use of nanodiamonds as a diagnostic criterion for an impact is still debated (8,9,12,13).…”

Структурные Разновидности Политипов

“…Эти максиму-мы могут быть значительно " размыты" для политипов с большими значениями периода повторяемости слов или его случайной упаковкой слоев. К настоящему вре-мени экспериментально получены различные политипы алмаза: 2H [18], 3C, 4H [19], 6H [20,21], 8H [22,23], 9R [24], 15R [25], 21R [26] и др. Однако выводы об их наличии были сделаны по дифракционным данным электронографии и рентгеноструктурного анализа, кото-рые, как указано выше, не могут быть строгим доказа-тельством.…”