Plasmas allotropes

Figure 7. Simplified scheme for the allotropes of phosphorous formed by conventional and plasma methods.

Strelnitskii et al. 32) reported a superdense carbon allotrope (4,100 kg-m ) obtained as carbon films formed by radio-frequency condensation of carbon plasmas on cooled substrates the crystalline phase, obtained along with amorphous phase, was studied by electron diffraction and revealed a primitive rhombohedral unit cell with 8 carbon atoms, hence this phase was called Cs, and its structure, as proposed by Stankevich et al. [33] and Biswas et al. [34], involved cubes connected by single bonds (supercubane). Burdett and Lee [9] found the supercubane structure to be less stable than diamond if the constituting atoms have 4 or less electrons per atom, but more stable for electron-rich systems (i. e. >4 electrons per atom). Johnston and Hoffmann [35], observing discrepancies in the crystallographic analysis and the unusual bond length distribution, found that a likely alternative structure for Cs is the body-centered BC-8 structure adopted by the high-pressure y- Si allotrope. 

It is conceivable that a parallel bundle of linear polyyne chains (the carbon allotrope named chaoite or carbyne) may form, via thermally-allowed (4 + 2)-n-electron cycloadditions, six-membered rings which lead to graphene sheets and/or nanotubes. However, the mechanism of nanotube formation in a plasma produced by arc discharge appears to require the presence of a transition metal atom at the rim of the growing nanotube [77 j. 

Many methods have been reported for production of nanodiamonds (NDs) such as laser ablation, " plasma-assisted chemical vapor deposition," autoclave synthesis from supercritical fluids, ion irradiation of graphite, chlorination of carbides, electron irradiation of carbon onions, and ultrasound cavitation. Smaller NDs can be prepared by detonation processes that yield aggregates of NDs with sizes of 4-5 nm embedded in a detonation soot composed of other carbon allotropes and impurities. An explosive mixture having an overall negative oxygen balance provides a source of both carbon and energy for the conversion. Because of their small size (2-10 nm) detonation NDs have also been referred to as ultradispersed, nanocrystalline... 

The Discovery of the Fullerenes. In experiments carried out at Rice University in 1985 associated with the presence of carbon in stars and space [Kroto HW, Heath JR, O Brien SC, Curl RF, Smalley RE (1985) Nature 318 162], the Ceo molecule was discovered. This species is one of the many carbon clusters which can be generated when a plasma of carbon vapor produced in the surface of graphite by laser irradiation is cooled by an inert gas jet. The detection of this type of carbon aggregate which appears to constitute a third allotropic and the first molecular form of carbon by mass spectroscopy is illustrated in Fig. 4.18. 

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