Amorphous Carbon structure

Rosato, V., Lascovich, J.C., Santoni, A., and Colombo, L. (1998). On the use of the reverse Monte Carlo technique to generate amorphous carbon structures. Int. 

Opletal G., Petersen T., O Malley B., Snook 1., McCulloch D. G., Marks N. A. and Yarovsky L, Hybrid approach for generating reahstic amorphous carbon structures using Metropolis and Reverse Monte Carlo, Mol Sim... 

A. and Yarovsky. 1., Hybrid approach for generating realistic amorphous carbon structures using Metropolis and Reverse Monte Carlo, Mol. 

Molecular configurations of (a) graphite structure and (b) amorphous carbon structure. 

Chapter 1 contains a review of carbon materials, and emphasizes the stmeture and chemical bonding in the various forms of carbon, including the foui" allotropes diamond, graphite, carbynes, and the fullerenes. In addition, amorphous carbon and diamond fihns, carbon nanoparticles, and engineered carbons are discussed. The most recently discovered allotrope of carbon, i.e., the fullerenes, along with carbon nanotubes, are more fully discussed in Chapter 2, where their structure-property relations are reviewed in the context of advanced technologies for carbon based materials. The synthesis, structure, and properties of the fullerenes and... 

Work on the production and oxidation of SWNT samples at SRI and other laboratories has led to the observation of very long bundles of these tubes, as can be seen in Fig. 2. In the cleanup and removal of the amorphous carbon in the original sample, the SWNTs self-assemble into aligned cable structures due to van der Waals forces. These structures are akin to the SW nanotube crystals discussed by Tersoff and Ruoff they show that van der Waals forces can flatten tubes of diameter larger than 2.5 nm into a hexagonal cross-sectional lattice or honeycomb structure[17]. 

Solid carbon materials are available in a variety of crystallographic forms, typically classified as diamond, graphite, and amorphous carbon. More recently another structure of carbon was identified—namely the fullerenes which resemble a soccer ball... 

The crystal structure of graphite and amorphous carbon is illustrated by the schematic representations given in Fig. 1. 

Ni3C decomposition is included in this class on the basis of Doremieux s conclusion [669] that the slow step is the combination of carbon atoms on reactant surfaces. The reaction (543—613 K) obeyed first-order [eqn. (15)] kinetics. The rate was not significantly different in nitrogen and, unlike the hydrides and nitrides, the mobile lattice constituent was not volatilized but deposited as amorphous carbon. The mechanism suggested is that carbon diffuses from within the structure to a surface where combination occurs. When carbon concentration within the crystal has been decreased sufficiently, nuclei of nickel metal are formed and thereafter reaction proceeds through boundary displacement. 

McCuUoch, D. G. and Merchant, A. R., The Effect of Annealing on the Structure of Cathodic Arc Deposited Amorphous Carbon Nitride Films, Thin Solid Films, Vol. 290, 1996, pp. 99-102. 

Fig. 3 shows the Raman spectra of the MWNT samples as a flmction of helium pressure. The peaks around 1280 cm", called the D-mode, are Imown to be attributed la amorphous carbons and defects of nanotubes, whereas the pe around 1600 cm", called the G-mode, are known to be due to the graphitic structure of carbon atoms. The G-mode of produced MWNTs was shifted to a lower wave number region (1595 cm" ) by the strain of the forming tube [6]. The intensity of MWNTs synftiesized under 250 Torr was lower than at other pressure. And the ratio of the G-mode to the D-mode was the hi t at pressure of 500 Torr. The highest purity of MWNTs was obtained when the pressure of helium is 500 Torr. 

This picture was found to be consistent with the comparison of Raman spectra and optical gap of a-C H films deposited by RFPECVD, with increasing self-bias [41], It was found that both, the band intensity ratio /d//g and the peak position (DQ increased upon increasing self-bias potential. At the same time, a decrease on the optical gap was observed. Within the cluster model for the electronic structure of amorphous carbon films, a decrease in the optical gap is expected for the increase of the sp -carbon clusters size. From this, one can admit that in a-C H films, the modifications mentioned earlier in the Raman spectra really correspond to an increase in the graphitic clusters size. 

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