Electronic structure of dense amorphous carbon

Lee, Choon H.; Lambrecht, Walter R. L.; Segall, B.; Kelires, P. C.; Frauenheim, Thomas; Stephan, U.

doi:10.1103/physrevb.49.11448

Cited by 49 publications

(17 citation statements)

References 28 publications

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“…7 Thus, the sp 2 sites are unlikely to form large clusters, as noted by molecular dynamics calculations. [8][9][10] The lack a D peak in the Raman spectra of as deposited ta-C films 11 also confirms experimentally that large clusters do not exist in ta-C. Lee et al 12 showed that the band gap could be controlled by the distortion of small rings or chains, instead of the size of the clusters. It has also been shown empirically that the band gap of all forms of a-C and a-C:H depend on the sp 2 fraction.…”

Section: Introductionmentioning

confidence: 78%

Effect of graphitic inclusions on the optical gap of tetrahedral amorphous carbon films

Teo¹,

Rodil²,

Tsai³

et al. 2001

Journal of Applied Physics

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High sp 3 fraction tetrahedral amorphous carbon (ta-C) films can be prepared using the filtered cathodic vacuum arc ͑FCVA͒. A by-product of the deposition process are small micrometer sized graphitic particles which are also incorporated into the film. The particle coverage of FCVA films is typically Ͻ5%, and thus the effect of these graphite inclusions have been largely ignored in earlier optical gap measurements of ta-C. By incorporating a better filter design ͑e.g., S-bend filter͒, the particle coverage can be reduced to 0.1%. In this article, we show that the effect of these graphitic inclusions is to scatter or absorb light which significantly affects the optical gap measurement and hence reduces the ''apparent'' optical gap of the ta-C film. By comparing two ta-C films with different particle coverage but the same sp 3 content of 85%, we show that we can correct for the effect of these inclusions. Our results confirm that the E 04 gap of a 85% sp 3 ta-C matrix is 3.6 eV. The importance of considering these micro particles is emphasized as we find that for every 1% of area covered by particles, there is a 3-4 fold percentage difference between the corrected optical gap and measured gap of the film.

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Section: Introductionmentioning

confidence: 78%

Effect of graphitic inclusions on the optical gap of tetrahedral amorphous carbon films

Teo¹,

Rodil²,

Tsai³

et al. 2001

Journal of Applied Physics

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“…No simulations have produced aromatic microstructures in published models, 5 and are unlikely to given the high atom density of a-tC. Fourfoldcoordinated structures such as BC8, and structures with threefold atoms and double bonds serve as better tests of transferability.…”

Section: Discussionmentioning

confidence: 99%

Small rings and amorphous tetrahedral carbon

1999

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We apply first-principles density-functional calculations to study strain in dense amorphous tetrahedral carbon (a-tC). While the large strain present in small-ring structures, particularly three-member rings, could argue against their existence in a-tC, we demonstrate, based on energetic arguments, that strained small ͑threeand four-member͒ rings are plausible topological microstructural elements. We present two bulk carbon structures made up entirely of fourfold-coordinated atoms: the first with every atom in one three-member ring, the second with every atom in one four-member ring. Calculations show these bulk ring structures are relatively low in energy, only 0.37 and 0.23 eV/atom above diamond, respectively. This computed strain energy is much less than that present in recent models for a-tC. We examine properties of these structures with the intention to provide benchmark calculations for more approximate models, and to investigate the impact small rings might have on the properties of a-tC. We use a recently developed linear-response algorithm to compute phonon spectra for these ring structures.

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“…It was shown that the typical value of E g ∼ 1 eV, which is characteristic for amorphous carbon, can be obtained for a single 6-fold ring with a "chair" distortion. The role of a ring distortion was also discussed by Lee et al [12].…”

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confidence: 86%