The role of pentagons in the growth of laminar pyrocarbon

Bourrat, Xavier; Lavenac, Jérôme; Langlais, F.; Naslain, R.

doi:10.1016/s0008-6223(01)00223-8

Cited by 34 publications

(14 citation statements)

References 5 publications

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“…The presence of pentagons and heptagons might also induce an average sp 2+ε hybridization. The occurrence of C 5 and C 7 rings within the graphene layers have already been proposed in the case of a low anisotropic matrix such as SL [34]. Furthermore, pentagons could explain the lower value of the sp 2 ratio of SL, as compared to that of the RL or ReL pyrocarbons.…”

Section: Hybridization Of Pyrocarbonsmentioning

confidence: 78%

Quantitative structural and textural assessment of laminar pyrocarbons through Raman spectroscopy, electron diffraction and few other techniques

Vallerot¹,

Bourrat²,

Mouchon³

et al. 2006

Carbon

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164

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In pyrocarbon materials, the width of the Raman D band (FWHM D ) is very sensitive to low energy structural defects (e.g., disorientations of the graphene layers). The correlation between the two parameters, FWHM D and OA (as derived from selected area electron diffraction: SAED), has allowed to differentiate various pyrocarbons unambiguously. Furthermore, the optical properties of pyrocarbons, i.e., the extinction angle, the optical phase shift and the ordinary and extraordinary reflectance, have been accurately determined at 550 nm by means of the extinction curves method. These results are completed by in-plane and out-of-plane dielectric constant measurements by angular resolved EELS. Moreover, the hybridization degree of the carbon atoms has been assessed by the same technique. About 80% of the carbon atoms of the pyrocarbons have a sp 2 hybridization. The lack of pure sp 2 carbon atoms, as compared to graphite, might be explained by the presence of sp 3 -like line defects.

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Section: Hybridization Of Pyrocarbonsmentioning

confidence: 78%

Quantitative structural and textural assessment of laminar pyrocarbons through Raman spectroscopy, electron diffraction and few other techniques

Vallerot¹,

Bourrat²,

Mouchon³

et al. 2006

Carbon

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164

View full text Add to dashboard Cite

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“…Among them, we can cite rough laminar (columnar structures), smooth laminar, and regenerative laminar [258]. High resolution TEM shows columnar and wavy structures (produced by pentagons during the deposition process [259]). Their TEM fringes length was found to be 1.6, 2.3, and 2.6 nm, respectively.…”

Section: Very Defective Carbons: Pyrocarbons Coals and Sootsmentioning

confidence: 99%

A Guide to and Review of the Use of Multiwavelength Raman Spectroscopy for Characterizing Defective Aromatic Carbon Solids: from Graphene to Amorphous Carbons

2017

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sp 2 hybridized carbons constitute a broad class of solid phases composed primarily of elemental carbon and can be either synthetic or naturally occurring. Some examples are graphite, chars, soot, graphene, carbon nanotubes, pyrolytic carbon, and diamond-like carbon. They vary from highly ordered to completely disordered solids and detailed knowledge of their internal structure and composition is of utmost importance for the scientific and engineering communities working with these materials. Multiwavelength Raman spectroscopy has proven to be a very powerful and non-destructive tool for the characterization of carbons containing both aromatic domains and defects and has been widely used since the 1980s. Depending on the material studied, some specific spectroscopic parameters (e.g., band position, full width at half maximum, relative intensity ratio between two bands) are used to characterize defects. This paper is addressed first to (but not limited to) the newcomer in the field, who needs to be guided due to the vast literature on the subject, in order to understand the physics at play when dealing with Raman spectroscopy of graphene-based solids. We also give historical aspects on the development of the Raman spectroscopy technique and on its application to sp 2 hybridized carbons, which are generally not presented in the literature. We review the way Raman spectroscopy is used for sp 2 based carbon samples containing defects. As graphene is the building block for all these materials, we try to bridge these two worlds by also reviewing the use of Raman spectroscopy in the characterization of graphene and nanographenes (e.g., nanotubes, nanoribbons, nanocones, bombarded graphene). Counterintuitively, because of the Dirac cones in the electronic structure of graphene, Raman spectra are driven by electronic properties: Phonons and electrons being coupled by the double resonance mechanism. This justifies the use of multiwavelength Raman spectroscopy to better characterize these materials. We conclude with the possible influence of both phonon confinement and curvature of aromatic planes on the shape of Raman spectra, and discuss samples to be studied in the future with some complementary technique (e.g., high resolution transmission electron microscopy) in order to disentangle the influence of structure and defects.

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“…In this case pentagons and heptagons are trapped in the hexagonal lattice. 18 Layer distortions form Ω-like features in the texture. This produces a structural porosity, which controls the drop in density and anisotropy.…”

Section: Dark Laminar Pyrocarbons (Dl)mentioning

confidence: 99%

Low temperature pyrocarbons: a review

Bourrat¹,

Langlais²,

Chollon³

et al. 2006

J. Braz. Chem. Soc.

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Este artigo é uma síntese das pesquisas recentes na área dos pirocarbonos. Pirocarbono é uma forma de carbono preparada por deposição química em substratos quentes (acima de 900 °C) mediante pirólise de hidrocarbonetos. Aplicações se encontram nas áreas de materiais compósitos termostruturais, de reatores nucleares ou de biomateriais. Muito recentemente, um avanço importante foi obtido na compreensão dos processos de crescimento. Uma classificação dos pirocarbonos de baixa temperatura é apresentada, que se fundamenta na medição da quantia de defeitos e do grau de anisotropia, fazendo uso da espectroscopia Raman. Ela traz uma relacão bem estabelecida entre mecanismos de crescimento, estrutura e propriedades dos pirocarbonos.This article is a synthetic survey of the recent researches in the field of pyrocarbons. Pyrocarbon is the form of carbon which deposits on hot surfaces above 900°C by cracking of hydrocarbons. Applications are in the fields of composite materials, nuclear reactors or biomaterials. Very recently, an important step was reached concerning the understanding of the growth processes. A classification of the low temperature pyrocarbons is introduced. It is based on the measure of carbon defects and anisotropy, using Raman spectroscopy. It provides a comprehensive relationship between growth mechanisms, structure and properties of pyrocarbons.

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The role of pentagons in the growth of laminar pyrocarbon

Cited by 34 publications

References 5 publications

Quantitative structural and textural assessment of laminar pyrocarbons through Raman spectroscopy, electron diffraction and few other techniques

Quantitative structural and textural assessment of laminar pyrocarbons through Raman spectroscopy, electron diffraction and few other techniques

A Guide to and Review of the Use of Multiwavelength Raman Spectroscopy for Characterizing Defective Aromatic Carbon Solids: from Graphene to Amorphous Carbons

Low temperature pyrocarbons: a review

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