Electronic, magnetic, and structural properties of amorphous carbons and the discovery of the fullerenes

Dunne, Lawrence J.; Clark, Anthony D.; Chaplin, Martin F.; Katbamna, Harsha

doi:10.1016/0008-6223(92)90064-4

Cited by 10 publications

(10 citation statements)

References 14 publications

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“…odd-alternate p-type radicals) 20 are formed, the charge carriers travel via tunneling from one metallic island to another. 21 Accordingly, the capacitor-like structure (metallic island/contact resistance/ metallic island) is also generated within aggregated particles. For the MWCN-and BMWCN-films, the presence of a linear and horizontal impedance profile is indicative of the intrinsic resistors, i.e.…”

Section: Tem and Sem Analysesmentioning

confidence: 99%

A low resistance boron-doped carbon nanotube–polystyrene composite

et al. 2001

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Section: Tem and Sem Analysesmentioning

confidence: 99%

A low resistance boron-doped carbon nanotube–polystyrene composite

et al. 2001

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“…In amorphous carbons, prepared by the thermal decomposition of organic materials, paramagnetic centres which give rise to ESR signals can be observed at the onset of charring [14][15][16][17][18]. An analysis of the g-factors for a range of chars [17] indicates that these are typically in the range of values 2.0030-2.0034, consistent with odd-alternant πradical carriers. Hence it appears that the radicals in fullerene soots and chars are not of the same type.…”

Section: Electron Spin-resonance (Esr) Investigationsmentioning

confidence: 99%

Electrical, magnetic and structural characterization of fullerene soots

Dunne

Sarkar

Kroto

et al. 1996

J. Phys.: Condens. Matter

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Although it is some five years since fullerenes were extracted in macroscopic quantities from the black, superficially amorphous sooty deposits produced by a carbon arc under helium, little is known in detail about the structure of the deposit or its electrical and magnetic properties. Here we provide evidence that this deposit, known as fullerene soot, is composed of defective networks of carbon atoms which do not have all valencies satisfied. We have studied these soots, before and after thermal annealing, using x-ray and electron diffraction, electron spin-resonance (ESR) spectroscopy, infra-red transmission and measurements of electrical conductivity. We find that localized states associated with such dangling bonds are removed from the soot on annealing and this process is accompanied by an ordering transition which modifies the electrical and magnetic properties. The fullerene soot particles appear to be encapsulated aggregates of highly defective carbon `onions'. Such metastable defective networks undergo a subtle ordering processes upon heat treatment which is accompanied by a rise in the electrical conductivity and a loss of paramagnetism due to the elimination of unsatisfied carbon atom valencies. Electrical conductivity and infra-red transmission measurements indicate that the centre of these `onions' is graphitic, with metallic properties. The temperature dependence of the electrical conductivity suggests that charge transport in both annealed and unannealed materials occurs by tunnelling between metallic islands in the sample. The ESR linewidth, arising from the spin centres in fullerene soots, is not significantly changed by exposure to oxygen. This suggests that the free radical centres in fullerene soots are extremely efficiently isolated from the atmosphere - presumably by encapsulation. This behaviour contrasts with that of amorphous carbons prepared by thermal decomposition of organic materials (chars). The ESR g-factors of the fullerene soots are lower than those of chars, which suggests that the radicals in fullerene soots have strong sigma character due to unsatisfied -type valencies. In this paper, a plausible structure and associated annealing mechanism for the fullerene soot is presented based on these experimental observations. .

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“…With the exception of HR, all CNTs were photoactive, producing superoxide and/or singlet oxygen, with P2-P and HP best able to produce O 2 À while SG65-P, P2-P and P2-R were most effective at producing 1 O 2 . The basis of the observed photoactivity differences between pure and raw CNTs is outside the scope of this study, but the observations may be due to the scavenging ability of the amorphous carbon associated with raw samples (Dunne et al, 1992). We also tested for OH generation, but did not observe any production of OH (data not shown).…”

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confidence: 93%