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We report an investigation of few layers graphene exfoliated on SiC. Using AFM and Raman spectroscopy, we find that the graphene thickness determined from the normalized intensity of Raman lines significantly depart from the one obtained using XPS.

Ref HAL: hal-00512694_v1
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Adsorption of specifically designed polyaromatic amphiphiles were used to sort HjPCo single-walled carbon nanotubes (SWNTs) with different helicities. The sorting is investigated by resonant Raman excitation profiles. Chiral indexes (n and m) of SWNTs present in our samples are determined by fitting the Raman peaks observed in the radial breathing modes region (RBM). Scanning over an excitation energy range between 2 and 2.2 eV with a 0.01 eV step allows to investigate mainly two families of metallic nanotubes (2n + m = 24 and 2n + m = 27). The transition energies of nanotubes measured from the Raman spectra differ from the calculated ones, leading to useful corrections of the Kataura plot. The results also display significant differences between the sorted and the reference samples, meaning that discrimination between SWNTs of different properties is possible. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Ref HAL: hal-00276997_v1
Ref Arxiv: 0805.0511
DOI: 10.1103/PhysRevB.78.113407
WoS: 000259690800025
Ref. & Cit.: NASA ADS
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187 Citations
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We compare the main feature of the measured Raman scattering spectra from single layer graphene with a bilayer in which the two layers are arbitrarily misoriented. The profiles of the 2D bands are very similar having only one component, contrary to the four found for commensurate Bernal bilayers. These results agree with recent theoretical calculations and point to the similarity of the electronic structures of single layer graphene and misoriented bilayer graphene. Another new aspect is that the dependance of the 2D frequency on the laser excitation energy is different in these two latter systems.

Ref HAL: hal-00496385_v1
PMID 18540661
DOI: 10.1021/nl0803141
WoS: 000257504500009
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75 Citations
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Adsorption of specifically designed and geometrically constrained polyaromatic amphiphiles on single-walled carbon nanotubes (SWNTs) was found to be selective of the nanotube helicity angle. Starting from the same SWNT mixture, photoluminescence and resonant Raman spectroscopies show that a pentacenic-based amphiphile leads to the solubilization of armchair SWNTs and that a quaterrylene-based amphiphile leads to the solubilization of zigzag SWNTs. The results were predicted by the design of the two amphiphiles and are consistent with a supramolecular recognition of the nanotube graphene-type atomic structure by the aromatic part of the molecules through optimized pi-pi(-) stacking interactions.

Ref HAL: hal-00512611_v1
DOI: 10.1103/PhysRevB.75.155432
WoS: 000246075300128
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40 Citations
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By combining, on the same freestanding single-walled carbon nanotubes, electron diffraction and Raman experiments, we were able to obtain the resonance energy of unambiguously (n,m)-identified single-walled carbon nanotubes. We focus on the analysis of the first optical transition of metallic tubes (E-11(M)) and the third and fourth transitions of semiconducting tubes (E-33(S) and E-44(S), respectively) in comparison with calculated values using a nonorthogonal tight-binding approach. For semiconducting tubes, we find that the calculated energies E-33(S) and E-44(S) have to be corrected by non-diameter-dependent (rigid) shifts of about 0.43 eV and 0.44 eV, respectively, for tubes in the 1.4-2.4-nm-diameter range. For metallic tubes in the 1.2-1.7-nm-diameter range, we show that a rigid shift (0.32 eV) of the calculated transition energy also leads to a good estimation of E-11(M). The rather large and non-diameter-dependent shifts for the third and fourth transitions in semiconducting tubes question a recent theoretical study, which relates the shifts to electron-electron correlation and exciton binding energy and suggest that the exciton binding is very small or missing for the higher transitions E-33(S) and E-44(S), contrary to the lower transitions E-11(S) and E-22(S).

Ref HAL: hal-00498157_v1
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The goal of our "complete experimental" approach was to relate the Raman response of an individual single-walled carbon nanotubes (SWNT) to its (n,m) structure determined from an independent way. In this aim, a procedure including transmission electronic microscopy (TEM), Raman spectroscopy, and electron diffraction experiments on the same SAINT has been developed. The independent determinations of both structure and Raman features of semiconducting and metallic nanotubes allows to discuss several questions concerning: (i) the relation between diameter of the tubes and the radial breathing mode (RBM) frequency, (ii) the values and the nature of the E-33(S) and E-44(S) optical transition energies. (c) 2007 WELEY-VCH Veriag GmbH & Co. KGaA, Weinheim.

Commentaires: 0370-1972