X-ray and neutron-diffraction investigations of rubidium-intercalated single-walled carbon nanotubes are reported. Ab initio calculations conducted in combination with our experiments show that for a single Rb ion the most energetically favorable intercalation site is the interstitial channel between three tubes in a bundle. At higher doping levels, as the Rb content increases, this site becomes however unfavored with respect to the interior of the tubes or the external surface of the bundle. Model simulations of the diffraction patterns, capable of well reproducing both the x-ray and neutron-diffraction patterns, indicate that only the latter insertion sites are compatible with the experimental data. Finally we show that the bundle surface site is the most probable one in the case of saturation at an estimated stoichiometry close to RbC8.

The electrochemical properties of â-type nickel (oxy)hydroxides Ni(OH)2 and NiO(OH) are known to depend significantly on their structural features. In this work, these features are investigated by means of inelastic neutron scattering and infrared and Raman spectroscopies. Our experiments probe both inter- and intramolecular (40-4000 cm-1) vibrational ranges and particular attention is paid to the low-frequency (40-300 cm-1) domain, where new features are observed. Namely, the presence of an IR active mode at around 130 cm-1, characteristic of the oxidized â-NiO(OH) phase, is observed for the first time. The effects of temperature (10-300 K) and deuteration are also measured in order to provide deeper insight into the nature of the vibrational states. A detailed comparison of all of the collected data allows us to propose a new assignment of the vibrational features observed in both â-Ni(OH)2 and â-NiO(OH) and to quantify the proton dynamic relevance on the vibrational modes. We show that the interlayer interactions are mostly electrostatic and, hence, do not involve hydrogen bonding. We also point out that, in the oxidized â-phase, protons cannot be localized so that they can be considered as fully labile. To sum up, this investigation emphasizes that proton delocalization and crystalline disorder, which arise concomitantly upon oxidation, are the key factors that explain the evolution of the vibrational features observed between the oxidized and reduced â-type forms.

Herein, we report the experimental investigation of the vibrational properties of corannulene using Raman spectroscopy. The temperature dependences of the Raman spectra between 300 and 20 K reveal a very high sensitivity of the low frequency domain between 40 and 200 cm(-1) compared to the intramolecular domain. The behavior of the Raman modes of the corannulene under pressure, between 0.53 GPa and 8 GPa, is also studied. Under pressure, in the intermolecular vibrational domain (<150 cm(-1)), two transitions occur suggesting metastable intermediate stages under pressure. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

In this communication we report the efficiency of Raman spectroscopy to characterize carbon-based nanostructures: single-walled carbon nanotubes and graphene. First, by combining Raman spectroscopy and electron diffraction experiments on individual freestanding single-walled carbon nanotube (SWNTs), we have been able to define Raman criteria allowing the identification of SWNTs from their Raman features only. We present and discuss these criteria which concern [1] (i) the radial breathing mode (RBM) vs diameter relationship, (ii) the profile of the G-modes and the diameter dependence of the frequency of the LO and TO G-mode of metallic and semiconducting SWNTs respectively [2,3] , (iii) The values of the optical transition energies EM11, ES33 and ES44 for individual freestanding SWNTs [4]. We show the efficiency of this metrological approach: (i) to assign the (n,m) indices of individual freestanding single-walled carbon nanotubes, and (ii) to identify the (n,m) tubes organized in a small bundle [5]. On the other hand, the main features of the Raman spectra of single layer graphene, Bernal bilayer and bilayer in which the two layers are arbitrary misoriented are compared. We found, in agreement with recent calculations [6], that the profile of the 2D band of misoriented bilayer graphene is similar to that of single layer graphene, and clearly opposite to the four components found in Bernal bilayer. By contrast with previous statement, we conclude that a unique thin peak of the Raman 2D spectrum is not enough to unambiguously identify single layer graphene [7]. [1] J.C. Meyer et al., Phys. Rev. Lett. . 95 (2005) 217401 [2] M. Paillet, et al., Phys. Rev. Lett. 96 (2006) 257401 [3] S. Piscanec et al., Phys. Rev. B 75 (2007) 35427 [4] T. Michel et al., Phys. Rev. B 75 (2007) 155432 [5] T. Michel et al., Phys. Rev. B (2008) submitted [6] S. Latil et al., Phys. Rev. B 76 (2007) 201402 [7] P. Poncharal et al., Phys. Rev. B 78 (2008) 113407

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