Carbon nanotubes, seamless rolled-up graphene sheets, have attracted much attention since their discovery by Iijima (1). Because of their unique properties, single-walled carbon nanotubes (SWNT) are expected to bring significant breakthroughs in the electronic and mechanical engineering of materials. The controlled tuning of the electronic properties of carbon nanotubes constitutes one of the major challenges for applications of these materials. A promising way to overcome the natural mixing of semiconductor and metallic tubes is intercalation with alkali metals such as rubidium. The full understanding and control of the intercalation process constitute then the fundamental step for the development of this route. Coupled “in situ” Raman spectroscopy and conductivity measurements on rubidium intercalated SWNT were firstly carried out (2). Peculiar profile of the conductivity curve together with the characteristic Raman responses suggest different intercalation sites as a function of the doping rate. Ex situ EXAFS studies were then performed. Our results on saturation phase Rb-doped single-wall carbon nanotube bundles show that rubidium ions have a similar local arrangement as in saturated phases of alkali intercalated graphite (3). Nevertheless, ex situ investigations of such samples do not allow to derive the dependence of the local arrangement with respect to the electronic transport properties. In particular, the intercalation sites (localization of Rb ions within SWNTs bundles) as a function of the doping rate are still unknown. Then, to understand properly the intercalation process, EXAFS experiments have to be combined “in situ” to Raman and electrical measurements in order to find out the correlations between the charge transfer, the structural properties (localization of Rb ions) and the electrical conductivity. Consequently, for this aim, we have developed an experimental “in situ” intercalation chamber for multi spectroscopic analysis under vacuum (10-6 mbar). Recently, our experimental set-up has been successfully used at Soleil synchrotron on the SAMBA beamline. The first results will be discussed in details. [1] Iijima, Nature, 354:56 (1991) [2] N.Bendiab et al, Phys.Rev.B, 63, 153407, (2001) [3] Bantignies et al, Phys.Rev.B, 71, 195419, (2005)

The temperature dependence of the Raman spectrum of a gelatine-based composite material doped with single-walled carbon nanotubes (SWNT@gelatin) is reported. A significant up-shift of the G-mode frequency is observed when the temperature is decreased from room temperature to 20~K. This frequency shift is significantly stronger than the one found for pure thermal effects. In contrast, the features of the radial breathing modes (frequencies and width) display no significant change in the same temperature range. These results are well understood by considering a uniaxial strain on the nanotube induced by the thermal expansitivity mismatch between the nanotube and the surrounding matrix.

The purification of single-walled carbon nanotube (SWCNT) samples was analysed using a multi-technique approach, with structural as well as spectroscopic probes, in order to characterize the samples and to identify important factors for improvement of SWCNT sample quality. The first dry oxidation step (air at 365 degrees C) is shown to have only a weak selectivity for the removal of the amorphous carbon or weakly organized graphitic species as well as resulting in a partial consumption of the SWCNTs. The functionalization of the SWCNTs is highly specific with formation of carboxyl, hydroxyl and carbonyl groups. On the other hand this oxidation step is highly efficient for the oxidation of the catalytic impurities (Ni, Y) which can be easily removed by subsequent acid treatment. A final high temperature treatment indicates some incomplete restoration of the quality of the SWCNT surface. (C) 2009 Elsevier Ltd. All rights reserved.

Carbon nanotubes, seamless rolled-up graphene sheets, have attracted much attention since their discovery by Iijima. Because of their unique properties, single-walled carbon nanotubes (SWNT) are expected to bring significant breakthroughs in the electronic and mechanical engineering of materials. The controlled tuning of the electronic properties of carbon nanotubes constitutes one of the major challenges for applications of these materials. A promising way to overcome the natural mixing of semiconductor and metallic tubes is intercalation with alkali metals such as rubidium. The full understanding and control of the intercalation process constitute then the fundamental step for the development of this route. Coupled “in situ” Raman spectroscopy and conductivity measurements on rubidium intercalated SWNT were firstly carried out. Peculiar profile of the conductivity curve together with the characteristic Raman responses suggest different intercalation sites as a function of the doping rate. Ex situ EXAFS studies were then performed. Our results on saturation phase Rb-doped single-wall carbon nanotube bundles show that rubidium ions have a similar local arrangement as in saturated phases of alkali intercalated graphite. Nevertheless, ex situ investigations of such samples do not allow to derive the dependence of the local arrangement with respect to the electronic transport properties. In particular, the intercalation sites (localization of Rb ions within SWNTs bundles) as a function of the doping rate are still unknown. Then, to understand properly the intercalation process, EXAFS experiments have to be combined “in situ” to Raman and electrical measurements in order to find out the correlations between the charge transfer, the structural properties (localization of Rb ions) and the electrical conductivity. Consequently, for this aim, we have developed an experimental “in situ” intercalation chamber for multi spectroscopic analysis under vacuum (10-6 mbar). Recently, our experimental set-up has been successfully used at Soleil synchrotron on the SAMBA beamline. The first results will be discussed in details.

Multi-walled carbon nanotubes (MWCNTs) were produced in a chemical vapor deposition (CVD) process employing methane and argon as hydrocarbon and carrier gas over supported sol-gel Co-Mo/MgO catalysts. A detailed study about the influence of the gas flow of both hydrocarbon and carrier gas on carbon yield, morphology, structure and graphitization degree is presented. Methane partial pressure, methane total flow rate, as well as the flow ratios of methane to argon and methane to hydrogen (reducing gas) were the parameters systematically varied. The results reveal that high MWCNT yields in the produced materials are strongly related to the methane partial pressure and the methane total flow, while a high degree of graphitization is more closely linked to the use of argon gas as inert atmosphere. (C) 2008 Elsevier Ltd. All rights reserved.

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