In this paper, we compare the Raman responses obtained on individual suspended Single-Walled Carbon Nanotubes (SWNTs) and Double-Walled Carbon Nanotubes (DWNTs). We focus on the comparison of the frequencies, line widths, intensities and resonance conditions of the main Raman active modes measured on an index-identified DWNT with those measured on SWNTs having atomic structures close to the inner and outer tubes of the DWNT. By this way, we state that the relation between the radial breathing mode frequencies and the diameters established for SWNTs do not work in DWNTs. We found that resonance of only one tube can be sufficient to observe the response of the coupled layers in DWNTs. These results are understood in terms of mechanical coupling between the layers in DWNTs. We evidence that the spectral line widths of the Raman active modes are systematically narrower for DWNTs compared to the corresponding SWNTs. Finally, we present the measurements of the G modes of two different DWNTs which behave in a different way. For the first one, the frequencies of the G modes are not significantly affected by the interaction between the layers, while for the second one we evidence a downward shift of the LO and TO bands arising from the inner layer.

We report in situ Raman scattering experiments on single-layer graphene (SLG) and Bernal bilayer graphene (BLG) during exposure to rubidium vapor. The G- and 2D-band evolutions with doping time are presented and analyzed. On SLG, the extended doping range scanned (up to about 1014 electrons/cm2) allows the observation of three regimes in the evolution of the G-band frequency: a continuous upshift followed by a plateau and a downshift. Overall the measured evolution is interpreted as the signature of the competition between dynamic and adiabatic effects upon n-doping. Comparison of the obtained results with theoretical predictions indicates however that a substrate pinning effect occurs and inhibits charge-induced lattice expansion of SLG. At low doping, a direct link between electrostatic gating and Rb doping results is presented. For BLG, the added electrons are shown to be first confined in the top layer, but the system evolves with time toward a more symmetric repartition of the added electrons in both layers. The results obtained on BLG also confirm that the slope of the phonon dispersion close to the K point tends to be slightly reduced at low doping but suggest the occurrence of an unexpected increase of the phonon dispersion slope at higher electron concentration.

Merging the fields of carbon nanotubes (NTs) and of organic semiconductors opens a wide range of fundamental investigations and potential applications. We developed a two step covalent functionalization method in order to graft complex Pi-conjugated systems on NT sidewalls. In a first step, iodoaniline or iododiphenylacetylene is anchored via the diazonium reaction. Several organometallic coupling reactions, as illustrated on figure 1, have been tested as a second step. The simpliest hybrid systems obtained are illustrated on figure 1 but several other much more complex have been successfully grafted. The hybrid systems obtained have been studied by resonant Raman spectroscopy, XPS, optical absorption and photoluminescence. The impact of functionalization on the properties of both moieties will be discussed and the different chemical reactions used will be compared.

The atomic structure of ultra-long carbon nanotubes grown by catalytic chemical vapor deposition has been studied along the nanotube length via electron diffraction and high-resolution transmission electron microscopy. Contrary to other techniques, electron diffraction studies provide a direct determination of the chiral structure of nanotubes. These studies demonstrate that the chirality of the nanotubes remained constant all along their length. A tendency to double-walled nanotubes has been observed, as well as, a preferential distribution to armchair configuration. Furthermore, the studies yield a metallic:semiconducting ratio close to the one expected from a natural distribution of nanotubes (1:2).

The Raman bands intensities, frequencies, widths and profiles of few layer graphene (FLG) are extremely sensitive to doping, strain, stacking order, number of graphene sheets, crystalline quality and laser wavelength. For samples of epitaxial graphene grown on silicon carbide, the laser wavelength is basically the only factor known a priori. Furthermore, the concomitance of second order SiC Raman modes in the graphene G and D bands region complicates the extraction of the graphene signal. Developing a robust characterization tool enabling to disentangle all these effects and to provide reliable information is thus highly needed and challenging. We propose an approach where micro-Raman spectroscopy is combined with reflectivity and transmission measurements to discriminate between the different contributions in the measured Raman signatures and to access to the detailed characteristics of the samples. Here, we demonstrate the efficiency of this method in order to determine the number of graphene layers. We address then the question of using the 2D band width or ratio of the 2D and G bands intensities as a criteria to distinguish between mono and multi layer(s) graphene.

The thermal stability of catalytic precursors is of major importance for the synthesis of single-walled carbon nanotubes (SWNTs) with narrow diameter distributions by chemical vapor deposition at high temperature. We report a study of the thermal stability of iron (Fe) and iron oxide (Fe2O3) nanoparticles with narrow size distribution grown onto Si/SiO2 hydroxylated flat substrates. Whereas the Fe2O3 nanoparticles are thermally stable up to 900 °C, above their reducing temperature of ∼700 °C, the size distribution of Fe nanoparticles increases and broadens. An accurate analysis of atomic force microscopy data shows that this instability is due to a diffusion−coalescence mechanism, ruling out a possible Ostwald's ripening mechanism. The origin of this behavior is attributed to the dewetting of the nanoparticles. Using the thermally stable oxide nanoparticles as catalytic precursors, SWNTs can be successfully grown using a methane−hydrogen mixed gas. Statistical analysis of the SWNTs Raman radial breathing modesmeasured using four excitation wavelengths indicates that the diameter distribution of the nanotubes is centered at 1.3 ± 0.03 nm with a narrow full width at half-maximum of 0.3 ± 0.05 nm. The analysis of our results compared with other results recently published suggests that the metal−surface interaction could play a key role in the catalytic decomposition of methane and in the growth of SWNTs.

In this paper, we discuss the low-frequency range of the Raman spectrum of individual suspended index-identified single-walled (SWCNTs) and double-walled carbon nanotubes (DWCNTs). In SWCNTs, the role of environment on the radial breathing mode (RBM) frequency is discussed. We show that the interaction between the surrounding air and the nanotube does not induce a RBM upshift. In several DWCNTs, we evidence that the low-frequency modes cannot be connected to the RBM of each related layer. We discuss this result in terms of mechanical coupling between the layers which results in collective radial breathing-like modes. The mechanical coupling qualitatively explains the observation of Raman lines of radial breathing-like modes, whenever only one of the layers is in resonance with the incident laser energy.