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.

Des données de spectroscopies Raman sur des nanostructures carbonées individuelles: nanotubes de carbone, simple et double feuillets, et graphène sont présentées et discutées en fonction de prédictions théoriques récentes.

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 work, the infrared active modes are computed for homogeneous bundles of single-walled boron nitride nanotubes (BBNNTs), using the so-called spectral moments method. The dependence of the wavenumber on these modes in terms of diameters, lengths, and numbers of tubes, is investigated. To this end, use is made of a Lennard-Jones potential for describing the van der Waals interactions between tubes in a bundle. We find that, for a finite homogeneous bundle, additional modes appear as a specific signature. Finally, these results are useful for the interpretation of the experimental infrared spectra of BBNNTs.

By combining resonant Raman spectroscopy, high resolution transmission electron spectroscopy (HRTEM) and electron diffraction experiments on individual free-standing carbon nanotubes, we have been able to determine unambiguously the intrinsic features of their phonons. In this communication we review the results obtained from these combined experiments on single-walled (SWNT)and double-walled (DWNT) carbon nanotubes. The features of the Raman-active modes of SWNT and DWNT as a function of their structure is discussed and compared with recent theoretical predictions.

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.