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.

From combined Raman spectroscopy and electron diffraction studies on several freestanding single-walled carbon nanotubes (SWNTs), we define Raman criteria which correlate the main features of the Raman spectrum (radial breathing mode and G modes) and the optical transition energies with the structure of the SWNT under investigation. On this basis, we discuss the possibilities to determine the (n,m) indices of an individual SWNT from a single wavelength Raman experiment. We show the efficiency of this approach in assigning the (n,m) structure of different individual nanotubes including all types of achiral SWNTs. Finally, the limits and the accuracy of the method are discussed.

The Raman spectral signature of folded graphene layers for one to six layers was studied. Folding allows realization of rotational disorder in otherwise perfect samples. We show that the two-dimensional Raman band of the folded sample is up shifted compared to the unfolded sample. The evolution of the spectral signature with increasing number of layers is discussed.

In their Comment, Ni et al. show new data as supporting their hypothesis, i. e., the two-dimensional band blueshift between graphene and misoriented bilayer is caused by a reduction in the Fermi velocity. In the first part of our reply, we will demonstrate that the exhibited data, which typically shows a constant blueshift for various excitation energies are in contradiction with a change in Fermi velocity. In the second part we will explain how charge transfer from the substrate that affects the phonon-dispersion curve can account for the observed discrepancies and how this hypothesis is supported by experimental observations.

Using the spectral moments method, the calculations of the Raman spectra of single-walled boron nitride nanotubes (SW-BNNTs) were performed in the framework of the force constants model. Spectra were computed for chiral and achiral nanotubes for different diameters and lengths. The Raman scattering intensities were determined using the bond-polarizability model and a good agreement with group theory analysis was found. We show that the modes in the low frequency region are very sensitive to the nanotube diameter variation, whereas the ones associated to the tangential region are chirality dependent. The number of Raman active modes, their frequencies, and intensities depend on the length of the nanotube. (C) 2009 Elsevier B.V. All rights reserved.

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.

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