Low frequency vibrations observed on assemblies of vertical multiwall carbon nanotubes by Brillouin light scattering: determination of the Young modulus.

Assemblies of vertical multiwall carbon nanotubes, (VCNTs), have been synthesized by coupling dewetting of cobalt or nickel ultrathin layers and plasma enhanced chemical vapor deposition. Electronic microscopies revealed well defined micrometer length nanotubes with inner radius of 3-4 nm and outer radius of 8-9 nm. Similar structural qualities have been revealed by Raman measurements. Dynamic behaviour of these VCNTs assemblies have been studied by means of Brillouin light scattering technique. The measured inelastic light scattering from VCNTs is attributed to bending vibrations of the nanotubes. The observed frequencies on both assemblies, considered as dense effective media, are compatible with an effective Young modulus of 850 GPa.

Thermodynamics of nanoparticles: experimental protocol based on a comprehensive Ginzburg-Landau interpretation.

The effects of surface and interface on the thermodynamics of small particles require a deeper understanding. This step is crucial for the development of models that can be used for decision-making support to design nanomaterials with original properties. On the basis of experimental results for phase transitions in compressed ZnO nanoparticles, we show the limitations of classical thermodynamics approaches (Gibbs and Landau). We develop a new model based on the Ginzburg-Landau theory that requires the consideration of several terms, such as the interaction between nanoparticles, pressure gradients, defect density, and so on. This phenomenological approach sheds light on the discrepancies in the literature as it identifies several possible parameters that should be taken into account to properly describe the transformations. For the sake of clarity and standardization, we propose an experimental protocol that must be followed during high-pressure investigations of nanoparticles in order to obtain coherent, reliable data that can be used by the scientific community.

Review of the arc process modeling for fullerene and nanotube production.

The arc process remains the easiest and cheapest technique to obtain significant quantities of single wall carbon nanotubes (SWCNTs) with excellent structural properties. These nanotubes are quite straight and present few topological defects. However, the major inconvenience of this process remains the difficult in situ control of the final material's purity and physical properties. The first NASA/Rice workshop on growth mechanisms was devoted to addressing some specific questions on how and where the nanotubes are formed in several processes including the arc. Further advancement requires a detailed understanding of the growth mechanisms of fullerene, nanotubes and soot and their connection with process parameters. This approach is not highly developed today because of the coupling made by non-equilibrium plasma with the nonlinear chemical system makes, in which rate coefficients and reactions are not well known and this makes modeling difficult. This article is an attempt to analyze the effect of the individual arc parameters yielding guidelines for building a mechanistic understanding of carbon based nanomaterial growth in the arc discharge.

Functionalization and extraction of large fullerenes and carbon-coated metal formed during the synthesis of single wall carbon nanotubes by laser oven, direct current arc, and high-pressure carbon monoxide production methods.

Large fullerenes and carbon-coated metal nanoparticles that are formed during the synthesis of carbon nanotubes have been functionalized by the addition of alkyl radicals and isolated by extraction into chloroform. The soluble, functionalized fullerenes have been isolated from raw single-wall carbon nanotube (SWNT) material prepared by laser oven, direct current arc, and high-pressure carbon monoxide production methods. Analyses of the extracted large fullerenes were carried out by thermogravimetric analysis, UV-vis-near-IR, laser desorption ionization mass spectrometry, and high-resolution transmission electron microscopy.

Arc process parameters for single-walled carbon nanotube growth and production: experiments and modeling.

Collarets rich in single-walled carbon nanotubes (SWCNTs) have been grown using a direct current arc method. Arc process parameters such as current, pressure, and anode to cathode distance were varied experimentally and by modeling to provide an optimal working window. The best collaret yields were obtained when helium was used as a buffer gas. Mixing helium with argon in the buffer permits controlling nanotube diameters. In addition to an experimental study, a modeling approach was developed assuming local thermal equilibrium and homogenous and heterogeneous neutral chemistry. The gas-phase chemical model involves 81 neutral carbon species (C1, C2, . . ., C79, C60F, C70F) and 554 reactions with rates taken from data of Krestinin and Moravsky. Axial profiles of temperature, C atom, C2 radical, and fullerene distributions in the reactor are predicted as a function of process parameters. Carbon nanotube growth is considered by a set of surface reactions simulating open nanotube growth. Because nanotube surface chemistry is controlled by the local terminated bond and not by the bulk nanotube bond, a mechanistic approach based on the formal resemblance between the bonding and the structure of open nanotube and other carbon surfaces is proposed to explain nanotube growth. Predicted growth rates are in the range of 100 to 1000 microm/min.