S. Lefrant

Large-scale production of single-walled carbon nanotubes by the electric-arc technique

Single-walled carbon nanotubes (SWNTs) offer the prospect of both new fundamental science and useful (nano)technological applications. High yields (70–90%) of SWNTs close-packed in bundles can be produced by laser ablation of carbon targets. The electric-arc technique used to generate fullerenes and multi-walled nanotubes is cheaper and easier to implement, but previously has led to only low yields of SWNTs,. Here we show that this technique can generate large quantities of SWNTs with similar characteristics to those obtained by laser ablation. This suggests that the (still unknown) growth mechanism for SWNTs must be independent of the details of the technique used to make them. The ready availability of large amounts of SWNTs, meanwhile, should make them much more accessible for further study.

Large-scale synthesis of single-wall carbon nanotubes by catalytic chemical vapor deposition (CCVD) method

The large-scale production of single-wall carbon nanotubes (SWNTs) is reported. Large quantities of SWNTs can be synthesised by catalytic decomposition of methane over well-dispersed metal particles supported on MgO at 1000°C. The thus produced SWNTs can be separated easily from the support by a simple acidic treatment to obtain a product with high yields (70–80%) of SWNTs. Because the typical synthesis time is 10 min, 1 g of SWNTs can be synthesised per day by this method. The SWNTs are characterized by high-resolution transmission electron microscopy and by Raman spectroscopy, showing the quality and the quantity of products.

Theoretical and experimental vibrational study of emeraldine in salt form. Part II

We present a complete study of the conductive form of the polyaniline emeraldine salt. The experimental spectra of emeraldine salt doped in the classical way and also by the action of camphorsulfonic acid–m-cresol are presented. Vibrational calculations on emeraldine salt are presented, considering the non-planar geometry of the polymer. A study of the influence of the torsion angle between cycles is proposed. Finally, a complete assignment of the Raman vibrational modes of emeraldine salt is discussed. Copyright

SERS spectra of poly(3-hexylthiophene) in oxidized and unoxidized states

Surface enhanced Raman scattering (SERS) is being increasingly used for the study of the structural properties of conducting polymer thin films. It is generally accepted that the enhancement process has an electromagnetic origin, arising from the excitation of surface plasmons in the metal support on which the polymer film is deposited. However, the electromagnetic enhancement is also accompanied by a chemical process, for which available experimental data are scarce. The chemical process originates from the increase in the polarizability of the molecules at the metal surface under the action of the incident radiation, which leads to the formation of new chemical bonds with the atoms of the metal support. The present work was devoted to the study of the SERS spectra of poly(3-hexylthiophene) deposited on rough Ag and Au supports by evaporating the solvent from a solution of known concentration. The experiments revealed the existence of a chemical surface effect. The results obtained show that the SERS spectra depend on the oxidizing properties of the metal surface and on the nature of the solvent. This dependence is explained by the existence of some interfacial reactions that lead to the formation of interface compounds of the type MeX (Me=Ag or Au, X=Cl or O). The SERS measurements reported here reveal an increase in the intensities of the Raman lines, accompanied by a modification of the corresponding intensity ratios, when the degree of doping is increased. It was observed for the first time by SERS spectroscopy that the doping of 3-PHT with FeCl3 leads to the appearance of a state of disorder in the structure of the macromolecular chain, as a result of steric hindrance effects.

Characterization of singlewalled carbon nanotubes-PMMA composites

Thin films of poly(methyl methacrylate)-singlewalled nanotubes (PMMA-SWNTs) composite were produced by spin coating using different nanotubes concentrations. Characterization of these new materials was performed by scanning electron microscopy (SEM) and Raman spectroscopy in order to obtain information on the possible interactions between these two materials and especially, on the modifications of the nanotubes and their organization. It is found that in the composite films, the distance between the nanotubes in bundles increases because of the intercalation of polymer. For low nanotube concentrations, amorphous carbon is dispersed in the polymer matrix giving more uniform thin films.

Transport properties of PMMA-Carbon Nanotubes Composites

We report transport measurements on PMMA-singlewalled carbon nanotubes composites films. The films are characterized by Raman spectroscopy, optical absorption and electron microscopy. At room temperature, classical percolation theory applies. It shows that the composites resistivity is indeed controlled by the nanotubes. Decreasing the temperature shows a unusual behavior which suggests that a distribution of intertube/interbundle barriers of some 10 of Kelvin is superposed to the topological percolation problem.

SERS spectra of polyaniline thin films deposited on rough Ag, Au and Cu. Polymer film thickness and roughness parameter dependence of SERS spectra

Abstract Surface-enhanced Raman scattering (SERS) has lately proved to be an effective technique which has led to its increasing application for studying the structural properties of conducting polymer thin films. It is generally accepted that the enhancement process has an electromagnetic origin arising from the excitation of surface plasmons (SPs) in the metal support on which the polymer film is deposited. However, the electromagnetic enhancement is also accompanied by a chemical process, on which only scarce experimental data are available at present. The chemical process originates in an increased polarizability of the molecules at the metal surface under the action of an incident radiation, as a result of which new chemical bonds are formed with the atoms of the metal support. This paper is devoted to the study of the SERS spectra under 1064 nm excitation for two forms of polyaniline, one of the emeraldine base type and the other of the emeraldine salt type. Our purpose has been to identify the chemical effects at the polymer/metal interface that are involved in specific modifications of the SERS spectra. The following results concerning SERS spectrum variation with metal support type (Ag, Au and Cu) have been obtained. An oxidation of emeraldine base taking place at the polymer/metal interface has been revealed. In the case of emeraldine salt, an oxidized form of polyaniline, the SERS spectra remain unchanged regardless of the changes in the metal support, which proves the stability of this form. A new result has been obtained as SERS spectroscopy revealed an electron delocalization process taking place in the emeraldine salt molecule as a result of an electron transfer from metal to the polymer molecule occurring on the level of quinoid rings. The concept of a rough Raman-active surface has been clarified by using a parameter h a , similar to the grating groove depth/grating periodicity ratio which occurs when a diffraction grating is used as optic coupler.

Evolution and evaluation of the polymer/nanotube composite

Abstract Composite structures, using MWNT and SWNT and the polymer (PmPV) exhibit properties which enhance those of the individual components. The polymer PmPV can act as an organic filter for the multiwalled system where the MWNT are indefinitely suspended in the polymer solution while the carbonaceous material falls out of solution. Raman measurements of this show a complete reduction of the amorphous line at 1350 cm-1. We see that we can alter the luminescence quantum yield of the composite, where the effects are different depending on which nanotubes are used. When we examine the SWNT/PmPV the quantum yield is increased. The MWNT composite also shows strong non-linear optical signal. The pristine polymer has an χ (3) of 10 −11 esu whereas the composite χ (3) is -10 −10 esu.

Raman studies on single walled carbon nanotubes produced by the electric arc technique

Carbon single walled nanotubes (SWNTs) have been produced in high yields using the electric arc technique. TEM studies show that the SWNTs have a narrow diameter distribution around an average value of 1.3 nm. In this paper, we focus on the characterization of these samples by high resolution Raman spectroscopy (HRRS). The presence of large amounts of SWNTs in the samples induces a very rich structure in the Raman spectra, typical for this class of carbonaceous material. Armchair tubes with (8,8) to (12,12) geometry can be detected, in agreement with the narrow diameter distribution observed by TEM measurements. The ability of HRRS as a highly sensitive fingerprint technique in identifying SWNTs with different diameters and geometries is discussed.

Characterization of multiwalled carbon nanotubes-PMMA composites

We report, for the first time, preliminary results obtained from analysis of poly(methyl methacrylate) -multiwalled carbon nanotubes composites thin films. These films were prepared by mixing the polymer with different nanotube concentrations and were deposited by spin coating on glass substrates. The composites were characterized by Raman spectroscopy and scanning electron microscopy. The evolution of the conductivity versus the nanotube concentration was carried out in the order to determine the transport process in these materials. Such a composite is promising for use as transporting layer in multilayer diodes.