C. Journet

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.

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.

TUNING AND MONITORING THE ELECTRONIC STRUCTURE OF CARBON NANOTUBES

Abstract The possibility of tuning the Fermi level of single-wall carbon nanotubes by exposure to molecules of different redox potentials allows for selectively filling or depleting their density of states and thus modifying the conducting nature of the individual tubes. The modifications of the electronic bands that occur upon charge transfer are probed by optical absorption spectroscopy performed on thin films.

SINGLE-WALL CARBON NANOTUBES FOR OPTICAL LIMITING

Abstract We report on the non-linear optical transmittance of single-wall carbon nanotubes (SWNT) in a water/surfactant suspension. Optical limiting is observed at low-energy thresholds both in the visible and near-infrared. We find small non-linear thresholds and large optical densities that match or overpass the performances of other good optical limiters (C60 and carbon black) both in the visible and in the near-infrared, which makes SWNT very promising systems for broadband optical limiting.

Purification procedure of carbon nanotubes

We report results on purification and characterization of single wall carbon nanotubes prepared by the electric arc method. The process consists of a chemical treatment based on a reflux with nitric acid followed by successive filtration steps (tangential flow and frontal filtration) of a suspension of the raw material. The effects of each step are analysed by SEM and TEM.

Optical limiting properties of singlewall carbon nanotubes

We report on the optical limiting performances of singlewall carbon nanotubes. The nonlinear transmission of the samples is investigated using nanosecond Nd:YAG laser pulses at 532 nm and 1064 nm. Z-scan experiments are carried out at different incident energies in order to identify the effects responsible for nonlinear transmission. We find that nonlinear scattering and nonlinear refraction are the dominant mechanisms. Optical limiting efficiencies are compared with those of multiwall nanotubes, carbon black suspensions and fullerenes.

Coalescence of single-walled carbon nanotubes and formation of multi-walled carbon nanotubes under high-temperature treatments

Electric arc-discharge single-wall carbon nanotubes are annealed between 1600 and 2800 °C under argon flow. Their stability and evolution are studied by coupling TEM, X-ray diffraction and Raman spectroscopy. The first modifications appear at 1800 °C with a significant decrease of the crystalline order. It is due to SWNTs coalescence leading to smaller bundles but with an increase of the tube diameters from 2 to 4 nm. From 2200 °C, SWNTs progressively disappear to the benefit of MWNTs having at first two to three carbon layers then reaching 7 nm external diameter. The possible mechanisms responsible for the SWNTs coalescence and instability and their transformation in MWNTs are discussed.

Single-electron transistor made of multiwalled carbon nanotube using scanning probe manipulation

We positioned semiconducting multiwalled carbon nanotube, using an atomic force microscope, between two gold electrodes at SiO2 surface. Transport measurements exhibit single-electron effects with a charging energy of 24 K. Using the Coulomb staircase model, the capacitances and resistances between the tube and the electrodes can be characterized in detail.

Acoustoelectric Effects in Carbon Nanotubes

We show that it is possible to detect mechanical bending modes on 1µm long ropes of single walled-carbon nanotubes suspended between 2 metallic contacts. This is done by measuring either their dc resistance in a region of strong temperature dependence (in the vicinity of superconducting or metal-insulator transition), or their critical current. The vibrations are excited by a radio-frequency electric field produced by an antenna located in the vicinity of the sample. We analyze the mechanism of detection of the mechanical resonances in terms of heating and phase breaking effects.

Raman characterization of singlewalled carbon nanotubes and PMMA-nanotubes composites

The Raman spectroscopy have allowed us to perform studies on singlewalled nanotubes (SWNTs) produced by following methods: electric arc, laser ablation and solar energy. As this characterization method provides a great deal of informations, we will present a comparison between the nanotubes produced by all these processes and the influence of some synthesis parameters. By using spin casting, we have produced thin films of PMMA-SWNTs for different concentrations. Then, we have characterized these new materials by Raman spectroscopy. The aim of these investigations is to get information on the possible interactions between these two materials. In particular, we have studied the evolution of the composites films spectra as a function of the nanotubes concentration in the polymer.