Eric Anglaret

Production of high-density single-walled nanotube material by a simple laser-ablation method

Abstract A continuous-wave 250 W CO2-laser operating at 10.6 μm has been employed to evaporate graphite/bi-metal targets in a vertical evaporation chamber. Without the help of an additional furnace, web-like soot material has been easily produced. This contains high densities of bundles of single-walled nanotubes (SWNTs). Electron microscopy, Raman spectroscopy and neutron diffraction show the high quality of the SWNT material. The use of this simple laser-ablation system offers additional possibilities to study experimental parameters important for the formation of SWNTs leading to a better understanding of its growth mechanism.

Resonant Raman study of the structure and electronic properties of single-wall carbon nanotubes

We investigate the laser-energy dependence of the Raman profile of single-wall carbon nanotube (SWNT) samples with various distributions of diameters. We show that resonant Raman is an efficient tool for the study of the structure and electronic properties of SWNT. The tube diameter distribution is derived from the comparison between the experimental frequencies of the radial A1g breathing mode range (RBM) and the calculated RBM frequency of SWNT bundles. Metallic or semi-conducting tubes are identified in the light of calculations of allowed optical transitions. The assignments are confirmed by the observation (absence) of a Breit–Wigner–Fano-like lineshape for the tangential graphite-like modes of metallic (semiconducting) nanotubes.

Carbon nanotubes for optical limiting

This paper reviews the optical limiting properties of carbon nanotubes. The nonlinear optical properties of nanotubes were investigated in water and in chloroform suspensions. Nonlinear transmittance measurements were reported for various pulse durations and wavelengths and show that carbon nanotubes are good candidates for effective optical limiting over broad temporal and laser energy ranges. Z-Scans and pump-probe time-resolved experiments were achieved to identify the origin of optical limiting in nanotubes. The main phenomenon is a strong nonlinear scattering, originating from solvent vapour bubble growth and sublimation of nanotubes at high fluences. Heat transfer from particles to solvent is particularly effective as compared to carbon black suspensions because of the large surface area of the carbon nanotubes.

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.

Phonons in single wall carbon nanotube bundles

Abstract We review recent and original results on the vibrational properties of single wall carbon nanotubes (SWNT). We especially focus on calculations and experiments performed on nanotube bundles. So far, the main technique for probing the dynamics has been Raman spectroscopy. Here, we discuss: (i) the relation between frequency of the A 1 g radial breathing mode and nanotube diameter, (ii) the origin of resonance and the consequences on the profile and intensity of the Raman lines, and (iii) the assignment and resonant behaviour of the Raman lines between 700 and 1000 cm −1 . Recently, inelastic neutron scattering techniques (INS) were shown to be effective tools to probe the vibrational density of states of SWNT. We review the INS results and focus on the study of low frequency excitations, especially libration-twist modes and acoustic modes. Both Raman and INS results are analysed in the light of calculations performed in a valence force field model taking into account van der Waals intertubes interactions in the bundles.

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.

Self-Deactivation of Single-Walled Carbon Nanotube Growth Studied by in Situ Raman Measurements

In situ Raman measurements were used to investigate the kinetics and the self-deactivation of the growth of single-walled carbon nanotubes during catalytic chemical vapor deposition. The kinetics appear controlled by the mass-transport of the gaseous precursor at low precursor pressure and high temperature and by the catalytic decomposition of the precursor at high precursor pressure and low temperature. The initial growth rate and the lifetime display inversely correlated evolutions with the growth parameters. In addition, we measured the activation energy for the healing of defects during the growth and discuss it in comparison to the apparent activation energies measured for the initial growth rate and the lifetime. Our results support that the healing of the edge defects controls both the crystalline order and the growth lifetime.

Anisotropic Thin Films of Single-Wall Carbon Nanotubes from Aligned Lyotropic Nematic Suspensions

Lyotropic nematic aqueous suspensions of single-wall carbon nanotubes can be uniformly aligned in thin cells by shearing. Homogeneous anisotropic thin films of nanotubes can be prepared by drying the nematic. Optical transmission between parallel or crossed polarizers is measured and described in order to estimate the dichroic ratio. The order parameter is measured using polarized Raman spectroscopy and found to be quite weak due to entanglement of the nanotubes and/or to an intrinsic viscoelastic behavior of the nanotube suspensions.

Pulse duration and wavelength effects on the optical limiting behavior of carbon nanotube suspensions

We investigate pulse duration and wavelength effects on the optical limiting behavior of single-wall carbon nanotubes suspended either in chloroform or in water. The principal optical limiting effect in carbon nanotube suspensions is nonlinear scattering that is due to heat transfer from particles to solvent, leading to solvent-bubble formation and to sublimation of carbon nanotubes. We report on nonlinear transmittance measurements for pulse durations ranging from 3 to 100 ns and for wavelengths from 430 to 1064 nm. The dependence of optical limiting behavior on pulse duration and wavelength is analyzed and discussed in terms of nonlinear mechanisms.

Processes Controlling the Diameter Distribution of Single-Walled Carbon Nanotubes during Catalytic Chemical Vapor Deposition

Single-walled carbon nanotubes are grown by catalytic chemical vapor deposition in various conditions of temperature and carbon precursor pressure. Systematic analyses of the Raman radial breathing modes at two laser wavelengths are used to monitor the evolution of the diameter distribution. Two distinct domains with opposite influences of the temperature and the precursor pressure on the diameter distribution are evidenced. Thanks to specially designed experiments made of two successive growths, three processes are identified to influence the diameter distribution during the nanotube growth: (i) at too low precursor pressure, nanotube nucleation cannot occur on the smallest catalyst particles; (ii) at low temperature and high precursor pressure, small catalyst particles are preferably encapsulated by disordered carbon structures; (iii) at high temperature, catalyst coarsening causes the disappearance of the smallest catalyst particles.