Department of Materials Science, University of Patras, 26504 Rio Patras, Greece, Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vass. Constantinou Avenue, 116 35 Athens, Greece, Institut de Biologie Moleculaire et Cellulaire, UPR9021 CNRS, Immunologie et Chimie Therapeutiques, 67084 Strasbourg, France, and Dipartimento di Scienze Farmaceutiche, Universita di Trieste, Piazzale Europa 1, 34127 Trieste, Italy

Chemistry of Carbon Nanotubes

Fluorescence has been observed directly across the band gap of semiconducting carbon nanotubes. We obtained individual nanotubes, each encased in a cylindrical micelle, by ultrasonically agitating an aqueous dispersion of raw single-walled carbon nanotubes in sodium dodecyl sulfate and then centrifuging to remove tube bundles, ropes, and residual catalyst. Aggregation of nanotubes into bundles otherwise quenches the fluorescence through interactions with metallic tubes and substantially broadens the absorption spectra. At pH less than 5, the absorption and emission spectra of individual nanotubes show evidence of band gap-selective protonation of the side walls of the tube. This protonation is readily reversed by treatment with base or ultraviolet light.

http://science.sciencemag.org/content/sci/297/5581/593.full.pdf

Band gap fluorescence from individual single-walled carbon nanotubes.

Nanotubes from Carbon.

Spectrofluorimetric measurements on single-walled carbon nanotubes (SWNTs) isolated in aqueous surfactant suspensions have revealed distinct electronic absorption and emission transitions for more than 30 different semiconducting nanotube species. By combining these fluorimetric results with resonance Raman data, each optical transition has been mapped to a specific (n,m) nanotube structure. Optical spectroscopy can thereby be used to rapidly determine the detailed composition of bulk SWNT samples, providing distributions in both tube diameter and chiral angle. The measured transition frequencies differ substantially from simple theoretical predictions. These deviations may reflect combinations of trigonal warping and excitonic effects.

/pdf/structure-assigned-optical-spectra-of-single-walled-carbon-4aiapvlgpb.pdf

Structure-Assigned Optical Spectra of Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWNTs) offer the prospect of both new fundamental science and useful (nano)technological applications1. High yields (70–90%) of SWNTs close-packed in bundles can be produced by laser ablation of carbon targets2. 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 SWNTs3,4. 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 production of single-walled carbon nanotubes by the electric-arc technique

Single wall carbon nanotubes (SWNTs) that are found as close-packed arrays in crystalline ropes have been studied by using Raman scattering techniques with laser excitation wavelengths in the range from 514.5 to 1320 nanometers. Numerous Raman peaks were observed and identified with vibrational modes of armchair symmetry (n, n) SWNTs. The Raman spectra are in good agreement with lattice dynamics calculations based on C-C force constants used to fit the two-dimensional, experimental phonon dispersion of a single graphene sheet. Calculated intensities from a nonresonant, bond polarizability model optimized for sp2 carbon are also in qualitative agreement with the Raman data, although a resonant Raman scattering process is also taking place. This resonance results from the one-dimensional quantum confinement of the electrons in the nanotube.

https://science.sciencemag.org/content/sci/275/5297/187.full.pdf

Diameter-Selective Raman Scattering from Vibrational Modes in Carbon Nanotubes

Single-walled carbon nanotubes1 (SWNTs) are predicted to be metallic for certain diameters and pitches of the twisted graphene ribbons that make up their walls2. Chemical doping is expected to substantially increase the density of free charge carriers and thereby enhance the electrical (and thermal) conductivity. Here we use Raman spectroscopy to study the effects of exposing SWNT bundles1 to typical electron-donor (potassium, rubidium) and electron-acceptor (iodine, bromine) dopants. We find that the high-frequency tangential vibrational modes of the carbon atoms in the SWNTs shift substantially to lower (for K, Rb) or higher (for Br2) frequencies. Little change is seen for I2 doping. These shifts provide evidence for charge transfer between the dopants and the nanotubes, indicating an ionic character of the doped samples. This, together with conductivity measurements3, suggests that doping does increase the carrier concentration of the SWNT bundles.

/pdf/evidence-for-charge-transfer-in-doped-carbon-nanotube-324ew52zqd.pdf

Evidence for charge transfer in doped carbon nanotube bundles from Raman scattering

Pulsed laser vaporization of a heated, Fe/Ni or Co/Ni catalyzed, carbon target in argon gas has been used to synthesize single-wall carbon nanotubes (SWNTs). Electron microscopy, x-ray diffraction, and Raman spectroscopy were all used to study the effect of the catalyst on the tube yield, and the evolution of the tube diameter distribution with increasing growth environment temperature $T$. By controlling the temperature in the range $780lTl1050\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, we have been able to tune the diameter of the tubules from $\ensuremath{\sim}0.81$ to $\ensuremath{\sim}1.51\mathrm{nm}$. The threshold temperature for significant SWNT production was found to be $\ensuremath{\sim}850\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$.

Effect of the Growth Temperature on the Diameter Distribution and Chirality of Single-Wall Carbon Nanotubes

A purification procedure for single-wall carbon nanotubes (SWNTs) prepared by pulsed laser ablation is discussed, which separates coexisting carbon nanospheres (CNS), metal nanoparticles, polyaromatic carbons, and fullerenes from the SWNT fraction. The process involves the suspension of CNS, metal nanoparticles, and SWNTs in an aqueous solution using a cationic surfactant and the subsequent trapping of SWNTs on a membrane filter. No oxidative treatment is required. Scanning/transmission electron microscopy and Raman scattering were used to evaluate the purification process and the vibrational features of SWNTs. Purity of SWNTs at the final stage sample is in excess of 90% by weight, and no evidence of impurity carbon phases was revealed in the Raman spectrum of the SWNT fraction.

Purification of single-wall carbon nanotubes by microfiltration

Purification procedures for both multi- (MWNTs) and single-wall carbon nanotubes (SWNTs) are introduced in this paper. Intermediate stages in the purification procedure are monitored by scanning electron microscopy, which clearly shows the increase of the nanotube content with increasing purification. The magnetic properties are investigated by using electron spin resonance (ESR). Two kinds of samples are used in the ESR measurements for MWNTs and for SWNTs. One is dispersed in hexane to make loosely contacting tubules and the other is a dried-deposited tubule to realize a close contacting tubule state. By use of these samples, it is found that the ESR lineshape is closely related to the contact between nanotubes. The curved nature of the tube wall plays an important role in the explanation of the ESR properties.

Shunji Bandow

Papers

Diameter-Selective Raman Scattering from Vibrational Modes in Carbon Nanotubes

Evidence for charge transfer in doped carbon nanotube bundles from Raman scattering

Effect of the Growth Temperature on the Diameter Distribution and Chirality of Single-Wall Carbon Nanotubes

Purification of single-wall carbon nanotubes by microfiltration

Purification and magnetic properties of carbon nanotubes