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.
Degassing of bundles of single-walled carbon nanotubes in vacuum at 500 K is found to drive the thermoelectricpower (TEP) strongly negative, indicating that the degassed metallic tubes in a bundle are n type. The magnitude of the negative TEP indicates that important asymmetry in the electronic carbon pi bands exists near the Fermi energy. Easily measurable increases in the TEP ( approximately 5-10 &mgr;V/K) and resistivity ( 2%-10%) are observed at 500 K upon exposure to N2 and He, suggesting that even gas collisions with the nanotube wall can contribute significantly to the transport properties.
We report intercalation of charged polyiodide chains into the interstitial channels in a singlewall carbon nanotube (SWNT) rope lattice, suggesting a new carbon chemistry for nanotubes, distinctly different from that of graphite and C 60 . This structural model is supported by results from Raman spectroscopy, x-ray diffraction, Z-contrast electron microscopy, and electrical transport data. Iodine-doped SWNTs are found to be air stable, permitting the use of a variety of techniques to explore the effect of charge transfer on the physical properties of these novel quantum wires.[S0031-9007(98)
Carbon materials, with their diverse
allotropes, have played significant
roles in our daily life and the development of material science. Following
0D C60 and 1D carbon nanotube, 2D graphene materials, with
their distinctively fascinating properties, have been receiving tremendous
attention since 2004. To fulfill the efficient utilization of 2D graphene
sheets in applications such as energy storage and conversion, electrochemical
catalysis, and environmental remediation, 3D structures constructed
by graphene sheets have been attempted over the past decade, giving
birth to a new generation of graphene materials called 3D graphene
materials. This review starts with the definition, classifications,
brief history, and basic synthesis chemistries of 3D graphene materials.
Then a critical discussion on the design considerations of 3D graphene
materials for diverse applications is provided. Subsequently, after
emphasizing the importance of normalized property characterization
for the 3D structures, approaches for 3D graphene material synthesis
from three major types of carbon sources (GO, hydrocarbons and inorganic
carbon compounds) based on GO chemistry, hydrocarbon chemistry, and
new alkali-metal chemistry, respectively, are comprehensively reviewed
with a focus on their synthesis mechanisms, controllable aspects,
and scalability. At last, current challenges and future perspectives
for the development of 3D graphene materials are addressed.
We have subjected single-walled carbon nanotube materials (SWNTM's) to a variety of organic functionalization reactions. These reactions include radioactive photolabeling studies using diradical and nitrene sources, and treatment with dichlorocarbene and Birch reduction conditions. All of the reactions provide evidence for chemical attachment to the SWNTM's, but because of the impure nature of the staring materials, we are unable to ascertain the site of reaction. In the case of dichlorocarbene we are able to show the presence of chlorine in the SWNT bundles, but as a result of the large amount of amorphous carbon that is attached to the tube walls, we cannot distinguish between attachment of dichlorocarbene to the walls of the SWNT's and reaction with the amorphous carbon.
Electrochemical doping of bisulfate ions into single wall carbon nanotube (SWNT) bundles has been studied
using coulometry, cyclic voltammetry, mass-uptake measurements, and Raman scattering experiments. A
spontaneous charge-transfer reaction is observed prior to the application of an electrochemical driving force,
in sharp contrast to previous observations in the graphite−H2SO4 system. A mass increase of the SWNT
sample and a concomitant upshift of the Raman-active tangential mode frequency indicate oxidation (i.e.,
removal of electrons) of the SWNT bundles. In fact, using Raman scattering, we were able to separate the
spontaneous and electrochemical contributions to the overall charge transfer, resulting in the value of an
upshift of 320 cm-1 per hole, per C-atom introduced into the carbon π-band by the bisulfate (HSO4
-) dopant.
This value may prove to be a universal measure of charge transfer in acceptor-type SWNT compounds. At
a critical electrochemical doping, the SWNT bundles are driven into an “overoxidation” regime, where they
are irreversibly oxidized with the formation of C−O covalent bonds, analogous to electrochemical formation
of graphite oxides.
The electrical transport properties of single-wall carbon nanotubes are shown to be strongly influenced by the presence of transition-metal impurities derived from the catalyst introduced to stimulate their growth. Data on thermoelectric power and electrical resistance in the temperature range 10-400 K were obtained on a series of samples prepared using MY catalysts ͑M ϭCr, Mn, Co, Fe, Ni͒. The unusual transport behavior observed is tentatively assigned to an interaction between the magnetic moment of the M atom and the spin of the conduction electrons of the nanotubes, i.e., the Kondo effect. ͓S0163-1829͑99͒50240-3͔ RAPID COMMUNICATIONS R11 312 PRB 60 L. GRIGORIAN et al.
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