702 research outputs found
Meta- and hybrid-CNTs: A clue for the future development of carbon nanotubes
A new generation of carbon nanotubes (CNTs), which may be named âmeta-nanotubesâ, is more and more the focus of the research worldwide. They result from the transformation of âregularâ CNTs by various ways such as functionalisation, doping, substitution, etc. The new nanomaterials thereby created are likely to exhibit new behaviors, specifically regarding properties that pristine CNTs do not possess (reactivity, solubility, magnetismâŠ). The paper includes the description of the various routes to synthesize hybrid CNTs and their related advantages and limitations, while providing examples of the resulting materials from both literature and authorâs team work. Hybrid SWNTs (abbreviated as X@SWNTs) are one example of meta-nanotubes, and consist in SWNTs whose the hollow core is fully or partially filled with foreign atoms, molecules, or compounds. The inserted material may then exhibit a peculiar behavior with respect to the macroscopic state, for several non-exclusive reasons: 1D-dimension preventing electron scattering and enhancing the role of surface atoms, protection from surface adsorption of disturbing molecules by the carbon sheath, anisotropic lattice distortion or creation of new structures due to imposed dimensions, interactions/electron coupling with the surrounding carbon lattice. A wide field is thus open, possibly even wider than for pristine SWNTs
Gate-tuned high frequency response of carbon nanotube Josephson junctions
Carbon nanotube (CNT) Josephson junctions in the open quantum dot limit
exhibit superconducting switching currents which can be controlled with a gate
electrode. Shapiro voltage steps can be observed under radiofrequency current
excitations, with a damping of the phase dynamics that strongly depends on the
gate voltage. These measurements are described by a standard RCSJ model showing
that the switching currents from the superconducting to the normal state are
close to the critical current of the junction. The effective dynamical
capacitance of the nanotube junction is found to be strongly gate-dependent,
suggesting a diffusive contact of the nanotube.Comment: 14 pages, 8 figure
X-ray diffraction as a tool for the determination of the structure of double-walled carbon nanotube batches
The average structure of double-walled carbon nanotube DWCNT samples can be determined by x-ray diffraction XRD. We present a formalism that allows XRD patterns of DWCNTs to be simulated and we give researchers the tools needed to perform these calculations themselves. Simulations of XRD patterns within this formalism are compared to experimental data obtained on two different DWCNT samples, produced by chemical vapor deposition or by peapod conversion i.e., high-temperature peapod annealing. For each sample, we are able to determine structural aspects such as the number of walls, the diameter distribution of inner and outer tubes, the intertube spacing, and the bundled structure
Fluidized bed chemical vapor deposition of copper nanoparticles on multiwalled carbon nanotubes
Multi-walled carbon nanotubes tangled in easy-to-fluidize porous balls have been decorated by pure copper nanoparticles using a pre-industrial fluidized bed chemical vapor deposition process. Copper (II) acetylacetonate Cu(acac)2 was used as precursor. The low precursor volatility led to low deposition rates, responsible for a nonuniformity of the deposit both on the MWCNT balls and from the outer part to the center of the balls. An oxidative pre-treatment of the MWCNTs allowed to increase slightly the deposit weight and uniformity, by creating new nucleation sites on the nanotube surface. It also allowed decreasing the size of Cu nanoparticles by a factor of ten. A decrease of the deposition temperature increased more markedly the deposit weight, by probably favoring the formation of gaseous reactive intermediate species more reactive on the oxidized nanotube surface. A more efficient precursor delivery system would allow reaching higher deposition rates and much more uniform deposits, making possible an industrial production of metallized carbon nanotube
Ultraviolet photon absorption in single- and double-wall carbon nanotubes and peapods: Heating-induced phonon line broadening, wall coupling, and transformation
Ultraviolet photon absorption has been used to heat single- and double-wall carbon nanotubes and peapods in vacuum. By increasing the laser intensity up to 500 mW, a downshift and a broadening of the optical phonons are observed corresponding to a temperature of 1000°C. The UV Raman measurements are free of blackbody radiation. We find that the linewidth changes for the G+ and Gâ bands differ considerably in single-wall carbon nanotubes. This gives evidence that the phonon decay process is different in axial and radial tube directions. We observe the same intrinsic linewidths of graphite (highly oriented pyrolytic graphite) for the G band in single- and double-wall carbon nanotubes. With increasing temperature, the interaction between the walls is modified for double-wall carbon nanotubes. Ultraviolet photon induced transformations of peapods are found to be different on silica and diamond substrates
Transport via coupled states in a C60 peapod quantum dot
We have measured systematic repetitions of avoided crossings in low
temperature three-terminal transport through a carbon nanotube with
encapsulated C60 molecules. We show that this is a general effect of the
hybridization of a host quantum dot with an impurity. The well-defined nanotube
allows identification of the properties of the impurity, which we suggest to be
a chain of C60 molecules inside the nanotube. This electronic coupling between
the two subsystems opens the interesting and potentially useful possibility of
contacting the encapsulated molecules via the tube.Comment: 6 pages, 3 figure
Encapsulating C59N azafullerene derivatives inside single-wall carbon nanotubes
Filling of single-wall carbon nanotubes with C59N azafullerene derivatives is
reported from toluene solvent at ambient temperature. The filling is
characterized by high resolution transmission electron microscopy and Raman
spectroscopy. The filling efficiency is the same as for C60 fullerenes and the
tube-azafullerene interaction is similar to the tube-C60 interaction. Vacuum
annealing of the encapsulated azafullerene results in the growth of inner
tubes, however no spectroscopic signature of nitrogen built in the inner walls
is detected.Comment: To appear in Carbo
High pressure water pyrolysis of coal to evaluate the role of pressure on hydrocarbon generation and source rock maturation at high maturities under geological conditions
This study investigates the effect of water pressure on hydrocarbon generation and source rock maturation at high maturities for a perhydrous Tertiary Arctic coal, Svalbard. Using a 25 ml Hastalloy vessel, the coal was pyrolysed under low water pressure (230â300 bar) and high water pressure (500, 700 and 900 bar) conditions between 380 °C and 420 °C for 24 h. At 380 °C and 420 °C, gas yields were not affected by pressure up to 700 bar, but were reduced slightly at 900 bar. At 380 °C, the expelled oil yield was highest at 230 bar, but reduced significantly at 900 bar. At 420 °C cracking of expelled oil to gas was retarded at 700 and 900 bar. As well as direct cracking of the coal, the main source of gas generation at high pressure at both 380 °C and 420 °C is from bitumen trapped in the coal, indicating that this is a key mechanism in high pressure geological basins. Vitrinite reflectance (VR) was reduced by 0.16 %Ro at 380 °C and by 0.27 %Ro at 420 °C at 900 bar compared to the low pressure runs, indicating that source rock maturation will be more retarded at higher maturities in high pressure geological basins
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