Showing papers by "James Hone published in 2000"
TL;DR: In this article, the authors show that the electrical resistivity exhibits moderate anisotropy with respect to the alignment axis, while the thermopower is the same when measured parallel or perpendicular to this axis.
Abstract: Dense, thick films of aligned single wall carbon nanotubes and nanotube ropes have been produced by filtration/deposition from suspension in strong magnetic fields. Electrical resistivity exhibits moderate anisotropy with respect to the alignment axis, while the thermopower is the same when measured parallel or perpendicular to this axis. Both parameters have identical temperature dependencies in the two orientations. Thermal conductivity in the parallel direction exceeds 200 W/mK, within a decade of graphite.
850 citations
TL;DR: The data show direct evidence of one-dimensional quantized phonon subbands above 4 kelvin, in excellent agreement with model calculations of individual nanotubes and differ markedly from the specific heat of two-dimensional graphene or three-dimensional graphite.
Abstract: The electronic spectra of carbon nanotubes and other nanoscale systems are quantized because of their small radii. Similar quantization in the phonon spectra has been difficult to observe because of the far smaller energy scale. We probed this regime by measuring the temperature-dependent specific heat of purified single-wall nanotubes. The data show direct evidence of one-dimensional quantized phonon subbands. Above 4 kelvin, they are in excellent agreement with model calculations of individual nanotubes and differ markedly from the specific heat of two-dimensional graphene or three-dimensional graphite. Detailed modeling yields an energy of 4.3 millielectron volts for the lowest quantized phonon subband and a tube-tube (or “lattice”) Debye energy of 1.1 millielectron volts, implying a small intertube coupling in bundles.
465 citations
TL;DR: The thermoelectric power (TEP) of single-walled carbon nanotubes (SWNTs) is extremely sensitive to gas exposure history, leading to apparently "variable" TEP for a given sample at a given temperature.
Abstract: The thermoelectric power (TEP) of single-walled carbon nanotubes (SWNTs) is extremely sensitive to gas exposure history. Samples exposed to air or oxygen have an always positive TEP, suggestive of holelike carriers. However, at fixed temperature the TEP crosses zero and becomes progressively more negative as the SWNTs are stripped of oxygen. The time constant for oxygen adsorption/desorption is strongly temperature dependent and ranges from seconds to many days, leading to apparently "variable" TEP for a given sample at a given temperature. The saturated TEP can be accounted for within a model of strong oxygen doping of the semiconducting nanotubes.
215 citations
TL;DR: In this article, the effects of potassium doping on the conductance of individual semiconducting single-walled carbon nanotube ropes were investigated. But the results were limited to a single-dimensional graph.
Abstract: We report the effects of potassium doping on the conductance of individual semiconducting single-walled carbon nanotube ropes. We are able to control the level of doping by reversibly intercalating and de-intercalating potassium. Potassium doping changes the carriers in the ropes from holes to electrons. Typical values for the carrier density are found to be ∼100–1000 electrons/μm. The effective mobility for the electrons is μeff∼20–60 cm2 V-1 s-1, a value similar to that reported for the hole effective mobility in nanotubes [R. Martel et al., Appl. Phys. Lett. 73, 2447 (1998)].
170 citations
TL;DR: In this article, an individual single-wall carbon nanotube rope before and after doping in situ with potassium was reported, and all the features in R(T) were qualitatively reproduced by the rope data.
Abstract: Four-probe resistance vs temperature and gate voltage are reported for an individual single-wall carbon nanotube rope before and after doping in situ with potassium. All the features in R(T) from unoriented bulk material, before and after doping, are qualitatively reproduced by the rope data. The 5.3 K conductance of the pristine rope decreases with positive gate voltage, while G vs V{sub g} becomes featureless after K doping. (c) 2000 The American Physical Society.
84 citations
TL;DR: The data support the view that the conduction electron density is concentrated at the C60 "equator," away from the interfullerene bonds.
Abstract: We present high resolution ${}^{133}\mathrm{Cs}{\ensuremath{-}}^{13}\mathrm{C}$ double resonance NMR data and ${}^{13}\mathrm{C}{\ensuremath{-}}^{13}\mathrm{C}$ NMR correlation spectra of ${}^{13}\mathrm{C}$ enriched samples of the polymeric phase of ${\mathrm{CsC}}_{60}$. These data lead to a partial assignment of the lines in the ${}^{13}\mathrm{C}$ NMR spectrum of ${\mathrm{CsC}}_{60}$ to the carbon positions on the ${\mathrm{C}}_{60}$ molecule. A plausible completion of the assignment can be made on the basis of an ab initio calculation. The data support the view that the conduction electron density is concentrated at the ${\mathrm{C}}_{60}$ ``equator,'' away from the interfullerene bonds.
17 citations
TL;DR: The thermal properties of carbon nanotubes are strongly dependent on their unique structure and size, and show promise as an ideal material for thermal management on the micro and macro-scale as discussed by the authors.
Abstract: The thermal properties of carbon nanotubes are strongly dependent on their unique structure and size, and show promise as an ideal material for thermal management on the micro- and macro-scale. The specific heat of nanotubes is similar to that of two-dimensional graphene at high temperatures, but is sensitive to the effects of rolling the the graphene sheet into a small cylinder at low temperatures. Specifically, the acoustic phonon modes are stiffened due to the cylindrical geometry, and the phonon spectrum is quantized due to the small diameter of the tube. In bundles of single-walled nanotubes, the specific heat is a sensitive probe of inter-tube mechanical coupling. Measurements of the specific heat show that inter-tube coupling is relatively weak, and show direct evidence for quantum effects. The thermal conductivity of nanotubes should reflect the on-tube phonon structure. Aligned bundles of SWNTs show a high thermal conductivity (>200 W/m-K at room temperature), and possible quantization effects at low temperature.
6 citations