High-field electrical transport in single-wall carbon nanotubes

Using low-resistance electrical contacts, we have measured the intrinsic high-field transport properties of metallic single-wall carbon nanotubes. Individual nanotubes appear to be able to carry currents with a density exceeding 10(9) A/cm(2). As the bias voltage is increased, the conductance drops dramatically due to scattering of electrons. We show that the current-voltage characteristics can be explained by considering optical or zone-boundary phonon emission as the dominant scattering mechanism at high field.     

High-field electron emission of carbon nanotubes grown on carbon fibers

Carbon nanotubes with uniform density were synthesized on carbon fiber substrate by the floating catalyst method. The morphology and microstructure were characterized by scanning electron microscopy and Raman spectroscopy. The results of field emission showed that the emission current density of carbon nanotubes/carbon fibers was 10 μA/cm² and 1 mA/cm² at the field of 1.25 and 2.25 V/μm, respectively, and the emission current density could be 10 and 81.2 mA/cm² with the field of 4.5 and 7 V/μm, respectively. Using uniform and sparse density distribution of carbon nanotubes on carbon fiber substrate, the tip predominance of carbon nanotubes can be exerted, and simultaneously the effect of screening between adjacent carbon nanotubes on field emission performance can also be effectively decreased. Therefore, the carbon nanotubes/carbon fibers composite should be a good candidate for a cold cathode material.     

Quantum-dot transport in carbon nanotubes

Transport measurements on a bundle of single-walled carbon nanotubes have been made below 4.2 K as a function of side gate and source–drain bias voltage. The transport of an individual nanotube is described by the Coulomb blockade effect. The zero-dimensional quantum states of the nanotube become clear for measurements of large bias voltage. In addition, we present preliminary results of microwave application to the SWNT dot, and the results can be qualitatively explained by classical coupling to the dot.     

Spin-polarized transport in carbon nanotubes

We present transport measurements of ferromagnetically contacted carbon nanotubes. In both single- and multi-walled nanotube devices, a spin valve effect is observed due to spin-polarized transport. In one single-walled nanotube device, the spin-valve effect is suppressed as the influence of Coulomb charging is observed at around 10 K. To help understand the interplay between the Coulomb charging and the spin-polarized transport we investigated the temperature dependence of the carbon nanotube magnetoresistance.     

Correlated transport in carbon nanotubes

The low-energy theory for single-wall armchair carbon nanotubes including Coulomb interactions is given. It describes two fermion chains without interchain hopping but coupled in a specific way by the interaction. The strong-coupling properties are studied by bosonization, and the consequences for experiments on single armchair nanotubes are discussed.     

Quantum transport in carbon nanotubes

A survey will be given on selected experiments showing evidence of quantum transport in carbon nanotubes. The phenomena involve electron confinement, single electron effects and Coulomb–Blockade, Kondo-physics, conductance quantisation, Aharonov–Bohm effect, phase breaking in ballistic transport, and magnetochiral anisotropy.     

Electronic transport in Y-junction carbon nanotubes

Electronic transport measurements were performed on Y-junction carbon nanotubes. These novel junctions contain a large diameter tube branched into smaller ones. Independent measurements using good quality contacts on both individual Y junctions and many in parallel show intrinsic nonlinear transport and reproducible rectifying behavior at room temperature. The results were modeled using classic interface physics for a junction with an abrupt change in band gap due to the change in tube diameter. These Y-junction tubes represent new heterojunctions for nanoelectronics.     

Electron transport in double-walled carbon nanotubes

The transport properties of finite length double-walled carbon nanotubes subject to the influences of a transverse electric field and a magnetic field with varying polar angles are investigated theoretically. The electrical conductance, thermal conductance and Peltier coefficient dependences on the external fields and symmetric configuration are studied in linear response regime. Prominent peak structures of the electrical conductance are predicted when varying the electric field strength. The features of the conductance peaks are found to be strongly dependent on the external fields and the intertube interactions. The heights of the electrical and thermal conductance peaks display the quantized behavior, while those of the Peltier coefficient do not. The conductance peaks are found to be broadened by the finite temperature.     

On ballistic transport in carbon nanotubes

We investigate theoretically the ballistic regime exhibited by conduction electrons in multiwalled carbon nanotubes in relation to the conductance quantization in these tubes. Starting from the fact that electron drift mobility is quantized in multiwall tubes, essential aspects related to both ballistic and diffusive regimes are discussed.     

Surface-charge-governed electrolyte transport in carbon nanotubes

The transport behavior of pressure-driven aqueous electrolyte solution through charged carbon nanotubes(CNTs) is studied by using molecular dynamics simulations. The results reveal that the presence of charges around the nanotube can remarkably reduce the flow velocity as well as the slip length of the aqueous solution, and the decreasing of magnitude depends on the number of surface charges and distribution. With 1-M KCl solution inside the carbon nanotube, the slip length decreases from 110 nm to only 14 nm when the number of surface charges increases from 0 to 12 e. This phenomenon is attributed to the increase of the solid–liquid friction force due to the electrostatic interaction between the charges and the electrolyte particles, which can impede the transports of water molecules and electrolyte ions. With the simulation results,we estimate the energy conversion efficiency of nanofluidic battery based on CNTs, and find that the highest efficiency is only around 30% but not 60% as expected in previous work.     

多壁碳纳米管中的多通道弹道输运特性

借助于扫描电子显微镜中可移动金属探针的测量系统,实现了探针电极与W衬底上生长的单根多壁碳纳米管一端的完美接触.研究了单根多壁碳纳米管室温下的电输运特性,发现多壁碳纳米管具有非常高的电流承载能力.对于直径100nm的碳纳米管,其电阻为34.4Ω,流经碳纳米管的最大电流可达7.27 mA,对应的电导为 460—490G0 .这一实验结果表明,大直径的多壁碳纳米管在室温下可以实现多通道弹道输运,是未来纳电子器件与电路的理想互联导线.     

Multichannel ballistic transport in multiwall carbon nanotubes

The electric transport properties of an individual vertical multiwall carbon nanotube (MWCNT) were studied in situ at room temperature in a scanning electron microscope chamber. It was found that the single MWCNT has a large current-carrying capacity, and the maximum current can reach 7.27 mA. At the same time, a very low resistance of about 34.4 ohms and a high conductance of about (460-490)G0 were obtained. The experimental observations imply a multichannel quasiballistic conducting behavior occurring in the MWCNTs with large diameter, which can be attributed to the participation of multiple walls in electrical transport and the large diameter of the MWCNTs.     

Spin-polarized transport in carbon nanotubes with impurities

Impurity effects on the spin-polarized transport through armchair carbon nanotubes contacted by ferromagnetic leads are investigated theoretically. The length of the nanotube can cause on-resonance and off-resonance behaviors of the spin-coherent transport. The impurity suppresses the conductance for the on-resonance case, while it enhances the conductance for the off-resonance one. With increasing impurity strength, the tunnel magnetoresistance exhibits a maximum or minimum value for the on-resonance or off-resonance case, respectively.     

Electron transport in armchair single-wall carbon nanotubes

The rates of electron scattering via phonons in the armchair single-wall carbon nanotubes were calculated by using the improved scattering theory within the tight-binding approximation. Therefore, the problem connected with the discrepancy of the scattering rates calculated in the framework of the classical scattering theory and ones predicted by experimental data was clarified. Then these results were used for the solving of the kinetic Boltzmann equation to describe electron transport properties of the nanotubes. The equation was solved numerically by using both the finite difference approach and the Monte Carlo simulation procedure.     

Zero-bias anomaly and kondo-assisted quasiballistic 2D transport

Nonequilibrium transport measurements in mesoscopic quasiballistic 2D electron systems show an enhancement in the differential conductance around the Fermi energy. At very low temperatures, such a zero-bias anomaly splits, leading to a suppression of linear transport at low energies. We also observed a scaling of the nonequilibrium characteristics at low energies which resembles electron scattering by two-state systems, addressed in the framework of two-channel Kondo model. Detailed sample-to-sample reproducibility indicates an intrinsic phenomenon in unconfined 2D systems in the low electron-density regime.     

Rapid transport of gases in carbon nanotubes

We report atomistic simulations for both self- and transport diffusivities of light gases in carbon nanotubes and in two zeolites with comparable pore sizes. We find that transport rates in nanotubes are orders of magnitude faster than in the zeolites we have studied or in any microporous material for which experimental data are available. The exceptionally high transport rates in nanotubes are shown to be a result of the inherent smoothness of the nanotubes. We predict that carbon nanotube membranes will have fluxes that are orders of magnitude greater than crystalline zeolite membranes.     

Proton transport through water-filled carbon nanotubes

Proton transfer along 1D chains of water molecules inside carbon nanotubes is studied by simulations. Ab initio molecular dynamics and an empirical valence bond model yield similar structures and time scales. The proton mobility along 1D water chains exceeds that in bulk water by a factor of 40, but is reduced if orientational defects are present. Excess protons interact with hydrogen-bonding defects through long-range electrostatics, resulting in coupled motion of protons and defects.     

Ballistic phonon thermal transport in multiwalled carbon nanotubes

We report electrical transport experiments, using the phenomenon of electrical breakdown to perform thermometry, that probe the thermal properties of individual multiwalled carbon nanotubes. Our results show that nanotubes can readily conduct heat by ballistic phonon propagation. We determine the thermal conductance quantum, the ultimate limit to thermal conductance for a single phonon channel, and find good agreement with theoretical calculations. Moreover, our results suggest a breakdown mechanism of thermally activated C-C bond breaking coupled with the electrical stress of carrying approximately 10(12) A/m2. We also demonstrate a current-driven self-heating technique to improve the conductance of nanotube devices dramatically.     

Electron transport and hot phonons in carbon nanotubes

We demonstrate the key role of phonon occupation in limiting the high-field ballistic transport in metallic carbon nanotubes. In particular, we provide a simple analytic formula for the electron transport scattering length, which we validate by accurate first principles calculations on (6, 6) and (11, 11) nanotubes. The comparison of our results with the scattering lengths fitted from experimental I-V curves indicates the presence of a nonequilibrium optical phonon heating induced by electron transport. We predict an effective temperature for optical phonons of thousands Kelvin.     

Electronic structure and quantum transport in carbon nanotubes

Received: 3 April 1998