我们将机电测量与{ \em ab initio}密度泛函计算相结合，解决了多壁碳纳米管中扭转诱导电导振荡起源的争议。根据我们的观察，振荡周期与纳米管直径的平方成反比，正如相同直径的单壁纳米管所预期的那样。这是支持我们的理论发现，微分扭转有效地使费米能级附近的多壁纳米管的壁，并移动量子线的费米动量。我们排除了与壁之间的配准变化相关的另一种解释，因为它会导致振荡周期的不同直径依赖性。
英文摘要：
We combine electromechanical measurements with {\em ab initio} density functional calculations to settle the controversy about the origin of torsion-induced conductance oscillations in multi-wall carbon nanotubes. According to our observations, the oscillation period is inversely proportional to the squared diameter of the nanotube, as expected for a single-wall nanotube of the same diameter. This is supported by our theoretical finding that differential torsion effectively decouples the walls of a multi-wall nanotube near the Fermi level and moves the Fermi momentum across quantization lines. We exclude the alternative explanation linked to registry changes between the walls, since it would cause a different diameter dependence of the oscillation period.
The electronic transport properties of a metallic carbon nanotube with the five-seven disclination pair characterized by a lattice distortion vector are investigated. The influence of the disclination dipole includes induced curvature and mixing of two sublattices. Both these factors are taken into account via a self-consistent perturbation approach. The conductance and the Fano factor are calculated within the transfer-matrix technique. PACS: 73.63.Fg, 72.80.Rj, 72.10.Fk
Fractional quantum conductance in carbon nanotubes
利用基于原子轨道哈密顿量参数化线性组合的散射技术，计算了多壁碳纳米管的弹道量子电导。我们发现，壁间的相互作用不仅阻止了一些量子电导通道，但也重新分配的电流不均匀地在整个结构的各个管。我们的研究结果提供了一个自然的解释，意想不到的整数和非整数电导值报告的多壁纳米管在参考。[S. Frank，P. Poncharal，Z.L. Wang和W. A. de Heer，Science 280，1744（1998）]
We present a first-principles study of the electronic transport properties of micrometer long semiconducting CNTs randomly covered with carbene functional groups. Whereas prior studies suggested that metallic tubes are hardly affected by such addends, we show here that the conductance of semiconducting tubes with standard diameter is on the contrary severely damaged. The configurational averaged conductance as a function of tube diameter and with a coverage of up to one hundred functional groups is extracted. Our results indicate that the search for a conductance-preserving covalent functional…
The phonon and electron transport in single-walled carbon nanotubes (SWCNT) are investigated using the nonequilibrium Green's function approach. In zigzag SWCNT ($n$, 0) with $mod(n,3)\not=0$, the thermal conductance is mainly attributed to the phonon transport, while the electron only has few percentage contribution. The maximum value of the figure of merit ($ZT$) is about 0.2 in this type of SWCNT. The $ZT$ is considerably larger in narrower SWCNT because of enhanced Seebeck coefficient. $ZT$ is smaller in the armchair SWCNT, where Seebeck coefficient is small due to zero band gap. It is fou…
We investigate thermal energy coupling between carbon nanotubes (CNTs) and SiO2 with non-equilibrium molecular dynamics simulations. The thermal boundary conductance (g) per unit CNT length is found to scale proportionally with the strength of the Van der Waals interaction (~X), with CNT diameter (~D), and as a weak power law of temperature (~T^1/3 between 200-600 K). The thermal relaxation time of a single CNT on SiO2 is independent of diameter, tau ~ 85 ps. With the standard set of parameters g ~ 0.1 W/m/K for a 1.7 nm diameter CNT at room temperature. Our results are comparable to, and expl…
A Theoretical Study on Spin-Dependent Transport of "Ferromagnet/Carbon Nanotube Encapsulating Magnetic Atoms/Ferromagnet" Junctions with 4-Valued Conductances
We use the energy analysis as a perturbative method to study the effect of electron-radial breathing mode (RBM) phonon interaction on the electrical conductivity of long metallic zigzag carbon nanotubes (CNTs). The band structure of zigzag CNTs is calculated by exerting zone-folding method on relations derived by using the nearest neighbor approximation of tight-binding expression for the $π$ valence and conduction bands of graphene. The small hollow cylinder model, with two different approximations, is used to obtain the RBM frequency in our calculation. As the result, we have calculated the …
Random networks of single-walled carbon nanotubes (CNTs) usually contain both metallic (m-CNTs) and semiconducting (s-CNTs) nanotubes with an approximate ratio of 1:2, which leads to a trade-off between on-conductance and on/off ratio. We demonstrate how the design problem can be solved with a realistic numerical approach. We determine CNT density, length, and channel dimensions for which CNT thin-film transistors (TFTs) simultaneously attain on-conductance higher than $1~{\rm μS}$ and on/off ratio higher than $10^4$. Fact that asymmetric systems have more pronounced finite-size scaling behavi…
Motivated by recent experiments on electronic transport through a carbon nanotube, we investigate the role of the intra- and inter-orbital Coulomb interactions on the temperature evolution of the conductance. It is shown that small amount (~10%) of asymmetry between these Coulomb repulsions substantially deforms the conductance profile at finite temperature, particularly around half-filling. The nature of such thermal symmetry crossover is elucidated.
We present an approach for time-dependent quantum transport based on a self-consistent non-equilibrium Green function formalism. The technique is applied to a ballistic carbon nanotube transistor in the presence of a time harmonic signal at the gate. In the ON state the dynamic conductance exhibits plasmonic resonant peaks at terahertz frequencies. These vanish in the OFF state, and the dynamic conductance displays smooth oscillations, a signature of single particle quantum effects. We show that the nanotube kinetic inductance plays an essential role in the high-frequency behavior.
By developing a two-dimensional (2D) full quantum simulation, the attributes of carbon nanotube field-effect transistors (CNTFETs) in different temperatures have been comprehensively investigated. Simulations have been performed by employing the self-consistent solution of 2D Poisson-Schrodinger equations within the nonequilibrium Green's function (NEGF) formalism. Principal characteristics of CNTFETs such as current capability, drain conductance, transconductance, and subthreshold swing (SS) have been investigated. Simulation results present that the drain conductance and on-current of the CN…
In ferromagnetic nanostructures, the ballistic anisotropic magnetoresistance (BAMR) is a change in the ballistic conductance with the direction of magnetization due to spin-orbit interaction. Very recently, a directional dependent ballistic conductance has been predicted to occur in a number of newly synthesized nonmagnetic semiconducting nanostructures subject to externally applied magnetic fields, without necessitating spin-orbit coupling. In this article, we review past works on the prediction of this BAMR effect in core-shell nanowires and rolled-up nanotubes. This is complemented by new r…
Well-known conductive molecular wires, like cumulene or polyyne, provide a model for interconnecting molecular electronics circuit. In the recent experiment, the appearance of carbon wire bridging two-dimensional electrodes - graphene sheets - was observed [PRL 102, 205501 (2009)], thus demonstrating a mechanical way of producing the cumulene. In this work, we study the structure and conductance properties of the carbon wire suspended between carbon nanotubes (CNTs) of different chiralities (zigzag and armchair), and corresponding conductance variation upon stretching. We find the geometrical …
Recent molecular dynamic simulations have found chiral single wall carbon nanotubes (SWNTs) twist during stretching, which is similar to the motion of a screw. Obviously this phenomenon, as a type of curvature-chirality effect, can not be explained by usual isotropic elastic theory of SWNT. More interestingly, with larger axial strains (before buckling), the axial strain induced torsion (a-SIT) shows asymmetric behaviors for axial tensile and compressing strains, which suggests anharmonic elasticity of SWNTs plays an important role in real a-SIT responses. In order to study the a-SIT of chiral…
