Field-modulated carrier transport in carbon nanotube transistors

We have investigated the electrical transport properties of carbon nanotube field-effect transistors as a function of channel length, gate dielectric film thickness, and dielectric material. Our experiments show that the bulk properties of the semiconducting carbon nanotubes do not limit the current flow through the metal/nanotube/metal system. Instead, our results can be understood in the framework of gate and source-drain field induced modulation of the nanotube band structure at the source contact. The existence of one-dimensional Schottky barriers at the metal/nanotube interface determines the device performance and results in an unexpected scaling behavior.     

First-principles study of current–voltage characteristics of two-terminal carbon nanostructures

We present the first-principles investigation of the transport properties of nanotubes connected to metal electrodes under external bias potential. We have developed the technique to calculate the current–voltage (I–V) curves by using the local-density approximation in the density-functional theory. We apply this technique to Al-nanotube-Al systems with different contact geometries regarding the position, the orientation, and the distance of nanotube to the electrode. These different geometries at contact can play an important role in the transport properties. The I–V curves have the different behaviors although the nanotube is connected to the same electrode. The transmission rate from one electrode to the other electrode shows strong dependence on the contact geometry.     

Electronic transport properties of junctions between carbon nanotubes and graphene nanoribbons

Using the tight-binding model and Green’s function method, we studied the electronic transport of four kinds of nanotube-graphene junctions. The results show the transport properties depend on both types of the carbon nanotube and graphene nanoribbon, metal or semiconducting. Moreover, the defect at the nanotube-graphene interface did not affect the conductance of the whole system at the Fermi level. In the double junction of nanotube/nanoribbon/nanotube, quasibound states are found, which cause antiresonance and result in conductance dips.     

Contact resistance of quantum tubes

We consider the conductance of a quantum tube connected to a metallic contact. The number of angular momentum states that the tube can support depends on the strength of the radial confinement. We calculate the transmission coefficients which yield the conductance via the Landauer formula, and discuss the relation of our results to armchair carbon nanotubes embedded in a metal. For Al and Au contacts and tubes with a realistic radial confinement we find that the transmission can be close to unity corresponding to a contact resistance close to h / 2 e²per band at the Fermi level in the carbon nanotube.     

一种平行栅碳纳米管阵列阴极的场发射特性研究

建立一种平行栅碳纳米管阵列阴极,利用悬浮球模型和镜像电荷法进行计算,给出碳纳米管顶端表面电场与电场增强因子的解析式. 在此基础上,进一步分析器件各类参数以及接触电阻对阴极电子发射性能的影响. 分析表明,碳纳米管间距大约为2倍碳纳米管高度时阵列阴极的分布密度最佳,靠边缘部位的碳纳米管发射电子能力比其中心部位的大;除碳纳米管的长径比之外,栅极宽度和栅极间距也对电场增强因子有一定作用;接触电阻的存在大幅度降低碳纳米管顶端表面电场与发射电流,而接触电阻高于800 kΩ时,器件对阳极驱动电压的要求更高. 关键词： 平行栅碳纳米管阵列 悬浮球 场增强因子 接触电阻     

Multiwalled carbon nanotubes are ballistic conductors at room temperature

Following the experiments of Frank et al. [1], which demonstrated quantum transport in multiwalled carbon nanotubes, there have been several experiments that appear to contradict the main conclusion of that paper, which is that the transport of a MWNT at room temperature is ballistic. Here we demonstrate that the intrinsic resistance of clean-arc-produced carbon nanotubes is at most 200 Ω/ μm, which implies that the momentum mean free path is greater than 30 μm, which in turn is much larger than the tube length. This implies that these tubes are ballistic, according to the standard definition of ballistic transport. We also show that the contact resistance with mercury is quite large: a nanotube in contact with Hg over 100 nm of its length still represents a 3000 Ω resistance. Received: 14 September 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002     

碳纳米管表面金纳米颗粒的形成与结构转变

利用分子动力学模拟研究了室温下金纳米颗粒在碳纳米管表面的结构和作用能.研究结果表明,金纳米颗粒随着尺寸的增大会发生不同于孤立状态下的结构转变.当原子数小于130时,颗粒属于无序结构;当原子数大于140时,呈现面心立方晶体结构.小金纳米颗粒和碳纳米管结合紧密,相互作用能正比于面对碳纳米管的颗粒表面面积. 关键词： 金纳米颗粒 碳纳米管 分子动力学模拟     

Multiscale simulation of carbon nanotube devices

In recent years, the understanding and accurate simulation of carbon nanotube-based devices has become very challenging. Conventional simulation tools of microelectronics are necessary to envision the performance and use of nanotube transistors and circuits, but the models need to be refined to properly describe the full complexity of such novel type of devices at the nanoscale. Indeed, many issues such as contact resistance, low dimensional electrostatics and screening effects, as well as nanotube doping or functionalization, demand for more accurate quantum approaches. In this article, we review our recent progress on multiscale simulations which aim at bridging first principles calculations with compact modelling, including the comparison between semi-classical Monte Carlo and quantum transport approaches. To cite this article: C. Adessi et al., C. R. Physique 10 (2009).     

用散粒噪声测量碳纳米管中Luttinger参数

将碳纳米管的载流子输运用基本电荷为ge的Fermi液态模型描述，利用散射理论计算出纳米管中的零频率散粒噪声，在绝对零度下，存在一个强势垒的碳纳米管的散粒噪声为2geI.提出了一种测试纳米管Luttinger参数的新方法：在纳米管上形成一个强势垒，通过测试其散粒噪声，就可以计算出g因子. 关键词： 碳纳米管 Luttinger参数 散粒噪声 散射理论     

Synthesis, integration, and electrical properties of individual single-walled carbon nanotubes

High-quality single-walled carbon nanotubes (SWNTs) are synthesized by chemical vapor deposition (CVD) of methane on silicon-dioxide substrates at controlled locations using patterned catalytic islands. With the synthesized nanotube chips, microfabrication techniques are used to reliably contact individual SWNTs and obtain low contact resistance. The combined chemical synthesis and microfabrication approaches enable systematic characterization of electron transport properties of a large number of individual SWNTs. Results of electrical properties of representative semiconducting and metallic SWNTs are presented. The lowest two-terminal resistance for individual metallic SWNTs (≈5 μm long) is ≈16.5 kΩ measured at 4.2 K. Received: 17 May 1999 / Accepted: 18 May 1999 / Published online: 14 July 1999     

AC transport in carbon-based devices: challenges and perspectives

Time-dependent fields are a valuable tool to control fundamental quantum phenomena in highly coherent low dimensional electron systems. Carbon nanotubes and graphene are a promising ground for these studies. Here we offer a brief overview of driven electronic transport in carbon-based materials with the main focus on carbon nanotubes. Recent results predicting control of the current and noise in nanotube based Fabry–Pérot devices are highlighted. To cite this article: L.E.F. Foa Torres, G. Cuniberti, C. R. Physique 10 (2009).     

Reliability of fluctuation-induced transport in a Maxwell-demon-type engine

We study the transport properties of an overdamped Brownian particle which is simultaneously in contact with two thermal baths. The first bath is modeled by an additive thermal noise at temperature T _A . The second bath is associated with a multiplicative thermal noise at temperature T _B . The analytical expressions for the particle velocity and diffusion constant are derived for this system, and the reliability or coherence of transport is analyzed by means of their ratio in terms of a dimensionless Péclet number. We find that the transport is not very coherent, though one can get significantly higher currents.     

A fluid-physics approach for determining the strength of the coupling between a multiwalled carbon nanotube and a liquid metal contact

We propose a novel fluid-physics formulation to calculate the strength of the coupling between a multiwalled carbon nanotube and a reservoir represented by a liquid-metal contact. Typically, this liquid metal can be mercury or gallium so that the molecules of these two metals are diatomic in liquid state allowing to treat the molecules in question as Morse oscillators whose quantum energy levels are the starting point for evaluating the tube–metal contact coupling.     

Spin-Filter Effect Induced by Magnetic Edge States of Zigzag Carbon Nanotube

Spin-filter effect is predicted in a weak coupled junction composed of a nonmagnetic metal electrode and a zigzag carbon nanotube. This effect is induced by the magnetic edge states of the nanotube, and can produce spin- polarized current in the absence of an external magnetic field. We find that the spin polarization of the current changes its sign at the half-filling point of the nanotube, thus electric field control of spin transport can be realized. Furthermore, we find the coupling strength of the junction may cause a magnetic transition on the edge of the nanotube.     

多壁碳纳米管/聚丙烯复合材料热导率研究

用Pt细丝代替已有3ω方法中的薄膜热线,并设计了基于Labview程序的虚拟测量系统,准确、方便地测量了聚丙烯复合材料的热导率. 测量结果发现,多壁碳纳米管/丁苯橡胶/聚丙烯三元复合材料的热导率随着多壁碳纳米管/丁苯橡胶粉末含量的增加变化不大;多壁碳纳米管/聚丙烯复合材料的热导率随着多壁碳纳米管含量增加而增大;复合材料热导率远小于简单混合规则预测的结果,而与有效介质理论符合很好. 关键词： ω法')" href="#">3ω法 多壁碳纳米管 聚丙烯复合材料 热导率     

Spin-flip shot noise in a quantum dot coupled to carbon nanotube terminals responded by a rotating magnetic field

We have investigated the spectral density of shot noise of the system with a quantum dot (QD) coupled to two single-wall carbon nanotube terminals, where a rotating magnetic field is applied to the QD. The carbon nanotube (CN) terminals act as quantum wires which open quantum channels for electrons to transport through. The shot noise and differential shot noise exhibit novel behaviors originated from the quantum nature of CNs. The shot noise is sensitively dependent on the rotating magnetic field, and the differential shot noise exhibits asymmetric behavior versus source-drain bias and gate voltage. The Fano factor of the system exhibits the deviation of shot noise from the Schottky formula. The super-Poissonian and sub-Poissonian shot noise can be achieved in different regime of source-drain bias.     

ZA27/CNT界面特性电子理论研究

依据原子结合能定义了界面结合能. 采用递归法计算了纳米管增强锌铝基复合材料中ZA27/CNT界面电子结构，揭示了纳米管在ZA27合金晶界分布的微观物理本质，及其ZA27/CNT弱界面结合的电子层面的原因. 研究发现：金属基体对纳米管增强相上的碳原子态密度影响很大，而纳米管对基体金属中的铝、锌原子影响很小. 碳原子态密度与基体金属原子趋于同化，使纳米管与基体金属结合，但因同化程度不高导致界面结合较弱，影响强化效果. 如果在纳米管装饰或镀上与基体金属性质相近的原子层，会极大改善复合材料的界面结合强度，提高复合材料性能. 关键词： 复合材料 纳米管 电子结构 界面     

Carbon nanotubes adhesion and nanomechanical behavior from peeling force spectroscopy

Applications based on single walled carbon nanotube (SWNT) are good example of the great need to continuously develop metrology methods in the field of nanotechnology. Contact and interface properties are key parameters that determine the efficiency of SWNT functionalized nanomaterials and nanodevices. In this work we have taken advantage of a good control of the SWNT growth processes at an atomic force microscope (AFM) tip apex and the use of a low noise (10⁻¹³ m/√Hz) AFM to investigate the mechanical behavior of a SWNT touching a surface. By simultaneously recording static and dynamic properties of SWNT, we show that the contact corresponds to a peeling geometry, and extract quantities such as adhesion energy per unit length, curvature and bending rigidity of the nanotube. A complete picture of the local shape of the SWNT and its mechanical behavior is provided.     

Contact dependence of carrier injection in carbon nanotubes: an ab initio study

We combine ab initio density functional theory with transport calculations to provide a microscopic basis for distinguishing between good and poor metal contacts to nanotubes. Comparing Ti and Pd as examples of different contact metals, we trace back the observed superiority of Pd to the nature of the metal-nanotube hybridization. Based on large scale Landauer transport calculations, we suggest that the optimum metal-nanotube contact combines a weak hybridization with a large contact length between the metal and the nanotube.     

Contact transparency inducing negative differential resistance in nanotube–molecule–nanotube junction predicted by first-principles study

We construct a molecular junction where propyl contacts two armchair carbon nanotubes through five-member ring and perform the first-principles calculations of its transport properties. The negative differential resistance effect with peak-to-valley ratio of 700% is present. Our investigations indicate that contact transparency can induce negative differential resistance in nanotube–molecule–nanotube junction, which may promise the potential application in nano-electronics devices in the future.