Cavity Quantum Electrodynamics,Nanophotonics, and Quantum Communication with Atomically Doped Carbon Nanotubes

The latest theoretical studies of the near-field electrodynamic properties of atomically doped carbon nanotubes are reviewed. It has been shown that, similar to semiconductor microcavities and photonic band-gap materials, carbon nanotubes may qualitatively change the character of the atom–electromagnetic-field interactions, yielding strong atom–field coupling and the formation of quasi-one-dimensional atomic polariton states. A scheme for entangling such polaritons has been considered, and small-diameter metallic nanotubes have been shown to result in sizable amounts of the two-quantum bit (qubit) atomic entanglement with no damping for sufficiently long times. This challenges novel applications of atomically doped carbon nanotubes in quantum information science.     

Modifying the Electronic Character of Single‐Walled Carbon Nanotubes Through Anisotropic Polymer Interaction: A Raman Study

Using Raman spectroscopy, we demonstrate that the anisotropic interaction between single‐walled carbon nanotubes (SWNTs) and poly(methyl methacrylate) (PMMA) causes significant changes in the electronic properties of their composites. Two different procedures were used to prepare the composites: melt blending and in‐situ UV polymerization. Resonant Raman studies relate the electronic density of states (DOS) of the SWNTs to the corresponding vibration symmetry changes of both the PMMA and the SWNTs. Our results show that, in the melt‐blended sample, the SWNTs—originally semiconducting—became predominantly metallic. The changes in the electronic properties were also confirmed by dielectric constant measurements. We propose that the anisotropic interaction between PMMA and SWNTs in the melt‐blended composite is the dominant reason for the observed electronic character change.     

碳纳米管/石墨烯复合结构的第一性原理计算

为了研究碳纳米管/石墨烯复合结构的电学性质,采用密度泛函理论(DFT)下的第一性原理,对四种T型复合结构进行了几何结构优化,分析了该复合结构的结合能,能带结构,电子态密度,Mulliken电荷分布及功函数.结果表明复合结构均表现出半导体性质,其稳定性及电子结构取决于碳纳米管类型和复合结构的连接方式,而且复合材料的功函数...     

Fundamental transmitting properties of carbon nanotube antennas

Fundamental properties of dipole transmitting antennas formed by carbon nanotubes are investigated. Since carbon nanotubes can be grown to centimeter lengths, and since they can be metallic, the properties of carbon nanotubes as antenna elements are of fundamental interest. In this paper, dipole carbon nanotube antennas are investigated via a classical Hallen's-type integral equation, based on a quantum mechanical conductivity. The input impedance, current profile, and efficiency are presented, and the radiation pattern is discussed, as are possible applications.     

Highly Conductive Redox Protein–Carbon Nanotube Complex for Biosensing Applications

The integration of redox proteins with nanomaterials has attracted much interest in the past years, and metallic single‐walled carbon nanotubes (SWNTs) have been introduced as efficient electrical wires to connect biomolecules to metal electrodes in advanced nano‐biodevices. Besides preserving biofunctionality, the protein–nanotube connection should ensure appropriate molecular orientation, flexibility, and efficient, reproducible electrical conduction. In this respect, yeast cytochrome c redox proteins are connected to gold electrodes through lying‐down functionalized metallic SWNTs. Immobilization of cytochromes to nanotubes is obtained via covalent bonding between the exposed protein thiols and maleimide‐terminated functional chains attached to the carbon nanotubes. A single‐molecule study performed by combining scanning probe nanoscopies ascertains that the protein topological properties are preserved upon binding and provides unprecedented current images of single proteins bound to carbon nanotubes that allow a detailed I–V characterization. Collectively, the results point out that the use as linkers of suitably functionalized metallic SWNTs results in an electrical communication between redox proteins and gold electrodes more efficient and reproducible than for proteins directly connected with metal surfaces.     

A diameter-selective chiral separation of single-wall carbon nanotubes using nitronium lons

We propose a method for a diameter-selective removal of metallic single-walled carbon nanotubes (m-SWCNTs) from semiconducting (s-) ones. Our separation technique is capable of 100% separation of semiconducting and metallic nanotubes for small diameter nanotubes. We dispersed SWCNT powder by sonication in a mixed solution of tetramethylene sulfone and chloroform, where nitronium ions were well disolved. Positively charged nitronium ions were intercalated into nanotube bundles, where the intercalation was promoted also by the counter ions. Nitronium ions selectively attacked the sidewall of m-SWCNTs due to the abundant presence of electron density at the Fermi level, thus yielding stronger binding energy compared to the counterpart s-SWCNTs. The s-SWCNTs were left on the filter after filtration, whereas m-SWCNTs were perfectly destroyed by nitronium ions and drained away as amorphous carbons. This preferable adsorption became obscured for nanotubes with diameters greater than 1.1 nm. The effectiveness of removing m-SWCNTs was confirmed by the transmission electron microscope observations, x-ray photoemission spectra, resonant Raman spectra, and absorption spectra.     

氢吸附开口碳纳米管场发射密度泛函研究(英文)

利用第一性原理密度泛函的方法对氢分子吸附开口碳纳米管的场发射性质进行了综合研究,建立了(5,5)开口碳纳米管吸附不同氢分子数量的吸附模型,并对加电场和未加电场下的模型进行了吸附能、最高占有分子轨道-最低未占分子轨道(HOMO-LUMO)帯隙及诱导偶极矩的计算和分析。计算结果表明吸附能随着电场的增加而变大,吸附稳定性增强。吸附氢分子的碳纳米管在施加外电场后,HOMO-LUMO帯隙明显减小,费米能级附近的局域态密度随着氢分子的吸附而增加。氢分子对碳纳米管的吸附可以在其尖端表面产生诱导偶极矩,导致电荷由碳纳米管向氢分子大量转移,从而驱使电子由碳纳米管尖端发射到真空中,提高了碳纳米管的场发射性能。     

High energy-resolution electron energy-loss spectroscopy study of the electric structure of double-walled carbon nanotubes

Electron energy-loss spectra were obtained from two double-walled carbon nanotubes (DWCNTs) with an energy resolution of 85 meV. The spectra showed multiple peak structures between 2 and 3 eV. However, peak positions are different for these two DWCNTs. The chiral indices of CNT layers of the two DWCNTs were determined to be (29,4)(in) (17,8)(out) and (46,6)(out) (26,21)(in), respectively, by comparing experimental electron diffraction patterns with simulated ones. The spectra were also compared with simulated joint density of states, which were derived from the determined chiral indices. It was confirmed that the peak structures in the spectra are due to interband transitions intrinsic for tubular structures of graphitic sheets.     

Transport effects on signal propagation in quantum wires

Currently, nanowire-based circuits are being considered as candidates for future high-speed electronics. Signal propagation in metallic carbon nanotubes has been analyzed using the Luttinger liquid theory to develop a transmission-line model showing features that can not be obtained from conventional transmission-line theory. The Luttinger liquid theory, however, is governed by strict conditions which restrict its application to metallic carbon nanotubes and it can not be used for any nanowire in general. In this paper, we present a unified theory that can be applied to wires ranging all the way from conventional three-dimensional conductors to one-dimensional carbon nanotubes. We show that when the number of current-carrying modes is less than a critical value, and the small-signal propagation characteristics are significantly influenced by transport effects which go beyond the conventional transmission-line theory. We also use our model to quantitatively examine a few potential applications.     

激光诱导碳纳米管制备石墨烯纳米带及其电学性能分析

通过将纳米管解压缩可以很容易地生产石墨烯纳米带,因为碳纳米管结构可以被认为是卷起的石墨烯筒。这是一种特殊的2D石墨结构,具有出色的性能。应用领域广泛,包括晶体管、光学和微波通信设备、生物传感器、化学传感器、电子存储和处理设备以及纳米机电系统和复合材料。通过扫描电子显微镜（SEM）观察薄膜的形貌,通过拉曼光谱法表征石墨烯的性质,并通过半导体参数测量系统测量薄膜的电导率。拉曼光谱表明,通过优化工艺可以增强石墨烯的拉曼特性。碳纳米管制备石墨烯带的两个重要参数是激光能量密度和辐照时间。在这项研究中,通过准分子激光辐照碳纳米管薄膜来生产石墨烯纳米带。实验结果表明,在150 mJ的激光能量下,观察到连接时碳纳米管没有打开。在450 mJ的能量下,可以有效地破坏碳纳米管,并且使其部分地形成石墨烯带。此时,膜的电导率达到最大值。由于蓄热作用,在碳纳米管壁上出现大量的多孔结构。     

An Integral Formulation for the Electrodynamics of Metallic Carbon Nanotubes Based on a Fluid Model

An integral formulation to model, in the frequency domain, the electromagnetic response of three-dimensional (3-D) structures formed by metallic carbon nanotubes and conductors, within the framework of the classical electrodynamics, is described. The conduction electrons of the metallic nanotube are modeled as an infinitesimally thin cylindrical layer of compressible fluid, whose dynamics are described by means of the linearized hydrodynamic equations. The resulting integral equations are solved numerically by the finite element method using the facet elements and the null-pinv decomposition. The proposed formulation is applied to study carbon nanotube interconnects and dipole antennas and some related results are outlined. The solutions highlight the high-frequency effects due to the electron inertia and the fluid pressure. In particular, since the kinetic inductance matrix dominates over the magnetic one, proximity effects are negligible.     

电化学双电层电容器的研制

通过催化裂解法制备了碳纳米管并进一步制备了碳纳米管薄膜电极。基于该种材料的超电容器电极比容量达到36 F/g并表现出良好的功率特性。本文采用多种研究方法对基于该种材料的双电层电容器进行了详细的研究。     

Replacing Copper Wires with Carbon Nanotube Wires in Electrical Transformers

Carbon nanotubes, with their unique physical properties, have the potential to outperform conventionally used electrical wiring metals. Any improvement in this area of technology would be of great importance to industry, the economy, and the environment, as the global need for electrical energy and its efficient transfer and conversion rapidly increases. Carbon nanotube fibers, which are assemblies made purely of carbon nanotubes, can uniquely be used in macroscopic electrical applications including electrical wires and devices where the operation is enabled by these conductors. This paper presents details of the working prototype of an electrical machine, a transformer, where conventional copper wires have been replaced with conducting wires made purely of carbon nanotube fibers.     

Mixed carbon nanotube bundles for interconnect applications

The increasing resistivity of copper with scaling and demands for higher current density are the driving forces behind the ongoing investigation for new wiring solutions for deep nanometer scale VLSI technologies. Metallic carbon nanotubes (CNTs) are promising candidates that can potentially address the challenges faced by copper, and thereby extend the lifetime of electrical interconnects. This article examines the state of the art in CNT applications with focus on CNT interconnect research. It is observed that individually, single-wall carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs) exhibit characteristics that can be better exploited when a combination of the two is used – in the form of a CNT bundle that plays a vital role in interconnect applications. The focus here is that the usage of a combination of SWCNT (at the centre area of the bundle) and MWCNT (on the outside) provides great performance boost with lower interaction and crosstalk between neighbouring CNT bundles. Simulation results show that the resistance, capacitance, and inductance of a CNT depend on the probability of metallic CNTs present in the bundle and the length of the nanotube. Because Cu is metallic, it indicates that using a higher number of metallic nanotubes in the bundle would aid the CNT bundle performance. In addition, using MWCNT on the outer periphery of the bundle and SWCNT in the centre of the bundle would be the ideal way to maximise the performance of the bundle. Based on the observations we provide an analysis of why a mixed CNT bundle would be highly suitable as interconnections.     

Characterization and estimation of tunnel barrier height in metallic single-wall carbon nanotube quantum dots

A tunnel barrier height has been estimated in quantum dots (QDs) formed in metallic single-wall carbon nanotubes (SWNTs), where QDs can be fabricated simply by depositing metallic contacts on top of the nanotube. Transport measurements have been carried out in a temperature range between 1.5 and 300 K, and revealed single and multi-QD behaviors in different samples at low temperatures. The Arrhenius plot gave an activation energy of ∼6 meV for the barrier formed very likely at the metal-SWNT interface for the single QDs, and two activation energies for seemingly double dots. The latter case comes from the unintentional tunnel barrier due to defects. Discussions on the QD formation and suggestions for a higher temperature operation are given.     

N-CNTs-Based Composite Membrane Engineered By A Partially Embedded Strategy: A Facile Route To High-Performing Zinc-Based Flow Batteries

Zinc-based flow batteries are promising for distributed energy storage due to their low-cost and high-energy density advantages. One of the most critical issues for their practical application is the reliability that results from the heterogeneous zinc deposition and dead zinc from falling off the electrode. Herein, nitrogen-doped carbon nanotubes (N-CNTs)-based composite membrane through a facilely partially embedded method is reported to enable a dendrite-free alkaline zinc-based flow battery. The results indicate that the electrically conductive N-CNTs functional layer can enhance the transport dynamics of charge carriers and homogenize electric field distribution in membrane–electrode interface, which induces the initial nucleation of metallic zinc from the carbon felt electrode to N-CNTs functional layer and further achieve a uniform and dense plating of metallic zinc in alkaline media. Thus, the engineered membrane enables a stable alkaline zinc–iron flow battery performance for more than 350 h at a current density of 80 mA cm⁻². Moreover, an energy efficiency of over 80% can be afforded at a current density of 200 mA cm⁻². The scientific finding of this study provides a new strategy on composite membranes design and their capability to adjust the plating of metallic zinc in alkaline media.     

硅纳米管结构和电子性质的第一性原理研究

基于密度泛函理论的第一性原理方法,在广义梯度近似下,研究了(5,0)和(5,5)硅纳米管结构和电子性质。计算结果表明:(5,0)管硅原子相邻键长波动范围为0.068 nm,大于(5,5)管的0.006 nm;通过对(5,0)管的分波态密度进行分析发现,其3s电子和2p电子能量分布在-13～3 eV,但2p电子集中分布在能量较高的-6～3 eV,出现了明显的sp3轨道杂化。同时对(5,0)和(5,5)硅纳米管最高占据轨道和最低未占据轨道的能隙进行了分析,发现两种管导电性能与结构的手性相关,锯齿型(5,0)管能带交叠具有明显的金属性,而扶手型(5,5)管能隙为0.151 eV是半导体纳米管。     

The Critical Role of the Underlayer Material and Thickness in Growing Vertically Aligned Carbon Nanotubes and Nanofibers on Metallic Substrates by Chemical Vapor Deposition

Vertically aligned carbon nanotubes and nanofibers are grown on metallic Ta and Pd underlayers at temperatures below 500 °C. Controlling the size of the grains of the underlayer film is critical because this leads to a more uniform distribution of catalyst dots, which in turn results in vertical alignment of the carbon nanostructures. Rapid and limited heating and appropriate materials selection can also be used to limit catalyst/underlayer reactions that hinder or suppress carbon nanostructure growth or that lead to entangled growth. Control of catalyst reactivity with metallic underlayers is significant because growth on conductive substrates is notoriously difficult, but needed for many applications such as the use of carbon nanostructures in microelectronic circuits.     

半导体单壁碳纳米管光电特性研究新进展

介绍了半导体和金属型两类单壁碳纳米管的快速分类法,概述了它们的发光机理及其最新应用,所做的数值计算与已有的实验结果相一致。     

零维量子阱的电子结构

<正> 最近半导体超晶格已经由二维发展到一维,甚至零维。因为在零维超晶格中电子运动在三个方向上受到约束,预料将会出现更加明显的量子尺寸效应,例如:将出现一系列分立的量子能级,这些能级与超晶格的大小有很强的依赖关系。目前,已经有一些零维超晶格光学和电学性质的测量。在微电子领域,已经有人将硅的超细微粒排成有规则的列阵,试图构造记忆元件。在化学领域,半导体的微细晶粒可用作催化剂或光敏器等。