单根碳纳米管阴极场致发射特性研究

碳纳米管具有优异的场致发射性能,是一种很有前景的电子发射源。本文初步探讨了纳米材料发射理论机制,利用电磁计算软件CST建立仿真分析模型,并针对其具体结构特点构造了合适的仿真环境,通过仿真计算取得的成果对于研制采用碳纳米管阵列作为场致发射阴极的微波管有重要的理论指导作用。     

双壁碳纳米管的电子显微学研究

本文分析研究了甲酸镍二水合物作为催化剂前驱体,多壁管为原料,采用氢电弧放电法制得的双壁碳纳米管样品中不同管壁数目碳纳米管的分布及双壁碳管直径分布,发现样品中单壁和双壁碳管占主要地位,双壁管的内径主要分布在1.67 nm～3.67 nm之间,外径主要分布在2.33 nm～4.33 nm之间.此外,精确测定了三个双壁碳纳米管的螺旋指数,分别为[(28,3)(29,17)],[(19,8)(29,6)]及[(23,15)(28,22)],其电学性能分别为[半导体性,金属性],[半导体性,半导体性]及[半导体性,金属性].同时,观察了在不同条件下的电子辐照效应.结果表明,经辐照碳管的最内层管壁先发生断裂,其形变速度逐渐变慢,单根碳管易依附于大块物质.在相同的辐照条件下,管壁数目越多碳管越稳定.当管壁数目相同时,直径小的管比直径大的管稳定.高加速电压能够加速碳管的变形.     

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.     

Electronic transport properties of an (8,0) carbon/silicon-carbide nanotube heterojunction

A two-probe system of the heterojunction formed by an (8,0) carbon nanotube(CNT) and an (8,0)silicon carbide nanotube (SiCNT) was established based on its optimized structure. By using a method combining nonequilibrium Green's function (NEGF) with density functional theory (DFT), the transport properties of the heterojunction were investigated. Our study reveals that the highest occupied molecular orbital (HOMO) has a higher electron density on the CNT section and the lowest unoccupied molecular orbital (LUMO) mainly concentrates on the interface and the SiCNT section. The positive and negative threshold voltages are1.8 and-2.2 V, respectively.     

Electrical properties of transparent conducting carbon nanotube films

Single walled-carbon nanotube (SWCNT) thin film is one of the candidates for the next-generation flexible and transparent conductive thin film, which is a crucial component in various applications such as electro-des of flat-panel displays, solar cells, light emitting diodes,and touch panels. An intensive research work is underway to develop thin and flexible SWCNT films. The most important requirement of an SWCNT thin film is that it should show a low sheet resistance coupled with a high transparency. In this work, thin films of SWCNTs are PrePared by vacuum filtration. The electrical properties of the as-prepared, annealed and HNO3-treated SWCNT films have been investigated. It is found that the square resistance can be significantly changed upon anneal and HNO3-treatment. A room-temperature ethanol alcohol sensor based on the SWCNT film has also been demonstrated.     

碳纳米管冷阴极Pierce电子枪

为发展场致发射冷阴极毫米波电真空辐射源器件, 对利用大面积碳纳米管冷阴极产生大电流、高电流密度电子注的电子光学系统进行了研究.通过在Pierce电子枪阴极表面引入栅网结构, 解决了碳纳米管冷阴极场致发射所需的强电场和电子聚束问题.在碳纳米管冷阴极实验测试数据的基础上, 采用粒子模拟软件对上述电子光学系统进行了仿真.研究了栅网对注电流、注腰半径和电子注散射的影响, 分析了阳极电压和外加轴向磁场对电子注的聚束作用.优化后的仿真结果表明在阴极发射面为3.03 cm2时, 该电子光学系统能够产生210 mA、60 kV, 电流密度为6.7 A/cm2, 最大注半径为1mm的电子注.     

Three-dimensional evaluation of an independent multi-walled carbon nanotube probe by tomography with high-resolution transmission electron microscope

We evaluated an independent multi-walled carbon nanotube (MWNT) probe by using tomography with a high-resolution transmission electron microscope to verify the three-dimensional structure of the probe tip. The new method of probe evaluation revealed the following features: (i) cutting the end of the MWNT probe caused the wall structure to disintegrate and encapsulated the graphene sheets fragmented by the discharged pulse; (ii) the cap of the MWNT probe was an open cylinder covered by walls similar in shape to a rectangular slit; (iii) the grooves of the inner walls of the MWNT probe, which were created by the discharge cutting method, maintained a cylindrical shape that was different from the peeling-off mechanism.     

Molecular dynamics study of bamboo-like carbon nanotube nucleation

Molecular dynamics (MD) simulations based on an empirical potential energy surface were used to study the nucleation of bamboo-like carbon nanotubes (BCNTs). The simulations reveal that inner walls of the bamboo structure start to nucleate at the junction between the outer nanotube wall and the catalyst particle. In agreement with experimental results, the simulations show that BCNTs nucleate at higher dissolved carbon concentrations (i.e., feedstock pressures) than those where nonbamboo-like carbon nanotubes are nucleated.     

(8, 0)碳纳米管/碳化硅纳米管异质结输运特性的研究

A two-probe system of the heterojunction formed by an （8, 0） carbon nanotube （CNT） and an （8, 0） silicon carbide nanotube （SiCNT） was established based on its optimized structure. By using a method combining nonequilibrium Green＇s function （NEGF） with density functional theory （DFF）, the transport properties of the het-erojunction were investigated. Our study reveals that the highest occupied molecular orbital （HOMO） has a higher electron density on the CNT section and the lowest unoccupied molecular orbital （LUMO） mainly concentrates on the interface and the SiCNT section. The positive and negative threshold voltages are ＋1.8 and -2.2 V, respectively.     

Optimization of electron beam focusing for gated carbon nanotube field emitter arrays

We fabricated gated field emitter arrays with a novel focusing structure of electron beams, where the focusing electrode concentrically surrounded each gate hole. Carbon nanotube emitters were screen printed inside an amorphous-Si concave well far below the gate. It was theoretically and experimentally verified that the concave well structure effectively focused the emitted electron beams to their designated phosphor pixels by modulating focusing gate voltages. For the vacuum packaged field emission displays with the pixel specification fitting high-definition televisions, color reproducibility of approximately 71% was achieved at the brightness of 400 cd/m/sup 2/.     

碳纳米管卷层结构的TEM研究

碳纳米管发现以来,其结构的研究一直是人们普遍关心的课题。至今为止,已有不少有关碳纳米管结构的报道[1]。给出了一些结构模型,其中以Iijima给出的模型最具有代表性,即认为碳纳米管是由碳原子组成的层面卷成筒状后形成的管状纤维。层面内的碳原子之间以sp2键结合,每个碳原子连接二个碳原子形成一系列连续的六边形(以下简称六圆环)。单层碳纳米管即是由一层卷成筒状的碳原子六圆环组成。而多层碳纳米管则是由多个碳原子六圆环组成的圆筒套在一起组成的。而这些圆筒之间的间距与石墨中碳原子层面间距相等,均为0.34nm。此外还认为碳纳米管的…     

影响碳纳米管阴极场发射性能首要因素的研究

研究了影响碳纳米管(CNT)场发射性能的主要因素,通过实验分析气压、热处理温度、发射体尺寸参数等,发现预先热处理可有效提高发射体分散均匀性,而高温后处理可有效纯化CNT;气压和温度是工作过程中影响CNT阴极膜场发射稳定性的重要参数;而CNT发射体的长度、管径与膜层密度是影响场发射电流特性的主要因素,长径比大小影响着场增强因子大小,大长径比引起低的开启电场强度和高发射电流,但管径的大小与场发射均匀性的优劣呈相反关系.     

碳纳米管悬浮液光限幅机理实验研究

为了研究碳纳米管悬浮液的光限幅机理,测量了碳纳米管悬浮液的散射能量和透射能量随入射激光能量密度的变化曲线,得到了不同入射激光能量密度下,散射光能量在平行于入射线偏振光偏振方向的散射面内的角度分布,并对碳纳米管悬浮液进行了探针光实验。根据米氏散射理论,计算了在不同大小的散射中心下,碳纳米管悬浮液的散射光能量在平行于入射线偏振光偏振方向的散射面内的角度分布,以及散射截面随散射中心半径大小的变化。结果表明,碳纳米管悬浮液光限幅可能源于碳纳米管吸收激光能量汽化形成的碳气泡引起的非线性散射。     

多倍直流偏置电压对碳纳米管薄膜声源的影响

针对碳纳米管薄膜声源系统的输出声信号频率失真问题,提出在交流信号上施加多倍直流偏置电压的方法.从热致发声原理入手,利用碳纳米管薄膜声压理论,分析出增加多倍直流偏置电压后,输出信号中的一倍频与二倍频声压幅值,并探究两者幅值比变化规律.实验结果表明,随着输入频率和直流偏置电压增加,输出声信号中两者幅值之比亦增加,当直流偏置电压是交流电压的两倍后,输出声信号波形与输入电信号近似一致,较好地解决了频率失真问题;同时,输出声压级也有较大幅度提升.     

不同转移法对碳纳米管场发射特性的影响

通过印刷法、喷涂法和电泳沉积法转移经过处理的碳纳米管(CNT)原料到ITO电极上,高温烧结制备CNT阴极阵列,并对CNT的表面形貌和场发射性能进行测试分析。结果表明,不同转移方法对CNT阴极场发射性能的影响不同,印刷法、喷涂法及电泳沉积法3种方法制备CNT阴极场发射的开启电场分别为2.21、1.62和1.85 V/μm;当电场为2.3 V/μm时,喷涂法制备的CNT阴极场发射性能最佳,电泳沉积法制备CNT阴极次之,印刷法制备的CNT阴极最差,并根据金属半导体理论分析其原因。     

Simulation of carbon nanotube FETs with linear doping profile near the source and drain contacts

We propose carbon nanotube field effect transistors (CNTFETs) in which the source and drain regions of the channel (carbon nanotube) have been doped nonuniformly. The MOSFET like CNTFETs (MOSCNTs) suffer from band to band tunneling which in turn causes the ambipolar conduction. In this paper, we propose a linear doping profile for the carbon nanotube (CNT) near the source and drain contacts. This reduces the gradient of each potential barrier at the interface between the intrinsic and doped parts of the CNT and suppresses the band to band tunneling and ambipolar conduction. The device has been simulated by solving coupled Poisson and Schrödinger equations. Non-equilibrium Green’s function (NEGF) method has been used to investigate the transport properties. The uncoupled mode space approach has been used to reduce the computational burden. The calculated energy band diagrams justified improved ambipolar behavior and lower off current.     

Magnetoelectric properties of an electron beam

An electron beam is described as a magnetoelectric medium. Expressions for the energy and power flux densities are deduced and applied to the plane waves propagating in the direction of the beam.     

Intelligent system and electron components for controlling individual heat consumption

An intelligent system and its electron components are developed that implement an innovative method for measuring individual heat consumption. For the intelligent system and its electron components, original design-technological, circuit, hardware, and software solutions are proposed. The methods and mathematical models for evaluating individual heat consumption are developed and validated.     

碳纳米管应用研究

随着对碳纳米管研究的不断深入,对碳纳米管的应用研究越来越受到人们的重视。通过分析碳纳米管的物理特性,对碳纳米管的应用前景进行了广泛的探索。着重分析了碳纳米管的电学特性,如导电特性、通流能力、电流特性及其场发射特性。在此基础上,讨论了碳纳米管在纳米电子学和电子场致发射等方面的应用。同时分析了碳纳米管的磁学特性、力学特性及敏感特性等并讨论了其在纳米机械系统、电磁吸收、传感器及其他领域中的应用。研究表明,碳纳米管在众多的领域具有广泛的应用前景。     

A numerical study of scaling issues for Schottky-barrier carbon nanotube transistors

We performed a comprehensive scaling study of Schottky-barrier (SB) carbon nanotube transistors using self-consistent, atomistic scale simulations. We restrict our attention to SB carbon nanotube field-effect transistors (FETs) whose metal source-drain is attached to an intrinsic carbon nanotube channel. Ambipolar conduction is found to be an important factor that must be carefully considered in device design, especially when the gate oxide is thin. The channel length scaling limit imposed by source-drain tunneling is found to be between 5 nm and 10 nm, depending on the off-current specification. Using a large diameter tube increases the on-current, but it also increases the leakage current. Our study of gate dielectric scaling shows that the charge on the nanotube can play an important role above threshold.