GaAs第一性原理研究

为了深入认识GaAs的电子结构和光学性质,计算和分析了GaAs晶体的能带结构、电子态密度、分渡态密度、光学常数,所有计算都是基于密度泛函理论(DFT)框架下的第一性原理平面渡赝势方法.研究证明,其具有广泛的应用领域.     

第一性原理计算金属原子对石墨烯光电性能的调制

基于第一原理计算,研究最活泼的金属(Na, K,Al)以及实验上常用的金属(Ti, Ag, Ru, Au,Pt)等八种金属原子对石墨烯的功函数和光学性质的调制。结果表明,除了Ti和Ru原子外,所有的吸附原子均失去电子,导致石墨烯的狄拉克锥向低能方向移动。所有吸附结构的功函数均低于本征石墨烯。特别是Ti或Ru原子与石墨烯之间存在较强的相互作用,导致Ti和Ru吸附石墨烯的功函数较小。由于吸附原子的存在,使得石墨烯的光学性质发生了很大的变化。不同吸附结构的静态介电函数差别很大;吸附原子后,石墨烯对可见光和红外光的吸收强度大大增加。     

储氢碳纳米管与氢原子相互作用的量子力学研究

应用ONIOM方法对单壁碳纳米管储氢进行了研究,由高到低分别应用密度泛函(DFT)B3LYP方法、HF方法与AMl方法对其进行了组合计算,优化结果与完全用从头算方法(HF/3-21g*)得到的结果存在着较大出入,分析认为后者的结果较为可靠.使用HF/3-21g*方法对(5,5)5晶胞,(6,6)5晶胞单壁碳纳米管在不同的氢覆盖率下进行结构优化,找出了其相关递变规律性.完全应用B3LYP/3-21g*对一系列的体系进行了单点能的计算,通过势能面扫描数据,得到了单壁碳纳米管储氢的基本模型和储氢过程是化学过程的结论.     

氧化钌/碳纳米管/石墨烯复合电极材料的制备和电化学性能

用水热反应法分别合成了氧化钌(Ru O_2)、多壁碳纳米管(MWCNT)、还原氧化石墨烯(r GO)的二元及三元复合材料,再以此类复合材料制作了电极。采用循环伏安、交流阻抗、恒电流充放电等方法研究了其电化学性能,用扫描电子显微镜(SEM)对其形貌进行了表征。结果表明:三元复合材料能明显提高电极的比容量(562 F/g)和导电性,高于二元复合材料比容量。其中采用层层组装工艺制备的复合电极,比容量达到906 F/g,内阻0.298?。     

钪型阴极表面微观发射结构的模拟计算

在阴极研究领域,钪型阴极因其大发射电流密度受到广泛关注,但其发射机制仍不明确。普遍认为表面发射层为BaxScyOz-W结构,但发射表面是动态变化的,很难确认其最佳表面发射结构。本文对钪型阴极表面BaxScyOz-W的理想发射结构进行了建模,并利用密度泛函方法对其功函数进行了计算。计算得到Ba-O-Sc-O-W表面结构的最小功函数为1.186eV。通过对计算结果的分析,讨论了不同表面原子结构对应的功函数变化。     

激光制备新型石墨烯/铜基复合电触头

为了解决电力系统中关键材料电触头同时受到电弧烧蚀、动静触头相互碰撞产生的冲击载荷和摩擦以及电流产生焦耳热引起的熔焊的问题,提高电气设备的使用性能,发展新型高性能触头材料,提出了一种石墨烯/紫铜复合触头的新型制备方法。采用等离子体辅助加工手段,在质量分数为0.999的紫铜表面上制备出镍铜合金过渡层,在此过渡层上利用高功率连续激光原位制备石墨烯表面薄膜,全覆盖于紫铜基底表面,作为独立涂层来抵抗触头材料所受的破坏,探索了制备石墨烯复合触头材料过程中的等离子体辅助加工工艺以及激光加工工艺。结果表明,石墨烯/铜基触头材料具有优异的电工特性,电阻与紫铜相近,硬度为紫铜的1.8倍,摩擦系数仅为0.06。本研究可为电工材料提供新的解决思路和新的材料体系。     

石墨烯/Si晶体管的研究进展

石墨烯具有很多优异的力学、电学和结构特性,可用于制备高速、低功耗的半导体电子器件和集成电路芯片。简要介绍了三种石墨烯/Si的制备方法,即剥离法、外延法、剪切和选择转移印刷法,其中外延生长的石墨烯被认为是最终实现碳集成电路的唯一途径。并给出了采用上述方法制备的石墨烯/Si晶体管的电阻、磁阻、载流子迁移和输运特性以及量子霍尔效应(QHE)等电学特性。发现石墨烯/Si晶体管最高频率达155GHz,在室温下具有异常的量子霍尔效应和分数量子霍尔效应。其电荷载流子浓度在电子和空穴之间连续变化,可高达1013 cm-2,迁移率可达2×105 cm2/(V.s)。     

锯齿-扶手椅-锯齿型石墨烯纳米带电子输运特性研究

基于密度泛函理论和非平衡格林函数,研究了中心散射区长度对于锯齿-扶手椅-锯齿型石墨烯纳米带(Z-A-ZGNRs)的电子输运特性的影响.结果表明:中心散射区长度对导电性能有很大的影响.散射区长度较小时,在一定区间内具有明显的负微分电阻现象,长度增加时,这种效应减弱.Z-A-ZGNRs在-2～2 V偏压下存在整流现象,散射...     

弯曲锯齿型单壁碳纳米管的电子学特性研究

采用密度泛函数的B3LYP和非平衡格林函数方法分别对锯齿型单壁(5.0)碳纳米管(SWCNT)及外接Au电极后的电子结构和电子传输特性进行了理论研究。另外用同样的方法,对弯曲的SWCNT和外接Au电极的器件的电子结构、电子传输特性进行了研究。比较发现,两个模型在HOMO状态下的电子分布主要集中在两端,总的传输性能比LUMO状态下要弱。虽然两种模型具有相似的能带结构,但弯曲SWCNT的能隙较未弯曲SWCNT的能隙要小。另外两种模型的传输谱与态密度有着明显的对应性,但弯曲的碳纳米管的传输谱较未弯曲碳纳米管的传输谱峰值大很多,说明弯曲过后SWCNT的电子输运性能要远优于未弯曲SWCNT。     

含缺陷碳纳米管的力学性质研究

本文采用全电子密度泛函理论,研究了带有不同拓扑缺陷的碳纳米管在单轴拉伸下的力学性质。计算结果表明：带有7元环和8元环拓扑缺陷的碳纳米管力学性质很接近。两端施加给定轴向应变,二者的能量曲线几乎都在应变约为6．5％时与完好管的能量曲线相交。这表明在拉伸荷载作用下,触发8环和7环拓扑缺陷的临界应变几乎相同。但对于含有9元环拓扑缺陷的碳纳米管,在所考虑的拉伸范围内其能量远高于相应的完好管。这表明此种缺陷形式很难被拉伸加载方式所触发。     

Graphene Reinforced Carbon Nanotube Networks for Wearable Strain Sensors

Transparent, stretchable films of carbon nanotubes (CNTs) have attracted significant attention for applications in flexible electronics, while the lack of structural strength in CNT networks leads to deformation and failure under high mechanical load. In this work, enhancement of the strength and load transfer capabilities of CNT networks by chemical vapor deposition of graphene in the nanotube voids is proposed. The graphene hybridization significantly strengthens the CNT networks, especially at nanotube joints, and enhances their resistance to buckling and bundling under large cyclic strain up to 20%. The hybridized films show linear and reproducible responses to tensile strains, which have been applied in strain sensors to detect human motions with fast response, high sensitivity, and durability.     

基于碳管/石墨烯/GaAs双异质结自驱动的近红外光电探测器

基于单壁碳纳米管(SWCNT)/单层石墨烯/GaAs双异质结结构构筑了自驱动近红外光电探测器,利用GaAs优异的光电特性和石墨烯的高载流子迁移率特点,该光电探测器在无偏压情况下光电响应率可达393.8mA/W,比探测率达到6.48×1011 Jones,开关比为103。而且,利用半导体性SWCNT对近红外光子的高吸收特性以及SWCNT/石墨烯异质结对SWCNT产生光生载流子进行有效分离,使得该双异质结光电器件的光谱响应可拓展至1 064nm,突破了GaAs自身的响应极限860nm。     

Electrical Power From Nanotube and Graphene Electrochemical Thermal Energy Harvesters

Nanocarbon‐based thermocells involving aqueous potassium ferro/ferricyanide electrolyte are investigated as an alternative to conventional thermoelectrics for thermal energy harvesting. The dependencies of power output on thermocell parameters, such as cell orientation, electrode size, electrode spacing, electrolyte concentration and temperature, are examined to provide practical design elements and principles. Observation of thermocell discharge behavior provides an understanding of the three primary internal resistances (i.e., activation, ohmic and mass transport overpotentials). The power output from nanocarbon thermocells is found to be mainly limited by the ohmic resistance of the electrolyte and restrictions on mass transport in the porous nanocarbon electrode due to pore tortuosity. Based on these fundamental studies, a comparison of power generation is conducted using various nanocarbon electrodes, including purified single‐walled and multi‐walled carbon nanotubes (P‐SWNTs and P‐MWNTs, respectively), unpurified SWNTs, reduced graphene oxide (RGO) and P‐SWNT/RGO composite. The P‐SWNT thermocell has the highest specific power generation per electrode weight (6.8 W/kg for a temperature difference of 20 °C), which is comparable to that for the P‐MWNT electrode. The RGO thermocell electrode provides a substantially lower specific power generation (3.9 W/kg).     

Electrical Properties of Carbon Nanotube Based Fibers and Their Future Use in Electrical Wiring

The production of continuous fibers made purely of carbon nanotubes has paved the way for new macro‐scale applications which utilize the superior properties of individual carbon nanotubes. These wire‐like macroscopic assemblies of carbon nanotubes were recognized to have a potential to be used in electrical wiring. Carbon nanotube wiring may be extremely light and mechanically stronger and more efficient in transferring high frequency signals than any conventional conducting material, being cost‐effective simultaneously. However, transfer of the unique properties of individual CNTs to the macro‐scale proves to be quite challenging. This Feature Article gives an overview of the potential of using carbon nanotube fibers as next generation wiring, state of the art developments in this field, and goals to be achieved before carbon nanotubes may be transformed into competitive products.     

Graphene and Carbon Nanotube Auxetic Rubber Bionic Composites with Negative Variation of the Electrical Resistance and Comparison with Their Nonbionic Counterparts

Microorganism metabolic activity can facilitate the formation of cellular material systems that have unusual mechanical and physical properties. In the living world microorganisms are commonly used for preparing porous food by fermentation; here carbon nanotubes, graphene nanoplatelets, and a mix of them are dispersed in liquid silicone rubber with single‐cell fungi of commercial beer yeast. The fermentation of such microorganisms during the gelling of the silicone matrix results in bionic composites with buckled/collapsed cells that infer, as rationalized with an analytical model and excluded in a abiotic experimental comparison, auxetic properties. During stretching it is found that the Poisson's ratio of such composites changes sign, from negative to positive, and the variation of the electrical resistance is negative. In addition to the conductivity increment, a general increment of the stretchability and damage resistance with respect to the composites prepared by abiotic process is observed. Bionic composites, even if in their infancy, can thus be multifunctional and superior to their traditional/abiotic counterparts.     

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.     

准一维碳纳米管的含时输运性质的研究(英文)

提出了一种数值模拟方法,用于研究准一维碳纳米管系统的含时输运特性。基于非平衡格林函数,通过提出的方法,对准一维碳纳米管系统的电学性质进行数值计算。计算结果显示:当同一连续方波作用于电极时,电极与碳纳米管之间的耦合能越大,电流的最初上升值越大,弛豫时间越短;当输入电压为低频正弦信号,响应电流曲线变得不规则。本仿真结果有利于对纳米材料电学性质的评估,为纳米电子器件的设计和优化提供理论指导。     

锯齿型单壁碳纳米管的光电性质

应用基于广义梯度近似的密度泛函理论中的简化广义梯度近似方法(PBE)对(7,0)至(18,0)锯齿型单壁碳纳米管在极化与非极化条件下从紫外波段到近红外波段的光电性质分别做了理论计算,得到了锯齿型碳纳米管的各光学常数峰值和各光学常数峰值所对应的波长与其手性参数n之间的对应关系和变化趋势。结果表明:除反射率和损耗外的各光学常数的峰值是随着n的增大而减小的;除反射率峰值对应波长外,其它光学常数的峰值对应的波长值随着n的增大逐渐趋于一个恒定值。