CNT界面水分子动力学特性研究

采用非平衡态分子动力学模拟方法研究了碳纳米管(CNT)入口界面的水分子输运特性,分析了不同CNT直径下,水分子动力学特性的变化规律。结果表明,随着CNT直径的增大,水分子流入CNT的通量逐渐增大;界面处水分子密度沿轴向分布更加均匀且逐渐趋近于体相区域的水分子密度。由于大管径CNT对水分子热运动的约束减弱,水分子间相互扰动增强,使得CNT内部的氢键寿命逐渐缩短,有效降低界面传质能量壁垒并改善了水分子输运特性。本文的研究有助于深化对纳米多孔介质入口界面流体的输运特性理解,并为纳米多孔材料的优化设计提供基础理论指导。     

Decoration of multi-walled carbon nanotubes with noble- and transition-metal clusters and formation of CNT–CNT networks

Carbon nanotubes are of great interest because of their outstanding mechanical, chemical and electric properties. The decoration of multi-walled carbon nanotubes with metal clusters of gold, palladium, iron, cobalt and nickel opens even more applications, especially the growth of complex conductor networks in microelectronic devices. PACS 81.07.De; 81.16.Be; 82.30.Nr; 82.33.Hk     

Electrical transport properties of a CNT/C<Subscript>60</Subscript>/CNT hybrid junction with closed end CNT leads using Green’s function method

We investigate transport properties of an all-carbon molecular device consisting of a CNT/C₆₀/CNT hybrid system with closed end (5,5) CNT leads. Two different ways of coupling are considered for C₆₀ molecule through one and five atoms to the cap-edges of CNTs. Our calculations are based on the Green’s function method in the nearest neighbor tight-binding approximation in the coherent regime. In this paper, the sensitivity of electron transport on the geometry of the CNT electrodes-C₆₀ interface is shown. Within the framework of the Landauer-Buttiker formalism, the electrical transmission and current-voltage characteristic are calculated at room temperature. We have investigated the effect of a gate voltage on the current in the considered geometry. In the considered structure, the appearance of the conductance resonances is a manifestation of resonant states of CNT caps, which lie within the HOMO-LUMO gap.     

DFT studies of CNT–functionalized uracil-acetate hybrids

Calculations based on density functional theory (DFT) have been performed to investigate the stabilities and properties of hybrid structures consisting of a molecular carbon nanotube (CNT) and uracil acetate (UA) counterparts. The investigated models have been relaxed to minimum energy structures and then various physical properties and nuclear magnetic resonance (NMR) properties have been evaluated. The results indicated the effects of functionalized CNT on the properties of hybrids through comparing the results of hybrids and individual structures. The oxygen atoms of uracil counterparts have been seen as the detection points of properties for the CNT–UA hybrids.     

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     

Au掺杂CNT吸附NO的第一性原理研究

碳纳米管(CNT)对于气体有超强的敏感性,可用于制备基于CNT的有害气体传感器.本文采用基于密度泛函理论的第一性原理研究Au掺杂CNT对NO和O_2的吸附特性.对吸附能、最终吸附距离、电荷转移量、态密度等的分析显示,Au掺杂使得CNT与NO间的交互作用明显增强,其中N原子端靠近CNT交互作用更强.禁带宽度和电荷密度分析表明,相比于NO分子中O原子端或者O2吸附,NO分子中N原子端与CNT发生交互作用会使体系导电性变化更为明显.说明Au掺杂能够很好地屏蔽空气中O_2对CNT导电性的影响,Au掺杂CNT作为NO气敏材料是可行的.     

Novel Cu–Cr alloy matrix CNT composites with enhanced thermal conductivity

Carbon nanotubes (CNTs) are incorporated into the Cu–Cr matrix to fabricate bulk CNT/Cu–Cr composites by means of a powder metallurgy method, and their thermal conductivity behavior is investigated. It is found that the formation of Cr₃C₂ interfacial layer improves the interfacial bonding between CNTs and Cu–Cr matrix, producing a reduction of interfacial thermal resistance, and subsequently enhancing the thermal conductivity of the composites. The thermal conductivity of the composites increases by 12 % and 17 % with addition of 5 vol.% and 10 vol.% CNTs, respectively. The experimental results are also theoretically analyzed using an effective medium approximation (EMA) model, and it is found that the EMA model combined with a Debye model can provide a satisfactory agreement to the experimental data.     

Microwave plasma CVD-grown graphene–CNT hybrids for enhanced electron field emission applications

The growth and electron emission characteristics were investigated from a hybrid structure of multiwalled carbon nanotubes (MWCNTs) and multilayer layer graphene (MLG) deposited on silicon substrate coated with iron catalyst and an interlayer of aluminium. The hybrid structures were synthesized in a two-step process by microwave plasma-enhanced chemical vapour deposition technique. The formation of MWCNTs takes place by absorption and precipitation of carbon radicals into the catalyst particles. Thereafter, ample carbon forms MLG on tip of the MWCNTs resulting in a MLG-MWCNTs hybrid nanostructure. MLG was observed to grow branching out of the tips and sidewalls of the MWCNTs and is expected to attach by Van der Walls bonds. Transmission electron microscopy and micro-Raman spectroscopy confirmed the crystalline nature of the hybrid structures. Electron emission studies were carried out using a diode-type field emission setup. The enhancement factor was found to be ~3,500 for bare MWCNTs, ~4,070 to ~5,000 for hybrid structures and ~6,500 for N-doped MLG-MWCNTs hybrid structures. Modification in the defects structure and enhancement of emission sites are suggested to be responsible for the increase of the field emission characteristics.     

Polythiophene encapsulated inside(13, 0) CNT: A nano-hybrid system

We present a first-principles calculation on the electronic and optical properties of a hybrid nanotube system consisting of a （13, 0） single-walled carbon nanotube encapsulated by polythiophene. This hybrid-system represents a complete new type of matter and is known as the peapod system. We analyze bow the polythiophene changes the electronic and optical properties of the nanotube. In particular, we examine new features in the dielectric function due to the transitions between the states of the polymer and the nanotube. The electronic structure of the combined system appears to be a simple superposition of the individual constituents. The density functional theory calculations demonstrate van der Waals interaction as the bonding mechanism between the tube and the encapsulated molecule.     

量子电容对CNT填充的屏蔽型TSV的传输性能影响研究

本文提出以苯并环丁烯(benzocyclobutene,BCB)或硅为介质层材料,用碳纳米管(Carbon Nanotube,CNT)填充的屏蔽型硅通孔(Shielded Through-Silicon Vias,S-TSV)结构,利用等效传输线模型计算了其正向传输系数和衰减常数,分析了量子电容(Quantum Capacitance,Cq)对S-TSV传输性能的影响。研究发现,Cq能改善以BCB为介质层,填充多壁碳纳米管束(Multi-walled carbon nanotube bundle,MWCNTB)的S-TSV高于20GHz频段的传输性能。此外,Cq可以明显提升以硅为介质层的S-TSV的传输性能,且Cq的温度效应能与硅电导的温度效应平衡,从而提高S-TSV的热稳定性。     

Electrochemical synthesis and lithium storage properties of three-dimensional porous Sn–Co alloy/CNT composite

Three-dimensional (3-D) porous copper with stable pore structure is prepared by electroless plating. 3-D porous Sn–Co alloy/carbon nanotube (CNT) composite is synthesized by electrodeposition using 3-D porous copper as the substrate. The scanning electron microscope results indicate that 3-D porous Sn–Co alloy/CNT composite contains a large amount of interconnected pores with the diameter size of ~3 μm. Upon cycling, the pore structure gradually disappears, but no serious exfoliation appears due to porous structure and reinforcement by CNT. The charge/discharge results demonstrate that the 3-D porous Sn–Co alloy/CNT composite electrode delivers high first reversible specific capacity of 490 mAh g^?1, and remains 441 mAh g^?1 after 60 cycles tested at different current densities. Even at the current density of 3,200 mA g^?1, the reversible specific capacity remains 319 mAh g^?1, which is 65 % of the first specific capacity cycled at the current density of 100 mA g^?1.     

The Young’s Modulus of a Zigzag CNT/Graphene Composite by Tension along the Graphene Direction

Physics of the Solid State - The Young’s modulus of a finite-sized zigzag carbon nanotube-based ribbon-like columnar graphene is theoretically studied. The dependence of elastic...     

The effect of concentration of <Emphasis Type="Bold">H</Emphasis> <Subscript> <Emphasis Type="Bold">2</Emphasis> </Subscript> physisorption on the current–voltage characteristic of armchair BN nanotubes in CNT–BNNT–CNT set

In this research, we have studied physisorption of hydrogen molecules on armchair boron nitride (BN) nanotube (3,3) using density functional methods and its effect on the current–voltage (I–V) characteristic of the nanotube as a function of concentration using Green’s function techniques. The adsorption geometries and energies, charge transfer and electron transport are calculated. It is found that H₂ physisorption can suppress the I–V characteristic of the BN nanotube, but it has no effect on the band gap of the nanotube. As the H₂ concentration increases, under the same applied bias voltage, the current through the BN nanotube first increases and then begins to decline. The current–voltage characteristic indicates that H₂ molecules can be detected by a BN-based sensor.     

Simulations on the mechanism of CNT bundle growth upon smooth and nanostructured Ni as well as <Emphasis Type="Italic">θ</Emphasis>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

In the current study, we have performed ab initio DFT calculations on the gradually growing 2D periodic models of capped single-wall carbon nanotubes (SW CNTs) upon their perpendicular junctions with the Ni(111) substrate, in order to understand the peculiarities of the initial stage of their growth on either smooth or nanostructured catalytic particles. Appearance of the adsorbed carbon atoms upon the substrate follows from the dissociation of CVD hydrocarbon molecules, e.g., CH₄: (CH₄)_ads → (CH)_ads+3H_ads and (CH)_ads → C_ads+H_ads. (Since the effective growth of CNTs upon Ni nanoparticles occur inside the nanopores of amorphous alumina, we have also simulated analogous surface reactions upon the θ-Al₂O₃(010) slabs). Association of the adsorbed carbon atoms upon the catalyst surface precedes further swelling of the (C_n)_ads islands after appearance of pentagonal defects within a honeycomb sheet which are more probable upon the catalyst surface containing either defects or nanoclusters (as in the case of the nanostructured substrate). The gradual growth of the capped CNTs is considerably more effective upon the nanostructured Ni(111) substrate compared to a smooth nickel substrate (cf. values of CNT adhesion energy per boundary C atom for chiralities of either armchair-type, 4.04 vs. 2.51 eV, or zigzag-type, 4.61 vs. 2.14 eV, respectively). The electronic charge transfer from the Ni catalyst towards the CNTs has been calculated for both chiralities (> 1 e per C atom), i.e., quite strong chemical bonds are formed within the CNT/Ni(111) interconnects.