手性环状碳纳米管的电子结构及磁化特性

基于石墨平面π电子的紧束缚模型,导出了手性(chiral)环状碳纳米管(TCNTs)在磁场中的电子结构,从而对TCNTs量子特性和磁化规律进行了较深入研究.第Ⅰ,Ⅱ类TCNTs在磁场中存在金属—半导体的连续转变.计算分析表明:在T=0K时,第Ⅰ,Ⅱ类TCNTs的磁化强度随磁通量Φ呈线性周期性变化(以磁通量子Φ₀=h/e为周期),并且磁化强度对手性角θ、管口半径r,以及温度T极为敏感,但与环半径R无关.手性TCNTs的磁化强度比椅形或锯齿形TCNTs的磁化强度强很多;而第Ⅲ类TCNTs 关键词： 手性环状碳纳米管 电子结构 磁化特性     

锯齿型单壁碳纳米管能隙的第一性原理研究

本文采用基于广义梯度近似(GGA)的第一性原理方法,对锯齿型单壁碳纳米管(7,0)、(8,0)、(9,0)、(12,0)的能带结构和能隙进行理论计算.结果表明,各孤立管能隙值跟紧束缚(TB)近似所推出的结论有很大的出入,但跟实验观测结果比较接近.本文对引起这一差异的原因做了初步探讨.     

锯齿型单壁碳纳米管的广义层错能计算

基于密度泛函理论的第一性原理方法,计算了两种不同半径的锯齿型单壁碳纳米管以及单层石墨的广义层错能曲线。对小位移处广义层错能曲线进行斜率拟合所得切变模量与其它文献值一致。对三条广义层错能曲线的对比可知,锯齿型碳纳米管与单层石墨的广义层错能曲线相近,锯齿型单壁碳纳米管的曲率效应不明显。     

磁场中碳纳米管电子结构的紧束缚法研究

利用石墨平面碳原子轨道作sp2杂化时π电子的紧束缚模型,对磁场中直状单层碳纳米管(SWNTs)的电子结构进行理论推导和分析。磁场对碳纳米管的波矢产生影响,从而使碳纳米管的电子结构及能隙均以磁通量子Φ0(=h/e)为周期随磁通量Φ周期性变化。     

氮掺杂手性碳纳米管的电子结构和输运特性的理论研究

运用第一性原理的密度泛函理论,结合非平衡格林函数,研究了氮原子取代掺杂手性单壁(6,3)碳纳米管的电子结构和输运特性.计算结果表明:不同构形和不同数目的氮原子取代掺杂对手性碳管的输运性质有很复杂的影响.研究发现,氮原子掺杂明显改变了碳管的电子结构,使金属型手性碳管的输运性能降低,电流-电压曲线呈非线性变化,而且输运性能随着杂质原子间间距的变化而发生显著改变.在一定条件下,金属型碳管向半导体型转变. 关键词： 手性单壁碳纳米管 氮掺杂 电子结构 输运性能     

接枝羧基的有限长碳纳米管电子结构的第一性原理研究

基于局域密度泛函理论，采用第一性原理方法，建立了对(5,5)型和(9,0)型有限长碳纳米管接枝羧基官能团的原子模型，通过计算其电子分布和态密度的变化，讨论羧基官能团对碳纳米管电子结构和电子输运特性的影响. 计算表明，接枝羧基的碳纳米管,其电子结构明显改变，其费米能级上的电子态密度下降；最高占据轨道上的非定域程度减弱,致使电子输运性能呈下降趋势. 关键词： 碳纳米管 密度泛函理论 电子结构     

堆叠石墨片对锯齿型石墨纳米带电子输运的影响

采用格林函数方法研究了堆叠石墨片对锯齿型石墨纳米带电子输运性质的影响,计算了两种不同堆叠方式下锯齿型石墨纳米带的电导.研究发现,由于堆叠石墨片与石墨纳米带的耦合作用,锯齿型石墨纳米带的电导谱出现了电导谷.在远离费米能处,两种堆叠方式下的电导谷位置相近甚至重合;而在费米能附近,两种堆叠方式下的电导谷存在差异.此外,讨论了堆叠石墨片的几何尺寸对锯齿型石墨纳米带电子输运的影响.结果显示,随石墨片几何尺寸的增大,锯齿型石墨纳米带在两种堆叠方式下远离费米能处的电导谷逐渐向费米能方向移动,同时其费米能附近的电导谷在两种堆叠方式下的差异随石墨片尺寸的增大变得更为明显.研究结果表明,堆叠石墨片能够有效地调制锯齿型石墨纳米带的电子输运性质.     

单壁碳纳米管能带及其电子特性研究

从能带理论出发,采用电子紧束缚能量色散关系,推导锯齿,扶手椅和手性单壁碳纳米管(SWCNT)的电子能带结构表达式,指出单壁碳纳米管或为金属或为半导体的判据。结果表示:单壁碳纳米管的电子结构与其几何结构密切相关,如扶手椅型单壁碳纳米管是金属性的,而对其它类型的单壁碳纳米管是与碳纳米管的手性指数有关,只有手性指数n和m的差别等于3的倍数时,单壁碳纳米管是金属性的,否则会显出有带隙的半导体特性。这意味着单壁碳纳米管是由特殊的电子传输和光学性质,在纳米电子学领域具有巨大的潜在应用价值。     

单壁碳纳米管中的电子波函数

金属能带理论告诉我们 ,如果金属材料具有完善的周期结构 ,并排除了任何化学无序 ,那么电子在其中的传播将不受散射 .而实际上 ,金属不可能达到上述理想状态 ,即使在亚微米尺度上 ,人们也难于观察到无散射的电子弹道输运 .理论曾经预言 ,在长度微米量级的金属性单壁碳纳米管 (ＳＷＮＴ)中 ,电子能态具有区别于大块金属的某些特征 .于是 ,连接两个电极的ＳＷＮＴ ,就像是一根柔性的电子波导 ,允许不同波长的电子波在其中相干叠加 ,并以弹道的方式传播 .随着传统电子器件尺寸的日益减小 ,传输电流与导线中原子间的相互作用不能再被忽略 ,这一…     

嵌入锂原子的zigzag型单壁碳纳米管的电子传导特性

运用基于第一性原理的密度泛函理论（DFT）的非平衡格林函数（NEGF）方法对Li原子嵌入后的zigzag型单壁碳纳米管(SWCNT)的电子输运性质进行了研究.在构建和优化了Li原子嵌入的zigzag型单壁碳纳米管的电子输运模型后,研究了该系统的电子传输概率、能态密度、电子透射谱,还研究了电子能量和偏置电压设置与变化对其电子输运特性的影响.结果显示zigzag型单壁碳纳米管嵌入Li原子后,电子输运特性发生了较大变化,具有电子输运拓宽效应和量子台阶复苏效应. 关键词： Li原子 碳纳米管 电子输运 拓宽效应     

Structural stability and electronic properties of carbon star lattice monolayer

By means of the first-principles calculations, we have investigated the structural stability and electronic properties of carbon star lattice monolayer and nanoribbons. The phase stability of the carbon star lattice is verified through phononmode analysis and room temperature molecular dynamics simulations. The carbon star lattice is found to be metallic due to the large states across the Fermi-level contributed by pz orbital. Furthermore, the nanoribbons are also found to be metallic and no spin polarization occurs, except for the narrowest nanoribbon with one C12 ring, which has a ferromagnetic ground state. Our results show that carbon star lattice monolayer and nanoribbons have rich electronic properties with great potential in future electronic nanodevices.     

Structural and electronic properties of carbon nanotubes under hydrostatic pressures

We studied the structural and electronic properties of carbon nanotubes under hydrostatic pressures based on molecular dynamics simulations and first principles band structure calculations. It is found that carbon nanotubes experience a hard-to-soft transition as external pressure increases. The bulk modulus of soft phase is two orders of magnitude smaller than that of hard phase. The band structure calculations show that band gap of (10, 0) nanotube increases with the increase of pressure at low pressures. Above a critical pressure (5.70GPa), band gap of (10, 0) nanotube drops rapidly and becomes zero at 6.62GPa. Moreover, the calculated charge density shows that a large pressure can induce an {sp}²-to-{sp}³ bonding transition, which is confirmed by recent experiments on deformed carbon nanotubes.     

单壁碳纳米管电子输运特性的稳定性分析

基于变形单壁碳纳米管能量色散关系,计算了碳纳米管最低导带的电子速度及有效质量随形变系数变化的各种曲线,以此推测碳纳米管输运性质的稳定性问题.计算结果表明：对于特定类型的碳纳米管,只当其形变发生在某特定方向、且处于低形变（形变系数ε≤002 ）区时,电子平均速度v_mean及平均有效质量m^*_mean随形变改变才会很小（相对改变量≤2%）,这意味着此时的碳纳米管低偏压电子输运性能是基本稳定的.而其他形变情形,电子平均速度v_mean或电子平均有效质量m^*_mean或两者随形变变化明显,甚至有跃变,这意味着其低偏压电子输运性能是不稳定的,甚至极不稳定. 关键词： 变形单壁碳纳米管 电子速度 电子有效质量 输运性能稳定性     

Low-energy electronic properties of pairs of identical carbon nanotubes

The tight-binding model is employed to study the low-energy electronic properties of aligned pairs of identical single-wall carbon nanotubes with the intertube interactions. The rotational symmetry about the tube axes is totally broken, and the intertube interactions hybridize the atomic states on each tube to create new sub-bands. Sub-band spacing, sub-band curvature, band-edge states, and energy gaps are sensitive to stacking types and are also dependent on the radius and the chirality of the tubes. The systems could be metal, semimetal, or semiconductor depending on their stacking types. In particular, an armchair pair keeps the band structures linear like a single tube if the pair has a glide symmetry with respect to the plane between its constituent tubes. Breaking this symmetry makes the pair semimetallic or semiconducting. However, there are no such properties for chiral and zigzag pairs. The variations in electronic structures of these pairs are more complicated and more sensitive to the tube radii. Instead of being like a rope or a large bundle, the stacking-type dependent behavior is more similar to commensurate double-wall carbon nanotubes.     

Electronic properties of multi-defected zigzag carbon nanotubes

Electronic properties of multi-defected zigzag single-walled carbon nanotubes are investigated by use of the tight-binding Green's function method. The Stone-Wales defects and the vacancies are considered. We find that the conductance sensitively depends on the realistic defect configurations for the metallic zigzag carbon nanotubes. Interestingly, the electronic transport properties of the nanotubes with three vacancies can be considered as the sum effect of two double-vacancies, while those with Stone-Wal...     

Variation of the electronic properties of zigzag boron nitride nanotubes by Al-doping: a DFT study

Boron nitride nanotubes (BNNTs) are semiconductors with a wide band gap. In comparison with carbon nanotubes (CNTs), BNNTs have higher chemical stability, excellent mechanical properties and higher thermal conductivity. In this paper, we study the effect of diameters and substituting B and N atoms of various zigzag BNNTs with Al, on structural and electronic properties of BNNTs in solid state using the density functional theory method. The results of calculations of density of states and band structure (band) showed that the band gap between the valence and conduction level increases as a result of the enhancement of tube diameter of BNNTs. Finally, the results showed that the electronic properties of the pristine BNNTs can be improved by doping Al atom in the zigzag configuration of tubes.     

Structural and electronic properties of chiral single-wall copper nanotubes

The structural,energetic and electronic properties of chiral(n,m)(3≤n≤6,n/2≤m≤n)single-wall copper nanotubes(CuNTs)have been investigated by using projector-augmented wave method based on density-functional theory.The(4,3)CuNT is energetically stable and should be observed experimentally in both free-standing and tip-suspended conditions,whereas the(5,5)and(6,4)CuNTs should be observed in free-standing and tip-suspended conditions,respectively.The number of conductance channels in the CuNTs does not always correspond to the number of atomic strands comprising the nanotube.Charge density contours show that there is an enhanced interatomic interaction in CuNTs compared with Cu bulk.Current transporting states display different periods and chirality,the combined effects of which lead to weaker chiral currents on CuNTs.     

Structural and vibrational properties of deformed carbon nanotubes

The fantastic variation of the physical properties of carbon nanotubes (CNTs) and their bundles under mechanical strain and hydrostatic pressure makes them promising materials for fabricating nanoscale electromechanical coupling devices or transducers. In this paper, we review the recent progress in this field, with much emphasis on our first-principles numerical studies on the structural and vibrational properties of the deformed CNTs under uniaxial and torsional strains, and hydrostatic pressure. The nonresonant Raman spectra of the deformed CNTs are also introduced, which are calculated by the first-principles calculations and the empirical bond polarizability model.