双空位缺陷石墨纳米带的电子结构和输运性质研究

基于第一原理电子结构和输运性质计算,研究了585双空位拓扑缺陷对锯齿（zigzag）型石墨纳米带（具有椅型（armchair）边）电子结构和输运性质的影响.研究发现,585双空位缺陷的存在使得锯齿型石墨纳米带的能隙增大,并在能隙中出现了一条局域于缺陷处的缺陷态能带,双空位缺陷的取向也影响其能带结构.另外,585双空位缺陷对能隙较小的锯齿型石墨纳米带输运性质的影响较大,而对能隙较大的锯齿型石墨纳米带影响很小,缺陷取向并不显著影响纳米带的输运性质. 关键词： 石墨纳米带 585空位缺陷 电子结构 输运性质     

单空位缺陷对石墨纳米带电子结构和输运性质的影响

基于第一性原理电子结构和输运性质计算,研究了单空位缺陷对单层石墨纳米带(包括zigzag型和armchair型带)电子性质的影响.研究发现,单空位缺陷使石墨纳米带在费米面上出现一平直的缺陷态能带;单空位缺陷的引入使zigzag型半导体性的石墨纳米带变为金属性,这在能带工程中有重要的应用价值;奇数宽度的armchair型石墨纳米带表现出金属特性,有着很好的导电性能,同时,偶数宽度的armchair型石墨带虽有金属性的能带结构,但却有类似半导体的伏安特性;单空位缺陷使得奇数宽度的armchair石墨纳米带导电 关键词： 石墨纳米带 单空位缺陷 电子结构 输运性质     

Zigzag型石墨纳米带电子结构和输运性质的第一性原理研究

采用第一性原理电子结构和输运性质计算研究了zigzag型单层石墨纳米带(具有armchair 边缘)的电子结构和输运性质及其边缘空位缺陷效应. 研究发现,完整边缘的zigzag型石墨纳米带是具有一定能隙的半导体带,边缘空位缺陷的存在使得纳米带能隙变小,且缺陷浓度越大,能隙越小,并发生了半导体-金属转变. 利用这些研究结果,将有助于在能带工程中实现其电子结构裁剪. 关键词： 石墨纳米带 空位缺陷 电子结构 输运性质     

Zigzag型石墨纳米带电子结构和输运性质的第一性原理研究

采用第一性原理电子结构和输运性质计算研究了zigzag型单层石墨纳米带(具有armchair 边缘)的电子结构和输运性质及其边缘空位缺陷效应. 研究发现，完整边缘的zigzag型石墨纳米带是具有一定能隙的半导体带，边缘空位缺陷的存在使得纳米带能隙变小，且缺陷浓度越大，能隙越小，并发生了半导体-金属转变. 利用这些研究结果，将有助于在能带工程中实现其电子结构裁剪.     

基于分子动力学的石墨炔纳米带空位缺陷的导热特性

空位缺陷石墨炔比完整石墨炔更贴近实际材料,而空位缺陷的多样性可导致更丰富的导热特性,因此模拟各种空位缺陷对热导率的影响显得尤为重要.采用非平衡分子动力学方法,通过在纳米带长度方向上施加周期性边界条件,基于AIREBO(adaptive intermolecular reactive empirical bond order)势函数描述碳-碳原子间的相互作用,模拟了300 K时单层石墨炔纳米带乙炔链上单空位缺陷和双空位缺陷以及苯环上单空位缺陷对其热导率的影响,利用Fourier定律计算热导率.模拟结果表明,对于几十纳米尺度范围内的石墨炔纳米带热导率,1)由于声子的散射集中和声子倒逆过程增强,与完美无缺陷的石墨炔纳米带相比,空位缺陷会导致石墨炔纳米带热导率的下降;2)由于声子态密度匹配程度高低的不同,相比于乙炔链上的空位缺陷,苯环的空位缺陷对石墨炔纳米带热导率影响更大,乙炔链上空位缺陷数量对石墨炔纳米带热导率的影响明显;3)由于尺寸效应问题,随着长度增加,石墨炔纳米带热导率会相应增大.本文的研究可为在一定尺度下进行石墨炔纳米带热导率的调控问题提供参考.     

单空位缺陷诱导的扶手椅型石墨烯纳米带电学性能的转变

本文基于密度泛函理论的第一性原理计算了单空位缺陷对 扶手椅型石墨烯纳米带电学特性的影响. 计算结果表明: 当单空位位于纳米带边缘位置时, 系统结构最稳定. 不同位置上单空位缺陷的引入都会使得原本为半导体的本征 扶手椅型石墨烯纳米带变成金属性; 随着单空位浓度的减小, 其对纳米带能带结构的影响逐渐减弱; 随着纳米带宽度的增大, 表征其金属性的特征值表现出震荡性的减弱. 单空位缺陷诱导的扶手椅型纳米带的半导体特性到金属特性的转变为石墨烯在 电子器件中的应用提供了理论指导. 关键词： 扶手椅型石墨烯纳米带 单空位缺陷 电学性能     

铂掺杂扶手椅型石墨烯纳米带的电学特性研究

本文采用基于密度泛函理论(DFT)的第一性原理计算了铂原子填充扶手椅型石墨烯纳米带(AGNR)中双空位结构的电学性能.计算结果表明: 通过控制铂原子的掺杂位置, 可以实现纳米带循环经历小带隙半导体—金属—大带隙半导体的相变过程; 纳米带边缘位置是铂原子掺杂的最稳定位置, 边缘掺杂纳米带的带隙值随宽度的变化与本征AGNR一样可用三簇曲线表示, 但在较大宽度时简并成两条曲线, 一定程度上抑制了带隙值的振荡; 并且铂原子边缘掺杂导致宽度系数N_a = 3p和3p + 1(p是一个整数)的几个较窄纳米带的带隙中出现杂质能级, 有效地降低了其过大的带隙值. 此外, 铂掺杂AGNR的能带结构对掺杂浓度不是很敏感, 从而降低了对实验精度的挑战. 本文的计算有利于推动石墨烯纳米带在纳米电子学方面的应用.     

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.     

锯齿型石墨纳米带叠层复合结的电子输运

基于紧束缚格林函数方法,研究了两半无限长锯齿型石墨纳米带叠层复合结的电子输运性质.结果表明,层间次近邻相互作用、叠层区长度及门电压对复合结的电子透射谱有重要调制作用.层间次近邻相互作用导致复合结的透射谱关于费米能呈现非对称性,与实验结果很好相符.低于费米能第一子能区内周期性出现透射系数为0和1的台阶,呈现全反射与透射现象.随散射结长度增加,透射系数在1内周期性振荡,呈现明显的量子干涉效应.在门电压调控下,低于费米能的透射系数出现了从1到0的转变,类似于开关效应.相关结果对基于石墨烯器件的设计与应用有指导意义.     

含Stone-Wales缺陷zigzag型石墨烯纳米带的电学和光学性能研究

本文采用基于密度泛函理论的第一性原理对zigzag型石墨烯纳米带中含有不同Stone-Wales缺陷的电子结构特性和光学性能进行研究. 考虑了两种模型:不计电子自旋和考虑电子自旋的情况.研究发现:不计电子自旋情况下,含对称Stone-Wales缺陷的石墨烯纳米带在缺陷区域出现了凹凸不平的折皱构型,两种不同的Stone-Wales缺陷都引起了电荷的重新分布.考虑电子自旋时,Stone-Wales缺陷的引入对石墨烯纳米带自旋密度有显著影响,也引起了不同自旋的电子态密度的变化.进一步研究了纳米带的光学性能,发现 关键词： 石墨烯纳米带 Stone-Wales缺陷 电子结构 光学性能     

A-Z-A型石墨烯场效应晶体管吸附 效应的第一性原理研究

利用第一性原理的计算方法, 研究了A-Z-A型GNR-FET的电子结构和输运性质及其分子吸附效应. 得到了以下结论: 纯净的A-Z-A型GNR-FET具有典型的双极型晶体管特性, 吸附分子的存在会使纳米带能隙变小. 对于吸附H, H₂, H₂O, N₂, NO, NO₂, O₂, CO₂和SO₂分子的情况, A-Z-A型GNR-FET仍然保持着场效应晶体管的基本特征, 但吸附不同类型的分子会使GNR-FET的输运特性发生不同程度的改变; 对于吸附OH分子的情况, 输运特性发生了本质的改变, 完全不具有场效应晶体管的特性. 这些研究结果将有助于石墨烯气体探测器的工程实现, 并对应用于不同环境中GNR-FET的设计具有重要指导意义.     

The complex band structure for armchair graphene nanoribbons

Using a tight binding transfer matrix method,we calculate the complex band structure of armchair graphene nanoribbons.The real part of the complex band structure calculated by the transfer matrix method fits well with the bulk band structure calculated by a Hermitian matrix.The complex band structure gives extra information on carrier’s decay behaviour.The imaginary loop connects the conduction and valence band,and can profoundly affect the characteristics of nanoscale electronic device made with graphene nanoribbons.In this work,the complex band structure calculation includes not only the first nearest neighbour interaction,but also the effects of edge bond relaxation and the third nearest neighbour interaction.The band gap is classified into three classes.Due to the edge bond relaxation and the third nearest neighbour interaction term,it opens a band gap for N=3M 1.The band gap is almost unchanged for N=3M + 1,but decreased for N=3M.The maximum imaginary wave vector length provides additional information about the electrical characteristics of graphene nanoribbons,and is also classified into three classes.     

Magnetoconductance of graphene nanoribbons

The electronic and transport properties of monolayer and AB-stacked bilayer zigzag graphene nanoribbons subject to the influences of a magnetic field are investigated theoretically. We demonstrate that the magnetic confinement and the size effect affect the electronic properties competitively. In the limit of a strong magnetic field, the magnetic length is much smaller than the ribbon width, and the bulk electrons are confined solely by the magnetic potential. Their properties are independent of the width, and the Landau levels appear. On the other hand, the size effect dominates in the case of narrow ribbons. In addition, the dispersion relations rely sensitively on the interlayer interactions. Such interactions will modify the subband curvature, create additional band-edge states, change the subband spacing or the energy gap, and separate the partial flat bands. The band structures are symmetric or asymmetric about the Fermi energy for monolayer or bilayer nanoribbons, respectively. The chemical-potential-dependent electrical and thermal conductance exhibits a stepwise increase behaviour. The competition between the magnetic confinement and the size effect will also be reflected in the transport properties. The features of the conductance are found to be strongly dependent on the field strength, number of layers, interlayer interactions, and temperature.     

Electronic transport for armchair graphene nanoribbons with a potential barrier

This paper studies the electronic transport property through a square potential barrier in armchair-edge graphene nanoribbon (AGNR). Using the Dirac equation with the continuity condition for wave functions at the interfaces between regions with and without a barrier, we calculate the mode-dependent transmission probability for both semiconducting and metallic AGNRs, respectively. It is shown that, by some numerical examples, the transmission probability is generally an oscillating function of the height and range of the barrier for both types of AGNRs. The main difference between the two types of systems is that the magnitude of oscillation for the semiconducting AGNR is larger than that for the metallic one. This fact implies that the electronic transport property for AGNRs depends sensitively on their widths and edge details due to the Dirac nature of fermions in the system.     

The electronic transport properties of defected bilayer sliding armchair graphene nanoribbons

By applying non-equilibrium Green's functions (NEGF) in combination with tight-binding (TB) model, we investigate and compare the electronic transport properties of perfect and defected bilayer armchair graphene nanoribbons (BAGNRs) under finite bias. Two typical defects which are placed in the middle of top layer (i.e. single vacancy (SV) and stone wale (SW) defects) are examined. The results reveal that in both perfect and defected bilayers, the maximum current refers to β-AB, AA and α-AB stacking orders, respectively, since the intermolecular interactions are stronger in them. Moreover it is observed that a SV decreases the current in all stacking orders, but the effects of a SW defect is nearly unpredictable. Besides, we introduced a sequential switching behavior and the effects of defects on the switching performance is studied as well. We found that a SW defect can significantly improve the switching behavior of a bilayer system. Transmission spectrum, band structure, molecular energy spectrum and molecular projected self-consistent Hamiltonian (MPSH) are analyzed subsequently to understand the electronic transport properties of these bilayer devices which can be used in developing nano-scale bilayer systems.     

N掺杂对zigzag型石墨烯纳米带的能带结构和输运性质的影响

用第一性原理研究了N掺杂zigzag型石墨烯纳米带(z-GNRs)的能带结构、透射谱和电流电压特性,研究结果表明N掺杂将使得z-GNRs的能带结构中出现能隙,材料从金属转变为半导体;随着杂质浓度的增大,相同偏压下电流明显减小,同时体系费米面附近的透射率逐渐减小;z-GNRs的长度、宽度以及N原子的替代掺杂位置均会对输运性质产生影响,在宽度较小的情况下,掺杂浓度和掺杂位置两种因素共同影响体系的输运性质. 关键词： 石墨烯纳米带 N掺杂 能带结构 输运性质