石墨烯纳米带卷曲效应对其电子特性的影响

石墨烯纳米带 (GNRs) 是一种重要的纳米材料, 碳纳米管可看作是GNRs卷曲而成的无缝圆筒. 利用基于密度泛函理论的第一性原理方法, 系统研究了GNRs卷曲变形到不同几何构型时, 其电子特性, 包括能带结构 (特别是带隙) 、态密度、透射谱的变化规律. 结果表明: 无论是锯齿型GNRs (ZGNRs) 或扶手椅型GNRs (AGNRs), 在其卷曲成管之前, 其电子特性对卷曲形变均不敏感, 这意味着GNRs的电子结构及输运特性有较强地抵抗卷曲变形的能力. 当GNRs 卷曲成管后, ZGNRs和AGNRs表现出完全不同的性质, ZGNRs几乎保持金属性不变或变为准金属; 但AGNRs的电子特性有较大的变化, 出现不同带隙半导体、准金属之间的转变, 这也许密切关系到碳纳米管管口周长方向上的周期性边界条件及量子禁锢的改变. 这些研究对于了解GNRs电子特性的卷曲效应、以及GNRs与碳纳米管电子特性的关系 (结构与特性的关系) 有重要意义. 关键词： 石墨烯纳米带 卷曲效应 电子特性 密度泛函理论     

掺杂菱形BN片的石墨烯纳米带的电子特性

采用基于密度泛函理论的第一性原理方法,系统研究掺杂菱形BN片的石墨烯纳米带的电子特性.掺杂使扶手椅型石墨烯纳米带（AGNRs）的带隙增大,不同位置掺杂AGNRs的带隙大小略有差异.在无磁性态,无论是否掺杂,锯齿型石墨烯纳米带（ZGNRs）都为金属.在铁磁态,掺杂使ZGNRs由金属转变为半导体.而处于反铁磁态时,无论是否掺杂,ZGNRs都为半导体,掺杂使其带隙发生改变.掺杂的AGNRs和ZGNRs的结构稳定,掺杂ZGNRs的基态为反铁磁态.掺杂菱形BN片可以有效调控GNRs的电子特性.     

BN链掺杂的石墨烯纳米带的电学及磁学特性

基于密度泛函理论第一性原理系统研究了BN链掺杂石墨烯纳米带(GNRs)的电学及磁学特性, 对锯齿型石墨烯纳米带(ZGNRs)分非磁态(NM)、反铁磁态(AFM)及铁磁性(FM)三种情况分别进行考虑. 重点研究了单个BN链掺杂的位置效应. 计算发现: BN链掺杂扶手椅型石墨烯纳米带(AGNRs) 能使带隙增加, 不同位置的掺杂, 能使其成为带隙丰富的半导体. BN链掺杂非磁态ZGNR的不同位置, 其金属性均降低, 并能出现准金属的情况; BN链掺杂反铁磁态ZGNR, 能使其从半导体变为金属或半金属(half-metal), 这取决于掺杂的位置; BN链掺杂铁磁态ZGNR, 其金属性保持不变, 与掺杂位置无关. 这些结果表明: BN链掺杂能有效调控石墨烯纳米带的电子结构, 并形成丰富的电学及磁学特性, 这对于发展各种类型的石墨烯基纳米电子器件有重要意义. 关键词： 石墨烯纳米带 BN链掺杂 输运性质 自旋极化     

周期性纳米洞内边缘氧饱和石墨烯纳米带的电子特性

利用基于密度泛函理论的第一性原理方法,研究了内边缘氧饱和的周期性凿洞石墨烯纳米带（G NR）的电子特性. 研究结果表明：对于凿洞锯齿形石墨烯纳米带（ZGNRs）,在非磁性态时不仅始终为金属,且金属性明显增强;反铁磁态（AFM）时为半导体的ZGNR,凿洞后可能成为金属;但铁磁态（FM）为金属的ZGNR,凿洞后一般变为半导体或半金属. 而对于凿洞的扶手椅形石墨烯（AGNRs）,其带隙会明显增加. 深入分析发现：这是由于氧原子对石墨烯纳米带边的电子特性有重要的影响,以及颈次级纳米带（NSNR）及边缘次级纳米带（ESNR）的不同宽度及边缘形状（锯齿或扶手椅形）能呈现出不同的量子限域效应. 这些研究对于发展纳米电子器件有重要的意义. 关键词： 石墨烯纳米带 纳米洞 内边缘氧饱和 电子特性     

羟基饱和锯齿型石墨烯纳米带的电子结构

利用密度泛函理论,计算了羟基饱和锯齿型石墨烯纳米带(OH-ZGNRs)的相对稳定性和外加横向电场对其电子结构的影响.计算结果表明:OH-ZGNRs比氢饱和ZGNRs(H-ZGNRs)更为稳定,具有窄带隙自旋极化基态.此外,在外加横向电场作用下,OH-ZGNRs可实现半导体到半金属相转变. 关键词： 石墨烯纳米带 密度泛函理论 电场     

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.     

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     

金掺杂锯齿型石墨烯纳米带的电磁学特性研究

本文采用基于密度泛函理论的第一性原理计算了金原子填充锯齿型石墨烯纳米带 (ZGNRs)中双空位结构的电磁学特性. 计算结果表明: 边缘位置是金原子的最稳定掺杂位置, 杂质原子的引入导致掺杂边缘的磁性被抑制, 不过掺杂率足够大时, 掺杂边缘的磁性反而恢复了. 金掺杂纳米带的能带结构对掺杂率敏感: 随着掺杂率的增大, 掺杂纳米带分别表现半导体特性、半金属特性以及金属特性. 本文的计算表明金原子掺杂可以调制ZGNR的磁性以及能带特性, 为后续实验起指导作用, 有利于推动石墨烯材料在自旋电子学方面的应用.     

扶手椅型C3B纳米带:结构稳定性、电子特性及调控效应

单层C₃B是典型的类石墨烯二维材料,已在实验上成功制备.采用密度泛函理论方法(DFT)研究了扶手椅型单层C₃B纳米带的结构稳定性、电子性质及物理调控效应,计算结果表明:对于裸边纳米带,如果带边缘全由C原子组成(AA型),则电子相为半导体;两个带边缘均由C与B原子混合组成时(BB型),则纳米带的电子相为金属;而纳米带的一边由C原子组成、另一边由B与C原子混合构成(AB型),则纳米带的电子相为金属.这说明纳米带边缘的B原子对于纳米带成为金属或半导体起决定作用.而对于H端接的纳米带,它们全部为直接或间接带隙半导体.H端接的纳米带载流子迁移率一般比裸边纳米带低,这与它们较大的有效质量及较高的形变势有密切关系.同时发现半导体性质的纳米带对物理调控非常敏感,特别是在压应变和外电场作用下,纳米带的带隙明显变小,这有利于对光能的吸收和研发光学器件.     

Rb吸附石墨烯纳米带电子性质和光学性质的研究

本文基于密度泛函理论的第一性原理方法了计算了Rb、O和H吸附石墨烯纳米带的差分电荷密度、能带结构、分波态密度和介电函数,调制了石墨烯纳米带的电子性质和光学性质,给出了不同杂质影响材料光学特性的规律.结果表明本征石墨烯纳米带为n型直接带隙半导体且带隙值为0.639 eV;Rb原子吸附石墨烯纳米带之后变为n型简并直接带隙半导体,带隙值为0.494eV;Rb和O吸附石墨烯纳米带变为p型简并直接带隙半导体,带隙值增加为0.996eV;增加H吸附石墨烯纳米带后,半导体类型变为n型直接带隙半导体,且带隙变为0.299eV,带隙值相对减小,更有利于半导体发光器件制备.吸附Rb、O和H原子后,石墨烯纳米带中电荷密度发生转移,导致C、Rb、O和H之间成键作用显著.吸附Rb之后,在费米能级附近由C-2p、Rb-5s贡献;增加O原子吸附之后,O-2p在费米能级附近贡献非常活跃,杂化效应使费米能级分裂出一条能带;再增加H原子吸附之后,Rb-4p贡献发生蓝移,O-2p在费米能级附近贡献非常强,费米能级分裂出两条能带.Rb、O和H的吸附后,明显调制了石墨烯纳米带的光学性质.     

Atomic and electronic structures of divacancy in graphene nanoribbons

First principles calculations have been performed to investigate the electronic structures and transport properties of defective graphene nanoribbons (GNRs) in the presence of pentagon-octagon-pentagon (5-8-5) defects. Electronic band structure results reveal that 5-8-5 defects in the defective zigzag graphene nanoribbon (ZGNR) is unfavorable for electronic transport. However, such defects in the defective armchair graphene nanoribbon (AGNR) give rise to smaller band gap than that in the pristine AGNR, and eventually results in semiconductor to metal-like transition. The distinct roles of 5-8-5 defects in two kinds of edged-GNR are attributed to the different coupling between π^? and π subbands influenced by the defects. Our findings indicate the possibility of a new route to improve the electronic transport properties of graphene nanoribbons via tailoring the atomic structures by ion irradiation.     

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.     

Edge-modified zigzag-shaped graphene nanoribbons: Structure and electronic properties

Control of the band gap of graphene nanoribbons is an important problem for the fabrication of effective radiation detectors and transducers operating in different frequency ranges. The periodic edge-modified zigzag-shaped graphene nanoribbon (GNR) provides two additional parameters for controlling the band gap of these structures, i.e., two GNR arms. The dependence of the band gap E _g on these parameters is investigated using the π-electron tight-binding method. For the considered nanoribbons, oscillations of the band gap E _g as a function of the nanoribbon width are observed not only in the case of armchair-edge graphene nanoribbons (as for conventional graphene nanoribbons) but also for zigzag GNR edges. It is shown that the change in the band gap E _g due to the variation in the length of one GNR arm is several times smaller than that due to the variation in the nanoribbon width, which provides the possibility for a smooth tuning of the band gap in the energy spectrum of the considered graphene nanoribbons.     

含单排线缺陷锯齿型石墨烯纳米带的电磁性质

基于密度泛函理论的第一性原理方法,研究了含单排线缺陷锯齿型石墨烯纳米带(ZGNR)的电磁性质,主要计算了该缺陷处于不同位置时的能带结构、透射谱、自旋极化电荷密度、总能以及布洛赫态.研究表明,含单排线缺陷的ZGNR和无缺陷的ZGNR在非磁性态和铁磁态下都为金属.虽然都为金属,但其呈金属性的成因有差异.在反铁磁态下,单排线缺陷越靠近ZGNR的边缘,对ZGNR电磁性质的影响越明显,缺陷由ZGNR对称轴线向边缘移动过程中,含单排线缺陷的ZGNR有一个半导体-半金属-金属的相变过程.虽然线缺陷靠近中线的ZGNR为半导体,但由于缺陷引入新的能带,导致含单排线缺陷的ZGNR的带隙小于无缺陷ZGNR的带隙.单排线缺陷紧邻边界时,含缺陷ZGNR最稳定;单排线缺陷位于次近邻边界位置时,含缺陷ZGNR最不稳定.在反铁磁态下,对单排线缺陷位于对称轴线的ZGNR施加适当的横向电场,可以实现半导体到半金属的转变.这些研究结果对于发展基于石墨烯的纳米电子器件有重要的意义.     

Electronic properties of Li-doped zigzag graphene nanoribbons

Zigzag graphene nanoribbons (ZGNRs) are known to exhibit metallic behavior. Depending on structural properties such as edge status, doping and width of nanoribbons, the electronic properties of these structures may vary. In this study, changes in electronic properties of crystal by doping Lithium (Li) atom to ZGNR structure are analyzed. In spin polarized calculations are made using Density Functional Theory (DFT) with generalized gradient approximation (GGA) as exchange correlation. As a result of calculations, it has been determined that Li atom affects electronic properties of ZGNR structure significantly. It is observed that ZGNR structure exhibiting metallic behavior in pure state shows half-metal and semiconductor behavior with Li atom.     

Electronic transport of graphene nanoribbons within recursive Green’s function

In this work, we introduce a recursive Green’s function method for investigating electronic transport in a graphene nanoribbons (GNRs) quantum wire with armchair (AGNR) and zigzag (ZGNR) edges which attached to two semi-infinite square lattice leads. This model reduces numerical calculations time and enables us to use Green’s function method to investigate transport in a supperlattice device. Therefore, we consider AGNR and ZGNR devices attached to metallic semi-infinite square lattice leads, taking into account the effects of longitudinal and wide of the wire. Our calculations are based on the tight-binding model, which the recursive Green’s function method is used to solve inhomogeneous differential equations. We concentrate on the electrical conductance and current for various length and wide size of the wire. Our numerical results show that the transport properties are strongly affected by the quantum interference effect and the lead interface geometry to the device. By controlling the type of contact and wire geometry, this kind of system can explain the antiresonance states at the Fermi energy. Our results can serve as a base for developments in designing nano-electronic devices.     

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