锯齿型石墨烯纳米带的能带研究

运用π电子紧束缚模型,具体研究了锯齿型石墨烯纳米带(ZGNRs)的边界结构对能带,特别是费米面附近的导带和价带电子的影响.计算了七种不同边界结构的ZGNRs的能带色散关系及费米面附近价带电子在原胞中各原子上的分布情况.计算结果表明:两边界都无悬挂原子的NN-ZGNRs,只有一边界有悬挂原子的DN-ZGNRs,两边界都有五边形环的SPP-ZGNRs和ASPP-ZGNRs为金属性.两边界都有悬挂原子的DD-ZGNRs,一边界为五边形环另一边界无悬挂原子的PN-ZGNRs和一边界为五边形环另一边界有悬挂原子的P 关键词： 锯齿型石墨烯纳米带 紧束缚模型 电子密度分布 缺陷结构     

掺杂三角形硼氮片的锯齿型石墨烯纳米带的磁电子学性质

利用基于密度泛函理论的第一性原理方法,研究了三角形BN片掺杂的锯齿型石墨烯纳米带(ZGNR)的磁电子学特性.研究表明:当处于无磁态时,不同位置掺杂的ZGNR都为金属;当处于铁磁态时,随着杂质位置由纳米带的一边移向另一边时,依次可以实现自旋金属-自旋半金属-自旋半导体的变化过程,且只要不在纳米带的边缘掺杂,掺杂的ZGNR就为自旋半金属;当处于反铁磁态时,在中间区域掺杂的ZGNR都为自旋金属,而在两边缘掺杂的ZGNR没有反铁磁态.掺杂ZGNR的结构稳定,在中间区域掺杂时反铁磁态是基态,而在边缘掺杂时铁磁态为基态.研究结果对于发展基于石墨烯的纳米电子器件具有重要意义.     

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.     

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.     

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     

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     

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.     

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     

边缘重构对锯齿型石墨烯纳米带电子输运的影响

实验研究表明石墨烯纳米带中广泛地存在边缘结构重构且稳定的边缘缺陷结构.本文采用第一性原理的计算方法研究了锯齿型石墨烯纳米带中边缘结构重构形成的两种不同缺陷结构对材料电子输运性能的影响.研究发现两种缺陷边缘结构对稳定纳米尺度位型结构和电子能带结构具有显著影响,它使得费米能级发生移动并引起了共振背散射.两种边缘缺陷重构均抑制了费米能级附近电子输运特性并导致不同区域的电子完全共振背散射,电导的抑制不仅与边缘缺陷结构的大小有关,它更取决于边缘缺陷重构位型引起的缺陷态的具体分布和电子能带的移动.     

Edge magnetization in Bernal-stacked trilayer zigzag graphene nanoribbons

We have used a tight-binding Hamiltonian of an ABA-stacked trilayer zigzag graphene nanoribbon with β-alignment edges to study the edge magnetizations. Our model includes the effect of the intralayer next-nearest-neighbor hopping, the interlayer hopping responsible for the trigonal warping and the interaction between electrons, which is considered by a single band Hubbard model in the mean field approximation. Firstly, in the neutral system we analyzed the two magnetic states in which both edge magnetizations reach their maximum value; the first one is characterized by an intralayer ferromagnetic coupling between the magnetizations at opposite edges, whereas in the second state that coupling is antiferromagnetic. The band structure, the location of the edge-state bands and the local density of states resolved in spin are calculated in order to understand the origins of the edge magnetizations. We have also introduced an electron doping so that the number of electrons in the ribbon unit cell is higher than in neutral case. As a consequence, we have obtained magnetization steps and charge accumulation at the edges of the sample, which are caused by the edge-state flat bands.     

Band structure and edge states of star-like zigzag graphene nanoribbons

Connecting three zigzag graphene nanoribbons(ZGNRs) together through the sp~3 hybrid bonds forms a star-like ZGNR(S-ZGNR). Its band structure shows that there are four edge states at k = 0.5, in which the three electrons distribute at three outside edge sites, and the last electron is shared equally(50%) by two sites near the central site. The lowest conductance step in the valley is 2, two times higher than that of monolayer ZGNR(M-ZGNR). Furthermore, in one quasithree-dimensional hexagonal lattice built, both of the Dirac points and the zero-energy states appear in the band structure along the z-axis for the fixed zero k-point in the x-y plane. In addition, it is an insulator in the x-y plane due to band gap 4 eV, however, for any k-point in the x-y plane the zero-energy states always exist at k_z = 0.5.     

Structural and electronic properties of a single C chain doped zigzag BN nanoribbons

The effects of single C-chain on the stability, structural and electronic properties of zigzag BN nanoribbons (ZBNNRs) were investigated by first-principles calculations. C-chain was expected to dope at B-edge for all the ribbon widths _Nz$N_z$ considered. The band gaps of C-chain doped _Nz$N_z$-ZBNNR are narrower than that of perfect ZBNNR due to new localized states induced by C-chain. The band gaps of _Nz$N_z$-ZBNNR-C(n  ) are direct except for the case of C-chain position n=2$n=2$. Band gaps of BN nanoribbons are tunable by C-chain and its position n, which may endow the potential applications of BNNR in electronics.     

Zigzag型边界石墨烯纳米带的电子态

在紧束缚近似下, 提出有限系统的Bloch定理方法, 解析计算了Zigzag型石墨烯纳米带的电子态和能带.研究发现, 其电子态有两类, 分别是驻波态和边缘态; 驻波态的波矢为实数, 波函数是正弦函数形式; 边缘态的波矢主要是虚数, 实数部分为零或者π/2, 波函数是双曲正弦函数形式. Zigzag型石墨烯纳米带的能带由驻波态能量和边缘态能量组成, 我们推导了边缘态的关于无限长方向波矢和能量的精确取值范围. 讨论了边缘态和驻波态的过渡点, 发现两种电子态通过不同的方式在受限波矢趋于零时关于格点位置逼近线性关系. 当受限方向也变成无限长时, 可以得到与无限大石墨烯相同的能带关系. 关键词： 紧束缚模型 Zigzag型石墨烯纳米带 边缘态     

Modulating magnetism of nitrogen-doped zigzag graphene nanoribbons

We present a study of electronic properties of zigzag graphene nanoribbons （ZGNRs） substitutionally doped with nitrogen atoms at a single edge by first principle calculations. We find that the two edge states near the Fermi level sepa- rate due to the asymmetric nitrogen-doping. The ground states of these systems become ferromagnetic because the local magnetic moments along the undoped edges remain and those along the doped edges are suppressed. By controlling the charge-doping level, the magnetic moments of the whole ribbons are modulated. Proper charge doping leads to interest- ing half-metallic and single-edge conducting ribbons which would be helpful for designing graphene-nanoribbon-based spintronic devices in the future.     

First principle study of edge topological defect-modulated electronic and magnetic properties in zigzag graphene nanoribbons

Zigzag graphene nanoribbon(ZGNR) is a promising candidate for next-generation spintronic devices. Development of the field requires potential systems with variable and adjustable electromagnetic properties. Here we show a detailed investigation of ZGNR decorated with edge topological defects(ED-ZGNR) synthesized in laboratory by Ruffieux in 2015[Pascal Ruffieux, Shiyong Wang, Bo Yang, et al. 2015 Nature 531 489]. The pristine ED-ZGNR in the ground state is an antiferromagnetic semiconductor, and the acquired band structure is significantly changed compared with that of perfect ZGNR. After doping heteroatoms on the edge, the breaking of degeneration of band structure makes the doped ribbon a half-semi-metal, and nonzero magnetic moments are induced. Our results indicate the tunable electronic and magnetic properties of ZGNR by deriving unique edge state from topological defect, which opens a new route to practical nano devices based on ZGNR.