嘧啶与苯环对分子器件伏一安特性影响的差异研究

利用从头计算方法和弹性散射格林函数理论,对四苯分子和二嘧啶二苯分子电输运性质进行理论研究.结果显示,四苯分子比二嘧啶二苯分子具有更好的电输运能力,二嘧啶二苯分子显示出较好的整流特性.四苯分子较好的电输运性能力源于其部分分子轨道同时与两电极均有较好耦合,而二嘧啶二苯分子中,由于结构的不对称,使得对导电起主要贡献的分子轨道都局域于体系的一端.     

嘧啶与苯环对分子器件伏—安特性影响的差异研究

利用从头计算方法和弹性散射格林函数理论,对四苯分子和二嘧啶二苯分子电输运性质进行理论研究。结果显示,四苯分子比二嘧啶二苯分子具有更好的电输运能力,二嘧啶二苯分子显示出较好的整流特性。四苯分子较好的电输运性能源于其部分分子轨道同时与两电极均有较好耦合,而二嘧啶二苯中,由于结构的不对称,使得对导电起主要贡献的分子轨道都局域于体系的一端。     

自旋轨道耦合Su-Schrieffer-Heeger原子链系统的电子输运特性

在Su-Schrieffer-Heeger (SSH)原子链中,电子在胞内和胞间的跳跃依赖于其自旋时,即SSH原子链存在自旋轨道耦合作用时,存在不同缠绕数的非平庸拓扑边缘态.如何探测自旋轨道耦合SSH原子链不同缠绕数的边缘态是一个重要问题.本文在紧束缚近似下研究了自旋轨道耦合SSH原子链的非平庸拓扑边缘态性质及其零能附近的电子输运特性.研究发现四重和二重简并边缘态的缠绕数分别为2和1;并且仅当源极入射电子的自旋被极化(铁磁电极)时,自旋轨道耦合SSH原子链在零能附近的电子输运特性才能反映其边缘态的能谱特性.尤其是,随着自旋轨道耦合SSH原子链与左、右导线之间的耦合强度由弱到强改变,对于缠绕数为2的四重简并边缘态,入射电子在零能附近的透射峰数目将从4个变为0;而对于缠绕数为1的二重简并边缘态情形,其透射峰数目将从2个变为0.因此,在源极为铁磁电极的情形下,通过观察自旋轨道耦合SSH原子链在零能附近电子共振透射峰的数目随着其与左、右导线之间耦合强度的变化,来探测其不同缠绕数的边缘态.上述结果为基于电子输运特性探测自旋轨道耦合SSH原子链不同拓扑性质的边缘态提供了一种可选择的理论方案.     

六元杂环分子电学特性的理论研究

在第一性原理基础上，利用弹性散射格林函数方法，研究了六元杂环分子结2,5-哒嗪二硫酚 、2,5-吡嗪二硫酚和2,5-嘧啶二硫酚的电子输运特性，分析了终端原子的选取对杂环分子吡 啶电学特性的影响. 利用分子前线轨道理论和微扰方法定量地确定了分子与金属的相互作用 能参数. 计算结果表明，2,5-哒嗪二硫酚具有较好的电学特性，而2,5-嘧啶二硫酚在外加电 压较低时电导值比较小. 对于吡啶分子，选取硒原子作为终端原子时，其导电特性优于分别 以氧原子和硫原子作为终端原子的情况. 关键词： 六元杂环分子 伏安特性 电子输运 分子电子学     

分子结点电子输运性质的理论研究

采用基于密度泛函理论的非平衡态格林函数方法,研究了Pt-H₂微结点在平衡态和低偏压下的电子输运行为,考察了电极-分子耦合形貌对结点输运性质的影响,并采用费曼路径概念从结点局域轨道出发分析了其输运特性. 发现H₂分子的反键轨道可以参与结点的低偏压电子输运,偏压可以通过改变系统局域分子轨道来影响其输运性质. 关键词： 分子结点 电子输运 非平衡态格林函数方法 透射谱     

接触构型及电极距离对4,4’-二巯基二苯醚分子电输运性质的影响

利用从头计算方法和弹性散射格林函数的方法,对4,4'-二巯基二苯醚分子电输运特性的研究结果显示,分子与电极之间接触点的构型以及两电极之间的距离对4,4'-二巯基二苯醚分子的电输运性质都有很大影响.电流随电极距离的变化与耦合系数的变化存在着密切关系.分子末端硫原子处于金原子的顶位上时电流的开启电压很小,而处在金(111)面的空位上时约有1.0V左右电流禁区.与实验结果相比,硫原子更可能处在金(111)面的空位上方.     

分子和金表面相互作用的第一性原理研究

硫氢官能团可以很强地吸附于金表面上,从而可作为连接体用于纳米电子学中的分子器件.从第一性原理出发利用密度泛函理论研究了4,4′二巯基联苯分子和金表面的相互作用,并利用了前线轨道理论和微扰理论定量地确定了该相互作用能常数.计算结果表明,当含有硫氢官能团的有机分子化学吸附于金表面时,硫原子将与金原子形成以共价键为主的混和键,此时一些分子轨道扩展于金原子和有机分子中,这些轨道为分子结中电子的输运提供了通道,从而可使分子线的电导呈现出欧姆特性.而其他分子轨道具有局域性,此时电子的输运只能通过隧道效应来实现. 关键词： 化学吸附 分子线 分子电子学     

分子的位置取向对分子器件电输运特性的影响

以1,4-二硫酚(DTB)分子为研究对象，利用第一性原理计算方法和非平衡格林函数理论，研究了分子的位置取向对分子电子结构以及分子结电输运性质的影响.计算结果表明，分子位置取向的改变会影响分子的电子结构，从而影响分子体系的电输运特性，扩展分子的平衡态不是电子输运的最佳状态，适当调节分子的位置取向可以提高分子的电输运特性. 关键词： 位置取向 电子输运 分子电子学     

门电场对有机单分子器件的影响 (cited: 3)

基于第一性原理和弹性散射格林函数方法,从理论上研究了门电场对一系列有机单分子结的电输运性质的影响. 结果显示,含有氧化还原中心并且在门电场方向具有较大电偶极矩的分子结能够对门电场有显著响应. 2,5-二甲基噻吩二硫醇的伏安特性显示了类似N-沟道金属氧化物半导体管性质. 这一独特的伏安特性可以从能级、耦合能以及原子电荷随门电场的演化来理解.     

电极位置和截面尺寸对分子器件输运性质的调控

研究表明分子器件的性能受器件结构搭建精度影响,分子与电极接触构型的微弱变化可能引起电输运特性较大差异.本文运用密度泛函理论和非平衡格林函数相结合的方法,研究了由金纳米线与benzene-1,4-dithiol（BDT）形成的分子结的电输运性质.通过对不同的Au-BDT接触构型输运性质的研究,发现当两电极处于对位构型时,有较好的电荷输运行为,而且比较符合制备工艺要求;当电极偏离轴线的角度不大于5°,且电极散射截面尺寸不小于4×4时,该分子结体系的电导和透射谱均比较稳定.电极截面尺寸小于4×4或者电极偏离轴线的夹角大于5°时,透射谱在费米能级附近出现不连续现象,导致体系电导降低.较小电极截面尺寸或者电极以较大角度偏离轴线将导致该分子结体系电导降低和透射谱连续性降低,主要是组成电极的金原子轨道与苯基分子轨道耦合缺失造成的.该研究为Au-BDT-Au体系设计和制备过程中电极的位置及电极截面尺寸做了科学的界定.     

First-principle studies of I-V properties of a molecular wire

The elastic scattering Green function method has been developed to describe the I-V characteristics of molecular wires. The molecular electronic structure and the interaction between the molecule and the gold surface are two key factors for the charge transport properties of molecular wires in the formulas. An ab initio calculation at the hybrid density functional theory level is carried out to obtain the electronic structure of 4-4′-dimercaptodibenzene molecule. The frontier orbit theory and the perturbation theory are employed to determine the constant of the interaction energy between molecule and surface quantitatively. The numerical results show that the bonding between the sulfur atom and the gold atoms corresponds mainly to the covalent bond. Some molecular orbits are extended over molecule and gold cluster that certainly give channels for the charge transport, other molecular orbits are localized and the charge transport can take place by tunnel mechanism. At zero bias region, there exists a current gap. With the increasing bias, the conductance of the wire takes a shape of plateaus.     

First-principle studies of I–V properties of a molecular wire

The elastic scattering Green function method has been developed to describe the I–V characteristics of molecular wires. The molecular electronic structure and the interaction between the molecule and the gold surface are two key factors for the charge transport properties of molecular wires in the formulas. Anab initio calculation at the hybrid density functional theory level is carried out to obtain the electronic structure of 4-4′-dimercaptodibenzene molecule. The frontier orbit theory and the perturbation theory are employed to determine the constant of the interaction energy between molecule and surface quantitatively. The numerical results show that the bonding between the sulfur atom and the gold atoms corresponds mainly to the covalent bond. Some molecular orbits are extended over molecule and gold cluster that certainly give channels for the charge transport, other molecular orbits are localized and the charge transport can take place by tunnel mechanism. At zero bias region, there exists a current gap. With the increasing bias, the conductance of the wire takes a shape of plateaus.     

1,8-二巯基芘分子电学特性的理论研究

在第一性原理的基础上 ,对 1,8 二巯基芘分子的电学特性进行了理论研究 .采用了 3个Au原子构成的团簇来模拟Au表面 .首先利用密度泛函理论计算了 1,8 二巯基芘分子的电子结构及其和Au表面的相互作用 ,再利用前线轨道理论和微扰理论定量地确定了该分子和Au表面的相互作用能常数 .最后利用弹性散射格林函数法研究了该分子结的伏 安特性 .计算结果表明 ,分子中的硫原子和Au原子形成很强的共价键 .当外加偏压小于 1V时分子结存在电流禁区 ,随着偏压升高 ,分子结的电导出现平台结构 .分子结的电导特性和其电子结构密切相关 ,扩展分子轨道为电荷的迁移提供了通道 ,而局域轨道对电流贡献很小     

Effect of crystallographic orientations on transport properties of methylthiol-terminated permethyloligosilane molecular junction

The understanding of the influence of electrode characteristics on charge transport is essential in the field of molecular electronics. In this work, we investigate the electronic transport properties of molecular junctions comprising methylthiol-terminated permethyloligosilanes and face-centered crystal Au/Ag electrodes with crystallographic orientations of (111) and (100), based on the ab initio quantum transport simulations. The calculations reveal that the molecular junction conductance is dominated by the electronic coupling between two interfacial metal-S bonding states, which can be tuned by varying the molecular length, metal material of the electrodes, and crystallographic orientation. As the permethyloligosilane backbone elongates, although the σ conjugation increases, the decreasing of coupling induced by the increasing number of central Si atoms reduces the junction conductance. The molecular junction conductance of methylthiol-terminated permethyloligosilanes with Au electrodes is higher than that with Ag electrodes with a crystallographic orientation of (111). However, the conductance trend is reversed when the electrode crystallographic orientation varies from (111) to (100), which can be ascribed to the reversal of interfacial coupling between two metal-S interfacial states. These findings are conducive to elucidating the mechanism of molecular junctions and improving the transport properties of molecular devices by adjusting the electrode characteristics.     

分子结电学特性的理论研究

在第一性原理的基础上，对共扼分子2-氨基-5-硝基-1，4-二乙炔基-4’，-苯硫醇基苯(2-amino-5-nitro-1,4-diethyny-4’-benzenethiol-benzene)与金表面形成的分子结的电学特性进行了理论研究.利用密度泛函理论计算了该分子及扩展分子的电子结构；讨论了分子与金表面的相互作用，定量地确定了耦合常数，求出了电子的迁移强度；利用弹性散射格林函数法研究了该分子结的伏—安特性.计算结果表明，当外加偏压小于0.9V时分子结存在电流禁区，随着偏压升高，分子结的电导出现平台特 关键词： 化学吸附 分子结 分子电子学     

Electronic properties of single-molecule junction: Effect of the molecular distortion

For a model system consisting of a benzenedithio (BDT) molecule sandwiched between two Au plates, the electronic properties as a function of different BDT geometry are investigated using density functional theory. The distorted BDT structures are got through stretching the electrode distance. The corresponding electronic properties, including the spatial distribution of the frontier orbits, the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital levels and density of states at the Fermi energy are determined. It reveals that the molecular distortion essentially determines electronic structures. The result should be beneficial to understand the stress-dependent or structure-dependent transport mechanism of electrons of the BDT junction.     

Hydration effect on the electronic transport properties of oligomeric phenylene ethynylene molecular junctions

A first-principles computational method based on the hybrid density functional theory is developed to simulate the electronic transport properties of oligomeric phenylene ethynylene molecular junctions with H₂O molecules accumulated in the vicinity as recently reported by Na {\it et al.} [\wx{Nanotechnology}{18} 424001 (2007)]. The numerical results show that the hydrogen bonds between the oxygen atoms of the oligomeric phenylene ethynylene molecule and H₂O molecules result in the localisation of the molecular orbitals and lead to the lower transition peaks. The H₂O molecular chains accumulated in the vicinity of the molecular junction can not only change the electronic structure of the molecular junctions, but also open additional electronic transport pathways. The obvious influence of H₂O molecules on the electronic structure of the molecular junction and its electronic transport properties is thus demonstrated.     

分子线电子输运特性的第一性原理研究

从第一性原理出发 ,利用密度泛函理论研究了SH -C8H16-SH分子和金表面的相互作用 ,并利用分子前线轨道理论和微扰理论定量地确定了该相互作用能常数 ,然后 ,利用弹性散射格林函数方法研究了该分子与金表面形成的分子线的伏 安特性 .研究结果表明 ,当含有硫氢官能团的有机分子化学吸附于金表面时 ,硫原子将与金原子形成以共价键为主的混和键 ,此时 ,扩展的分子轨道使分子线的电导呈现出欧姆特性 ,而对于局域的分子轨道 ,电子的输运只能通过隧道效应来实现 .对分子线伏 安特性的计算结果显示 ,在零偏压附近 ,存在一个电流禁区 ,随着偏压的增加 ,分子线的电导呈现出平台特征 .     

Transmission characteristics including the coupling effect between normal and lateral degrees of freedom in step-barrier structures with a longitudinal magnetic field

In this paper we study the tunneling transport phenomena in a step-barrier structure under the influence of a longitudinal magnetic field, where the magneto-coupling effect is taken into account between the longitudinal motion component and the transverse Landau orbits of an electron. We also present numerical results of single square-barrier and asymmetrical double-barrier heterostructures for comparison. The results show that the coupling effect can play important role during the electronic tunneling process. It not only causes a significant shift of resonant peaks toward the low-energy region, but also enhances the transmission probability.