联苯二胺分子器件电输运特性的取代效应

在第一性原理基础上,理论研究了苯环上含有不同取代物的四个联苯分子的电输运特性。计算结果表明，当苯环上的氢被取代时，联苯分子的两个苯环之间的扭转角增大。分子结的电导随苯环间扭转角的增加而减少,且电导值与扭转角余弦平方成线性关系。在低偏压下，分子结的电输运机制是电子通过 轨道的隧穿过程。计算结果与实验结果符合的较好。     

分子构型对分子器件伏-安特性的影响

本文选取4,4′-二巯基联苯分子通过终端S原子化学吸附于两Au原子团簇形成分子结,利用从头计算方法和弹性散射格林函数理论研究了该分子两苯环之间不同位置取向对分子能级结构以及该分子结伏安特性的影响.计算结果表明苯环扭转角增加会使分子能级发生不同程度的移动,从而引起最高占据轨道(HOMO)与最低未占据轨道(LUMO)的间距增大.扭转角增大也会导致分子轨道的扩展性变差,从而使体系的导电性能降低.当扭转角为90度时,体系的导电性能最差.该工作有利于未来分子电子学器件的设计.     

分子构型对分子器件伏-安特性的影响

本文以4,4'-二巯基联苯分子为研究对象,利用从头计算方法和弹性散射格林函数理论,研究了苯环之间的不同位置取向对分子的电子结构以及该分子结的伏安特性的影响.计算结果表明苯环扭转角不同会改变分子的电子结构,扭转角的增大会导致分子轨道的扩展性变差,从而使体系的导电性能降低.     

分子构型对分子器件伏-安特性的影响

本文以4，4’-二巯基联苯分子为研究对象，利用从头计算方法和弹性散射格林函数理论，研究了苯环之间的不同位置取向对分子的电子结构以度该分子结的伏安特性的影响．计算结果表明苯环扭转角不同会改变分子的电子结构。扭转角的增大会导致分子轨道的扩展性变差，从而使体系的导电性能降低．     

官能团对芳烃体系电学特性的影响

以联苯分子为研究对象,利用密度泛函理论和弹性散射格林函数方法,研究了不同官能团对分子的电子结构以及分子结电输运性质的影响.计算结果表明在分子中的同一位置添加不同的官能团时,会使分子的几何结构和电子结构发生变化,从而影响分子结的电输运性质.     

官能团对芳烃体系电学特性的影响

以联苯分子为研究对象,利用密度泛函理论和弹性散射格林函数方法,研究了不同官能团对分子的电子结构以及分子结电输运性质的影响.计算结果表明在分子中的同一位置添加不同的官能团时,会使分子的几何结构和电子结构发生变化,从而影响分子结的电输运性质.     

电极距离对分子器件电输运特性的影响

以4,4′_二巯基联苯分子为研究对象，利用从头计算方法和弹性散射格林函数理论，研究了两个电极之间的距离对分子几何结构和电子结构以及该分子结电输运性质的影响. 计算结果表明，电极距离的不同会改变分子的几何结构和电子结构，从而影响分子体系的电输运特性. 扩展分子的平衡状态不是电子输运的最佳状态，适当调整两个电极之间距离可以改善分子的电输运特性. 关键词： 电极距离 伏 安特性 分子电子学     

官能团对分子器件电输运特性的影响

以4,4′-二巯基联苯分子为研究对象,利用第一性原理计算方法和非平衡格林函数理论,研究了官能团氨基和硝基对分子的电子结构以及分子结电输运性质的影响. 计算结果表明,在分子的不同位置添加同一类官能团氨基会使分子的电子结构发生变化,从而影响分子结的电输运性质. 而在分子的同一位置添加不同类型的官能团氨基和硝基则对分子间的相互作用有着显著影响,会使分子发生转动,从而改变分子的几何结构和电子结构,影响分子结的电输运特性. 并且发现随着分子的转动,添加官能团硝基时分子会呈现出记忆功能. 关键词： 官能团 电子输运 分子电子学     

4 ,4′-二巯基二苯醚分子的电子输运性质研究

利用从头算方法和弹性散射格林函数理论,研究了4 ,4′-二巯基二苯醚分子的电输运性质.计算表明,当外加偏压少于0 .9 V时,该分子器件不导电.当外加偏压进一步增加时,该分子器件的电导呈现出平台特征.由于中间氧原子的存在,相对于4 ,4′-二巯基联苯分子来说,该分子的导电特性较差.     

有机分子结构对其电输运性质的影响

利用从头算理论和弹性散射格林甬数的方法,对有机分子1,4.苯二硫酚(benzene-1,4-dithiol)、4,4二巯基联苯(4,4-biphenyldithiol)、4,4:二巯基联苯醚(bis-(4-mercaptonphenyl)-ether)以及对苯二甲氰(1,4-phenylene diisocy-anide)的电子输运性质进行了理论研究和比较分析.结果显示前三种巯基分子在开启电压位置、电导的平台效应和电流的线性响应等方面有相似性,其中1,4-苯二硫酚分子的电输运性能优越于其他两个分子,但氰基分子对苯二甲氰却有较明显的区别.     

Thermopower and conductance for a graphene p-n junction

The thermopower and conductance in a zigzag graphene p-n junction are studied by using the nonequilibrium Green's function method combined with the tight-binding Hamiltonian. Our results show that the conductance and thermopower of the junction can be modulated by its width, the potential drop, and the applied perpendicular magnetic fields. A narrow graphene p-n junction shows insulating characteristics, and its thermopower is much larger than that of the wider one around the Dirac point. The insulating characteristic of the junction decreases as the width increases. In particular, with increasing junction width or the potential drop, the first conductance plateau is strongly enhanced and the thermopower is inverted around the Dirac point. A perpendicular magnetic field strongly suppresses the conductance and enhances the thermopower in the p-n region. The influence of edge vacancy defects on the conductance and thermopower is also discussed. Our results provide theoretical references for modulating the electronic and thermal properties of a graphene p-n junction by tuning its geometry and working conditions.     

自旋轨道耦合作用下石墨烯pn结的电子输运性质

本文研究了自旋轨道耦合作用下石墨烯纳米带pn结的电子输运性质. 当粒子的入射能量处于pn结两端势能之间时, 粒子将会以隧穿的形式通过石墨烯pn结, 同时伴随着电子空穴转换. 电导随费米能的变化曲线呈不等高阶梯状, 并在费米能位于pn结两端能量中点时取得最大值. 随着石墨烯pn结长度的增加, 电导以指数形式衰减. 自旋轨道耦合作用导致的能隙会使电导显著减小, 而边缘态的粒子则可以几乎毫无阻碍地通过pn结. 本文用一个简单的子带隧穿模型解释了上述特征. 最后还研究了在pn转换区中掺入替位杂质的情况. 在弱杂质下, 电导随费米能变化的曲线将不再对称; 当杂质较强时, 仅边界态的形成的电导台阶能够保持.     

Voltage-dependent conductance states of a single-molecule junction

Ag-Sn-phthalocyanine-Ag junctions are shown to exhibit three conductance states. While the junctions are conductive at low bias, their impedance drastically increases above a critical bias. Two-level fluctuations occur at intermediate bias. These characteristics may be used to protect a nanoscale circuit. Further experiments along with calculations reveal that the self-limiting conductance of the junctions is due to reversible changes of the junction geometry.     

Electron transport in manganite bicrystal junctions

The transport and magnetic properties of junctions created in La_0.67Sr_0.33MnO₃ thin films epitaxially grown on substrates with a bicrystal boundary have been investigated. In tilted neodymium gallate bicrystal substrates, the NdGaO₃(110) planes are inclined at angles of 12° and 38°. The temperature dependences of the electrical resistance, magnetoresistance, and differential conductance of the junctions at different voltages have been measured and analyzed. It has been found that the magnetoresistance and electrical resistance of the junction significantly increase with an increase in the misorientation angle, even though the misorientation of the easy magnetization axes remains nearly unchanged. The ratio of the spin-dependent and spin-independent contributions to the conductance of the bicrystal junction increases by almost an order of magnitude with an increase in the misorientation angle from 12° to 38°. The magnetoresistance of the junction increases with decreasing temperature, which is most likely associated with an increase of the magnetic polarization of the electrons. It has been shown that, at low (liquid-helium) temperatures, the conductance depends on the voltage V according to the law V ^1/2, which indicates the dominant contribution from the electron-electron interaction to the electrical resistance of the junction. An increase in the temperature leads to a decrease in this contribution and an increase in the contribution proportional to V ^3/2, which is characteristic of the mechanism involving inelastic spin scattering by surface antiferromagnetic magnons.     

Shot Noise in Ferromagnetic Superconductor Tunnel Junctions

In this paper, the superconducting order parameter and the energy spectrum of the Bogoliubov excitations are obtained from the Bogoliubov-de Gennes (BdG) equation for a ferromagnetic superconductor (FS). Taking into account the rough interface scattering effect, we calculate the shot noise and the differential conductance of the normal-metal insulator ferromagnetic superconductor junction. It is shown that the exchange energy E_h in FS can lead to splitting of the differential shot noise peaks and the conductance peaks. The energy difference between the two splitting peaks is equal to 2E_h. The rough interface scattering strength results in descent of conductance peaks and the shot noise-to-current ratio but increases the shot noise.     

Gas-sensor property of single-molecule device:F_2 adsorbing effect

The single thiolated arylethynylene molecule with 9,10-dihydroanthracene core(denoted as TADHA) possesses pronounced negative differential conductance(NDC) behavior at lower bias regime. The adsorption effects of F_2 molecule on the current and NDC behavior of TADHA molecular junctions are studied by applying non-equilibrium Green's formalism combined with density functional theory. The numerical results show that the F_2 molecule adsorbed on the benzene ring of TADHA molecule near the electrode can dramatically suppresses the current of TADHA molecular junction. When the F_2 molecule adsorbed on the conjugated segment of 9,10-dihydroanthracene core of TADHA molecule, an obviously asymmetric effect on the current curves induces the molecular system showing apparent rectifier behavior. However, the current especially the NDC behavior have been significantly enlarged when F_2 addition reacted with triple bond of TADHA molecule.     

量子线/铁基超导隧道结中隧道谱的研究

考虑铁基超导中能带间的相互作用和界面对每一个能带的散射作用, 利用推广的Blonder-Tinkham-Klapwijk模型, 并通过求解Bogoliubov-de Gennes 方程研究了具有不同类型双能隙系统的量子线/铁基超导隧道结中准粒子的输运系数和隧道谱. 研究表明: 1)在弹道极限时, 随着带间相互作用的增大, s_± 波隧道谱中零偏压附近的平台演变成电导峰; s₊₊ 波的平台演变成凹陷; p波的零偏压电导峰被压低. 2)界面对两个能带的散射作用不为零时, 随着带间相互作用的增大, s_± 波和s₊₊ 波两能隙处的峰值将降低, 而两峰间的凹陷值将变大; p波的零偏压电导峰被压低, 非零偏压电导增大. 3)界面对每个能带的散射, 可使其产生的电导峰变得更加尖锐, 但可压低和抹平另一个带产生的电导峰值. 这些结果对于澄清铁基超导体的能隙结构和区别不同类型铁基超导体有所帮助.     

Spin-polarized quasiparticle transport in ferromagnet/d-wave superconductor junctions

Within a scattering framework, a theoretical study is presented for the spin-polarized quasiparticle transport in ferromagnet/d-wave superconductor junctions. We find that the subgap conductance behavior is qualitatively different from a nonmagnetic junction, and can also be significantly different from those of a ferromagnet/s-wave junction. For a ballistic ferromagnet/d-wave superconductor junction, under appropriate conditions, a zero-bias conductance minimum could be achieved. In addition, a conductance maximum at finite bias could be evolved by interfacial scattering. For a normal-metal/ferromagnet/d-wave superconductor junction, conductance resonances are predicted.     

Disorder-induced enhancement of transport through graphene p-n junctions

We investigate the electron transport through a graphene p-n junction under a perpendicular magnetic field. By using the Landauer-Büttiker formalism combined with the nonequilibrium Green function method, the conductance is studied for clean and disordered samples. For the clean p-n junction, the conductance is quite small. In the presence of disorders, it is strongly enhanced and exhibits a plateau structure at a suitable range of disorders. Our numerical results show that the lowest plateau can survive for a very broad range of disorder strength, but the existence of high plateaus depends on system parameters and sometimes cannot be formed at all. When the disorder is slightly outside of this disorder range, some conductance plateaus can still emerge with its value lower than the ideal value. These results are in excellent agreement with a recent experiment.