金属/掺杂聚合物/金属结构中载流子的注入与输运

基于紧束缚的Su-Schrieffer-Heeger模型,利用非绝热的动力学方法,研究了金属/聚合物/金属三明治结构中载流子注入与输运的动力学过程,其中,聚合物中含有一个掺杂离子. 电子波函数随时间的演化满足含时Schrdinger方程,晶格运动满足经典的牛顿运动方程. 研究发现,掺杂离子对注入到聚合物中的载流子的作用类似一个控制阀门,阀门的状态与电场的强度和偏压的大小密切相关. 关键词： 载流子输运 波包 非绝热动力学     

载流子在金属/聚对苯乙炔/金属结构中注入及输运的动力学研究

采用紧束缚的Su-Schrieffer-Heeger模型,利用非绝热动力学方法研究了载流子在金属/聚对苯乙炔(poly(p-phenylene vinylene,简记为PPV))/金属三明治结构中注入与输运的动力学过程.发现由于强的电子-晶格相互作用,注入的电荷在PPV链中形成波包,波包的形成与施加在金属电极上的偏压、PPV链上的电场强度及金属电极与PPV之间的界面耦合强度密切相关.在无外电场的情况下,当偏压达到临界值时电荷能够从金属电极注入到PPV链中并形成波包.随着电场强度的增大,波包能 关键词： 金属/聚对苯乙炔/金属结构 载流子输运 波包     

Ir(PPY)3掺杂PVK的电致发光机理

近几年来发展起来的电致磷光(electrophosphorescence)是有机发光二极管(OLED)研究的新生长点。对电致磷光发光机理的研究随即得到了人们普遍的关注。比较了不同正向偏压条件下Ir(PPY)₃掺杂聚乙烯基咔唑(PVK)的光致发光(PL)和电致发光(EL)光谱。研究结果显示在电场和注入电流的共同作用下,PL光谱中基质PVK发光的相对强度并没有发生显著的变化。电场或注入载流子不会影响PVK向Ir(PPY)₃的能量传递。磷光掺杂聚合物EL主要是由于载流子在掺杂磷光分子上的直接复合,而不是由基质向磷光掺杂分子的能量传递。     

物理型硬件木马失效机理及检测方法

对两种物理型硬件木马造成芯片退化或失效的机理进行了详细分析. 通过使用ATLAS 二维器件仿真系统并结合SmartSpice电路逻辑仿真器, 模拟了两种物理型硬件木马对反相器逻辑电路输出特性的影响. 使用ATHENA工艺仿真系统模拟了掺杂离子注入工艺过程, 实现了掺杂型硬件木马的金属-氧化物-半导体场效应管(MOSFET)器件; 使用热载流子注入退化模型对ATLAS 仿真器件进行热载流子压力测试, 以模拟热载流子注入型硬件木马注入MOSFET器件并造成器件退化失效的过程, 分别将上述掺杂型硬件木马和热载流子注入型硬件木马的MOSFET器件与另一个正常MOSFET器件组成同样的反相器逻辑电路. 反相器使用Spice 逻辑电路仿真输出DC直流、AC瞬态传输特性以研究物理型硬件木马对电路输出特性的影响. 为了研究MOSFET器件的物理特性本身对硬件木马的影响, 在不同温度不同宽长比(W/L)下同样对反相器进行Spice电路逻辑输出仿真. 本文分析了离子掺杂工艺、热载流子注入压力测试形成的物理型硬件木马随压力强度、温度的变化对逻辑电路输出特性的影响. 通过结果对比分析得出了含有物理型硬件木马的逻辑电路在DC直流输出特性上的扰动比AC瞬态传输特性更明显的结论. 因此, 本文提出了一种针对物理型硬件木马的检测流程. 同时, 该检测流程是一种具有可操作性的检测物理型硬件木马的方法.     

聚合物纳米复合电解质(PEO)8-ZnO-LiClO4微结构及电导率研究

以聚氧化乙烯(PEO)为基质,成功制备出纳米ZnO掺杂的(PEO)₈-ZnO-LiClO₄离子导电聚合物电解质,并利用多种实验技术,包括扫描电子显微镜、X射线衍射(XRD)、傅里叶变换红外光谱和正电子湮没寿命谱(PALS),系统地研究了纳米ZnO与基质间相互作用及其对聚合物链段运动、纳米尺度自由体积、离子输运和复合电解质电导率的影响.实验结果发现,纳米ZnO的掺杂使聚合物电解质的离子电导率得到了大幅度提高,当ZnO与PEO质量比为6%时达到最大,(PEO)₈-ZnO-LiClO₄的电导率为1.82×10^-4 S ·cm^-1,比(PEO)₈-LiClO₄的电导率(6.58×10^-5 S ·cm^-1)提高了大约一个数量级.XRD结果显示,纳米ZnO的加入降低了PEO的结晶性,增加了锂离子传输的非晶相,从而提高了电导率.离散PALS测量结果表明,随着纳米ZnO的加入,复合电解质的自由体积、浓度和相对自由体积分数f_r均增加.连续PALS分析揭示了自由体积的分布由一个峰劈裂成两个峰,表明纳米ZnO的掺杂对聚合物的微结构有很大影响.基于实验测量的f_r和离子电导率,研究了离子导电机理.研究发现, f_r与电导率之间存在一个直接关系,即f_r越大,越有利于锂离子的传输,导致电导率越大.这个结果支持聚合物电解质导电的自由体积理论. 关键词： 正电子湮没寿命谱 聚合物纳米复合电解质 离子电导率 自由体积     

肖特基势垒对铁磁/有机半导体结构自旋注入性质的影响

理论研究了铁磁/有机半导体肖特基接触时的电流自旋极化注入,并讨论了电流自旋极化率随界面处肖特基势垒高度、有机半导体层中特殊载流子及其迁移率、界面附近掺杂浓度的变化关系.通过计算发现,寻找在势垒区中载流子迁移率比较大的有机半导体材料对实现有效的自旋注入是必要的;同时还发现,由于铁磁/有机半导体接触而形成的肖特基势垒不利于自旋注入.因此要想实现有效的自旋注入,界面附近必须采用重掺杂来有效减少势垒区的宽度,且势垒的高度要限制在一定的范围内.     

理论计算中电势能零点的选取对电荷注入的影响

基于紧束缚的Su-Schrieffer-Heeger(SSH)模型,利用非绝热的动力学方法,研究了金属/聚合物结构中电势能零点的选取对电荷注入的影响.理论计算发现,电场越强,电势能零点的选取对电荷注入的影响就越大. 关键词： 电势能 电荷注入 非绝热动力学     

氧含量对Fe掺杂YBCO体系中载流子局域化与离子团簇效应的影响

对YBa₂Cu_3-xFe_xO_y（x=00，01，02 ）和YBa₂Cu_2.8Fe_0.2O_y（y=705—653 ）系列样品的氧含量、霍尔系数和超导电性进 行了系统的研究.结果表明，氧含量的变化对样品中载流子的输运和转移及超导电性有重要 影响；适当增加氧含量可以减缓Cu(1)位元素替代对超导转变温度T_c的抑制；在 CuO₂面上参与输运的载流子（空穴）浓度是影响样品超导电性的关键因素.从电 荷转移模型出发 ，结合掺杂离子引起的载流子局域化和离子团簇效应，对载流子浓度随掺杂量和氧含量的变 化从微观结构方面进行了讨论.元素替代量的增加或者氧含量的降低（相同替代量的情况下 ）都将导致Cu-O链区的有效氧空位增多，导致替代元素的离子团簇效应和载流子局域化效应 趋于增强，这是引起参与输运的载流子浓度下降，进而导致T_c降低的主要原因. 关键词： 氧含量 霍尔系数 载流子局域化 离子团簇效应     

铁磁/有机半导体/铁磁系统的电流自旋极化性质研究

根据有机半导体中的电流自旋极化注入和输运实验现象，理论上研究了铁磁/有机半导体/铁磁系统的电流自旋极化性质.考虑到有机半导体的具体特性，从自旋扩散理论和欧姆定律出发，得到了系统的电流自旋极化率.假设自旋极化子和不带自旋的双极化子为有机半导体中的载流子.通过计算发现，极化子为实现有机半导体中电流极化注入和输运的有效自旋载流子，即使它只占总载流子很少一部分.还进一步研究了自旋相关界面电阻和电导率匹配以及有机半导体长度等因素对系统电流自旋极化的影响. 关键词： 自旋电子学 自旋注入 有机半导体 极化子     

基态非简并聚合物中的极化子和双极化子动力学

研究了极化子和双极化子在基态非简并聚合物中的动力学.弱电场下，发现载流子为带电极 化子或双极化子，它们的晶格态与电荷态始终耦合在一起同步运动.极化子比双极化子的运 动速度快，存在饱和速度，且它们的饱和速度随聚合物非简并度的增加而降低；强电场下， 元激发的电荷态将脱离晶格态的束缚而快速运动，参与导电的不再是极化子或双极化子，而 是电子直接导电. 关键词： 极化子 双极化子 动力学模拟     

Thermoelectric-transport in metal/graphene/metal hetero-structure

We investigate the thermoelectric-transport properties of metal/graphene/metal hetero-structure. We use a single band tight-binding model to present the two-dimensional electronic band structure of graphene. Using the Landauer--Butticker formula and taking the coupling between graphene and the two electrodes into account, we can calculate the thermoelectric potential and current versus temperature. It is found that in spite of metal electrodes, the carrier type of graphene determines the electron motion direction driven by the difference in temperature between the two electrodes, while for n type graphene, the electrons move along the thermal gradient, and for p type graphene, the electrons move against the thermal gradient.     

超导体/正常金属/半导体/正常金属/超导体结的研究

在约瑟夫逊效应的理论研究中,大体上有微观和宏观两种方法。采用的是宏观的方法。利用推广的Ja-cobson方法,讨论了超导体/正常金属/半导体/正常金属/超导体结的约瑟夫逊效应,并在小电流假设下,推导出了该结的电流密度与位相之间的关系。     

Step voltage in metal/polyimide/organic molecule/polyimide/metal junction

A step structure, very similar to a Coulomb staircase, has been successfully observed in the current–voltage (I–V) characteristic of metal/polyimide (PI)/rhodamine-dendorimer (Rh-G2)/PI/metal junctions prepared by the Langmuir–Blodgett technique. Assuming Rh-G2 molecule functions like a metallic sphere and PI works as tunneling barriers, the I–V characteristic of the junctions was analyzed based on Coulomb blockade theory. Taking into account the presence of space charge at the PI-metal interface, which has been revealed by the surface potential measurement, the equation of threshold voltage of the step structure is derived. It was found that the derived equation is satisfactory to explain the I–V characteristic.     

金属/C2H2/金属结构中的电子输运

在紧束缚近似下,利用转移矩阵法对“金属/C2H2/金属”结构的分子导线的电子输运性质进行了研究。通过转移矩阵法求出转移矩阵和散射矩阵,从而解析地得到体系的透射系数和态密度的变化,并详细分析了透射系数对C2H2与金属的耦合强度及两个(CH)间的耦合强度的依赖关系。我们的结果显示这种结构的分子导线有着较好的开关特性。     

Formation dynamics of bipolaron in a metal/polymer/metal structure

Charge injection process from metal electrode to a nondegenerate polymer in a metal/ polymer/ metal structure has been investigated by using a nonadiabatic dynamic method. We demonstrate that the dynamical formation of a bipolaron sensitively depends on the strength of applied electric field, the work function of metal electrode, and the contact between the polymer and the electrode. For a given bias applied to one of the electrode (V₀) and coupling between the electrode and the polymer (t^′), such as V₀=0.79 eV and t^′=1 eV, the charge injection process depending on the electric field can be divided into the following three cases: (1) in the absence of the electric field, only one electron tunnels into the polymer to form a polaron near the middle of the polymer chain; (2) at low electric fields, two electrons transfer into the polymer chain to form a bipolaron; (3) at higher electric fields, bipolaron can not be formed in the polymer chain, electrons are transferred from the left electrode to right electrode through the polymer one by one accompanying with small irregular lattice deformations.     

Quantum conductance oscillations in metal/molecule/metal switches at room temperature

We apply pressure-modulated conductance microscopy to metal/molecule/metal switches. Apart from pressure-induced conductance peaks that indicate nanoscale conducting pathways, we also observe dips and oscillations for devices with conductance between 1 and 2 conductance quantum. The conductance oscillations arise from interfering electron waves along one or two quantum conductance channels between two partially transmitting electrode surfaces at room temperature, underscoring these devices' potential as coherent, atomic-scale switches.     

Perpendicular-current studies of electron transport across metal/metal interfaces

We review what we have learned about the scattering of electrons by the interfaces between two different metals (M1/M2) in the current-perpendicular-to-plane (CPP) geometry. In this geometry, the intrinsic quantity is the specific resistance, AR, the product of the area through which the CPP current flows times the CPP resistance. We describe results for both non-magnetic/non-magnetic (N1/N2) and ferromagnetic/non-magnetic (F/N) pairs. We focus especially upon cases where M1/M2 are lattice matched (i.e., have the same crystal structure and the same lattice parameters to within ∼1%), because in these cases no-free-parameter calculations of 2AR agree surprisingly well with measured values. But we also list and briefly discuss cases where M1/M2 are not lattice matched, either having different crystal structures, or lattice parameters that differ by several percent. The published calculations of 2AR in these latter cases do not agree so well with measured values.     

Dispersion relation for surface plasmon polaritons in metal/nonlinear-dielectric/metal slot waveguides

We present the first (to our knowledge) exact dispersion relation for the transverse-magnetic surface plasmon polariton (SPP) modes of a plasmonic slot waveguide, which is formed by a nonlinear Kerr medium sandwiched between two metallic slabs. The obtained relation is then simplified to the case of small field intensities, while retaining nonlinear terms, to derive approximate dispersion equations for the symmetric and antisymmetric SPP modes.     

Dynamical study on charge injection and transport in a metal/polythiophene/metal structure

The dynamical process of charge injection from metal electrode to a nondegenerate polymer in a metal/polythiophene （PT）/metal structure has been investigated by using a nonadiabatic dynamic approach. It is found that the injected charges form wave packets due to the strong electron-lattice interaction in PT. We demonstrate that the dynamical formation of the wave packet sensitively depends on the strength of applied voltage, the electric field, and the contact between PT and electrode. At a strength of the electric field more than 3.0 × 10^4 V/cm, the carriers can be ejected from the PT into the right electrode. At an electric field more than 3.0 × 10^5 V/cm, the wave packet cannot form while it moves rapidly to the right PT/metal interface. It is shown that the ejected quantity of charge is noninteger.     

Magnetic resonance absorption in isolated metal/insulator/metal nanodot arrays with transmission geometry

In this study, we have systematically investigated a magnetic resonance absorption and tunability of absorption wavelength in isolated metal-insulator-metal (MIM) nanodot arrays with transmission geometry. The elemental electromagnetic resonances and their hybridizations are studied using 3-dimensional finite-difference time-domain (FDTD) calculation and resonance properties including the resonance peak tunability, magnetic permeability and quality (Q) factor are characterized with respect to the coupling strength. We have found the existence of electric and magnetic resonance mode in the MIM (Au/MgF₂/Au) structure and the magnetic resonance has larger wavelength tunability than the electric resonance. The absorption cross section calculation revealed that absorption is the dominant extinction process at the magnetic resonance only. Magnetic permeability (μ) calculations for the various MIM parameters showed the maximum value of the imaginary part of μ is 16.1 with Q factor of 9.2 when the size of nanodot is 200 nm and the inter-dot distance is 300 nm. The presented calculations can be used to tune the response of the magnetic resonance absorption with a variable resonance wavelength and Q factor by using the simple MIM structures with transmission geometry.