耦合形貌对Si4团簇电子输运影响的第一性原理计算

运用密度泛函理论与非平衡格林函数相结合的方法,对Si₄团簇与Au （100）-3×3两电极以顶位-顶位、顶位-空位、空位-空位三种形貌相连构成的Au-Si₄-Au纳米结点的拉伸过程进行第一性原理模拟,计算不同构型纳米结点在不同距离的电导和结合能.讨论耦合形貌、距离对结点电导的影响,结合能的计算表明三种不同耦合形貌结点存在稳定平衡结构,其平衡电导分别为0.71 G₀、0.96 G₀和2.44 G₀,且在-1.2 V~1.2 V的电压范围内,三种不同耦合形貌结点稳定结构表现出类似金属的导电特性,其I-V关系都近似为直线.计算结果表明Si₄团簇与电极的耦合形貌、两极距离对纳米结点电子输运有重要影响.     

非定常输运基于香农熵的自动调整样本数策略

对于非定常输运问题提出了一种基于香农熵的自动调整样本数策略。将每一计算步的总样本数划分为若干批并逐步模拟每批中的粒子, 可以在每批粒子模拟结束后通过计算得到该时间步幸存粒子属性分布对应的香农熵值。采用在线收敛性诊断方法, 一旦通过香农熵值序列判断对应的幸存粒子属性分布已经收敛, 则可以提前结束本时间步的计算。对一个空间一维非定常输运模型的计算结果表明, 该策略可以显著减少每一计算步的实际样本数且保持最终的结果基本不变, 从而减少了计算时间, 提高了计算效率。     

Structural investigation on PEO-based polymer electrolytes dispersed with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

Thin solid polymer electrolytes based on polyethylene oxide (PEO) and silver triflate (AgCF₃SO₃) dispersed with various concentrations of aluminum oxide (Al₂O₃) nanoparticles have been prepared by solution casting technique. These thin polymer films are found to have thickness of the order of 30 to 100 μm. The X-ray diffraction (XRD) patterns have indicated the amorphous nature of the polymer electrolyte. The differential scanning calorimeter (DSC) traces showed slight change in the glass transition temperature (T _g) whereas the degree of crystallization (X _c) decreases markedly due to the addition of alumina nanoparticles. Fourier transform infrared (FTIR) spectral analysis of all these samples has revealed the presence of absorption bands around 1,000 cm⁻¹; thus indicating the complexation of silver ions with oxygen in PEO. Employing the Wagner’s polarization technique as the standard method, the total ionic transference number for the complexed polymer electrolyte was found to be approximately unity thereby revealing that the significant contribution to electrical conduction was due to ions only. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, December 7–9, 2006     

Uphill anomalous transport in a deterministic system with speed-dependent friction coefficient

We investigate the transport of a deterministic Brownian particle theoretically, which moves in simple onedimensional, symmetric periodic potentials under the influence of both a time periodic and a static biasing force. The physical system employed contains a friction coefficient that is speed-dependent. Within the tailored parameter regime, the absolute negative mobility, in which a particle can travel in the direction opposite to a constant applied force, is observed.This behavior is robust and can be maximized at two regimes upon variation of the characteristic factor of friction coefficient. Further analysis reveals that this uphill motion is subdiffusion in terms of localization(diffusion coefficient with the form D(t) ~t~(-1) at long times). We also have observed the non-trivially anomalous subdiffusion which is significantly deviated from the localization; whereas most of the downhill motion evolves chaotically, with the normal diffusion.     

On the lattice Boltzmann method for phonon transport

The lattice Boltzmann method is a discrete representation of the Boltzmann transport equation that has been employed for modeling transport of particles of different nature. In the present work, we describe the lattice Boltzmann methodology and implementation techniques for the phonon transport modeling in crystalline materials. We show that some phonon physical properties, e.g., mean free path and group velocity, should be corrected to their effective values for one- and two-dimensional simulations, if one uses the isotropic approximation. We find that use of the D2Q9 lattice for phonon transport leads to erroneous results in transient ballistic simulations, and the D2Q7 lattice should be employed for two-dimensional simulations. Furthermore, we show that at the ballistic regime, the effect of direction discretization becomes apparent in two dimensions, regardless of the lattice used. Numerical methodology, lattice structure, and implementation of initial and different boundary conditions for the D2Q7 lattice are discussed in detail.     

Hopping Transport and Stochastic Dynamics of Electrons in Plasma Layers

We investigate the stochastic dynamics and the hopping transfer of electrons embedded into two‐dimensional atomic layers. First we formulate the quantum statistics of general atom ‐ electron systems based on the tight‐binding approximation and express ‐ following linear response transport theory ‐ the quantum‐mechanical time correlation functions and the conductivity by means of equilibrium time correlation functions. Within the relaxation time approach an expression for the effective collision frequency is derived in Born approximation, which takes into account quantum effects and dynamic effects of the atom motion through the dynamic structure factor of the lattice and the quantum dynamics of the electrons. In the last part we derive Pauli equations for the stochastic electron dynamics including nonlinear excitations of the atomic subsystem. We carry out Monte Carlo simulations and show that mean square displacements of electrons and transport properties are in a moderate to high temperature regime strongly influenced by by soliton‐type excitations and demonstrate the existence of percolation effects (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Collective Diffusion and Strange-Metal Transport

We study a particular combination of charge and heat currents, which is decoupled with the heat current. The "heat-decoupled" (HD) current can be transported by diffusion at long distances, when the thermoelectric effect is small, large, or balanced. Using holographic models with momentum relaxation, we illustrate that the different thermoelectric effects correspond to the high temperatures and strong disorder, low temperatures, or special critical index. Meanwhile, the Einstein-like relation and the diffusion/chaos relation may be emergent. Assuming that the existence and features of HD modes appear in strange metals, we can predict that when the thermoelectric effect is not very large, the scaling of resistivity is predominantly controlled by the HD susceptibility and chaos; otherwise more physics is required.     

电纺ZnO纳米纤维电子传输层提高倒置PTB7∶PC70BM电池效率

研究利用静电纺丝制备的不同直径ZnO纳米纤维作为倒置结构有机太阳能电池的电子传输层对器件转化效率的影响。首先通过静电纺丝技术成功制备了半径在43～110 nm之间的ZnO纳米纤维,然后将ZnO纳米纤维作为电子传输层加入到倒置结构有机太阳能电池（ITO/ZnO∶ZnO nanofiber/PTB7∶PC₇₀BM/MoO₃/Al）。与平面结构的ZnO电子传输层相比,ZnO纳米纤维具有比表面积大等优点,增加了电子传输和抽取能力,提高了器件的光电转化效率。实验发现ZnO纳米纤维的直径越小,电池效率越大。当ZnO纳米纤维直径为(46±5)nm,接收时间为30 s时,作为电子传输层的电池效率提高了8%。     

MgB2超导圆线基底交流损耗的计算分析

二硼化镁(MgB2)超导体在非铜氧化物陶瓷超导体中具有最高临界转变温度,给超导应用带来了新的契机.铁与镁不反应,且价格低廉,在需要热处理的超导成材工艺中,常常采用铁作MgB2的基底;然而,这种高磁导率的材料有可能增大基底的损耗.本文采用有限元分析软件ANSYS计算了工频下不同材料基底超导圆线传输交流的基底损耗,分析了基底损耗与电流大小、基底厚度之间的关系,对双层基底的损耗也进行了研究.本文的结果对于适当选取截面尺寸、基底材料和工作电流以期减小交流损耗,具有一定参考意义.     

有机/无机复合双层电子传输层的量子点发光二极管

采用有机/无机复合双层电子传输层（ETL）研制绿色QLEDs,其中有机ETL采用OLED中常见的ETL材料,无机ETL采用ZnO纳米颗粒,并通过调控有机ETL厚度改变电子注入,使电子/空穴达到平衡。制备的器件结构为:ITO/PEDOT:PSS/TFB/QDs/ZnO NPs/TPBI:Liq/Al,其中有机电子传输层TPBI:Liq采用真空蒸镀沉积。与仅采用ZnO电子传输层的器件相比,可以使器件性能得到大幅提升:器件的最大电流效率从11.53 cd/A提升到22.77 cd/A,同时器件的启亮电压、电致发光光谱无明显变化。判断有机ETL的主要作用是抑制了过量电子的注入和传输,在发光亮度变化不大的情况下,降低了器件的无效复合（例如俄歇复合）电流,从而使电流效率明显提升。