介电力显微术:一种观察纳米材料中电荷行为的新方法

功能纳米器件中组成材料间的电荷转移输运过程对于器件中的物理化学过程以及由此引发的器件功能会有重大影响,因此,深入理解器件工作过程中的电子/离子行为机理对于优化器件功能以及进一步开发纳米材料的应用潜力具有重要意义.传统场效应晶体管对于纳米材料的电输运测量表征反映了载流子在整个器件中的统计行为,但难以检测电荷具体的转移输运过程.同时,由于纳米材料的尺寸和分散性,基于纳米材料的场效应晶体管面临着制备困难、电极/纳米材料接触复杂和制作成本高等问题.因此,本课题组发展了介电力显微术(dielectric force microscopy,DFM)方法并实现了对纳米材料电学性质的无接触、高空间分辨率和快速表征.本文介绍了介电力显微术的基本原理,列举了其在探究一维纳米材料、纳米颗粒以及有机半导体薄膜电学性质上的一些应用实例.这些实例验证了介电力显微术对纳米材料电学性质的表征能力,并展现了这一技术在纳米材料物理化学性质和纳米器件功能研究上的广阔前景.

Effects of thermal oxidation on microwave-absorbing and mechanical properties of SiC_f/SiC composites with PyC interphase

The SiCf/SiC composites containing PyC interphase were prepared by chemical vapor infiltration process. The influences of thermal oxidation on the complex permittivity and microwave absorption properties of Si Cf/Si C composites were investigated in the frequency range of 8.2-12.4 GHz. Both the real and imaginary parts of the complex permittivity decreased after thermal oxidation. The composites after 100 h thermal oxidation showed that reflection loss exceeded-10 d B in the frequency of 9.7-11.9 GHz and the minimum value was-11.4 d B at 11.0 GHz. The flexural strength of composites decreased but fracture behavior was improved obviously after thermal oxidation. These results indicate that the SiCf/SiC composites containing PyC interphase after thermal oxidation possess good microwave absorbing property and fracture behavior.

Probe the Effects of Surface Adsorbates on ZnO Nanowire Conductivity using Dielectric Force Microscopy

Characterization of electric properties of nanomaterials usually involves fabricating field effect transistors （FET） and deriving materials properties from device performances. However, the quality of electrode contacts in FET devices heavily influences the device performance, which makes it difficult to obtain the intrinsic electric properties of nanomaterials. Dielectric force microscopy （DFM）, a contactless method developed recently, can detect the low-frequency dielectric responses of nanomaterials without electric contact, which avoids the influence of electric contact and can be used to study the intrinsic conductivity of nanomaterials. Here we study the influences of surface adsorbates on the conductivity of ZnO nanowires （NWs） by using FET and DFM methods. The conductivity of ZnO NW is much larger in N2 atmosphere than that in ambient environment as measured by FET device, which is further proven by DFM measurement that the ZnO NW exhibits larger dielectric response in N2 environment, and the influence of electrode contacts on measurement can be ruled out. Based on these results, it can be concluded that the adsorbates on ZnO NW surface highly influence the conductivity of ZnO NW rather than the electrode contact. This work also verifies the capability of DFM in measuring electric properties of nanomaterials.

A Kinetic Model of Dielectric Ageing

A kinetic model of dielectric ageing is presented. The central finding of this investigation is that there is a power-law relationship between the local electric field concentration and the rate of defect-tip initiated conducting crack growth. By applying such a power-law conducting crack growth rate expression to the evaluation of the life of solid dielectrics, the empirical classical ageing law of insulation materials can be derived theoretically as a lobical result. All the results are universal and agree with the experimental data of oxide films.

基于复杂网络理论的舰船电网关键元件辨识方法

舰船电力系统是一种典型的节点紧凑型独立电力系统,其系统容量相对有限,系统元件种类繁杂,电网运行结构灵活多变,电力节点及线路极易遭受战斗损伤。针对舰船电力系统的结构及运行特点,基于复杂网络理论对舰船电网的脆弱性开展研究,建立了舰船电网等效拓扑模型并提出了电力介数指标,实现了对舰船电网中关键元件的辨识。通过对典型舰船电网进行攻击测试,验证了所提出指标的准确性和有效性。

Potassium channel α-subunit AtKC1 negatively regulates AKTl-mediated K^＋ uptake in Arabidopsis roots under Iow-K^＋ stress

Potassium transporters play crucial roles in K^＋ uptake and translocation in plants. However, so far little is known about the regulatory mechanism of potassium transporters. Here, we show that a Shaker-like potassium channel AtKC1, encoded by the AtLKT1 gene cloned from the Arabidopsis thaliana low-K^＋ （LK）-tolerant mutant Atlktl, significantly regulates AKTl-mediated K^＋ uptake under LK conditions. Under LK conditions, the Atkcl mutants maintained their root growth, whereas wild-type plants stopped their root growth. Lesion of AtKC1 significantly enhanced the tolerance of the Atkcl mutants to LK stress and markedly increased K^＋ uptake and K^＋ accumulation in the Atkclmutant roots under LK conditions. Electrophysiological results showed that AtKC1 inhibited the AKT1-mediated inward K^＋ currents and negatively shifted the voltage dependence of AKT1 channels. These results demonstrate that the ‘silent＇ K^＋ channel α-subunit AtKC1 negatively regulates the AKTl-mediated K^＋ uptake in Arabidopsis roots and consequently alters the ratio of root-to-shoot under LK stress conditions.

Effect of MoSi_2 content on dielectric and mechanical properties of MoSi_2/Al_2O_3 composite coatings

Molybdenum disilicide （MoSi2） sheath and aluminum oxide （Al2O3） core blended powders were fabricated by spray drying. A derived coating material was produced for the application as microwave absorbers using the as prepared powders by atmospheric plasma spray （APS） technology. The effects of MoSi2/Al2O3 mass ratio on the dielectric and physical mechanical properties of the composite coatings were investigated. When the MoSi2 content of the composites increases from 0 to 45%, the flexure strength and fracture toughness improve from 198 to 324 MPa and 3.05 to 4.82 MPa-m1/2 then decline to 310 MPa and 4.67 MPa-m1/2, respectively. The dielectric loss tangent increases with increasing MoSi2 content, and the real part of permittivity decreases conversely over the frequency range of 8.2-12.4 GHz. These effects are due to the agglomeration of early molten MoSi2 particles and the increase of the electrical conductivity with increasing MoSi2 content.

The Squeezing Effect in a Mesoscopic RLC Circuit

Using the path integral method we derive quantum wave function and quantum fluctuations of charge andcurrent in the mesoscopic RLC circuit. We find that the quantum fluctuation of charge decreases with time, oppositely,the quantum fluctuation of current increases with time monotonously. Therefore there is a squeezing effect in the circuit.If some more charge devices are used in the mesoscopic-damped circuit, the quantum noise can be reduced. We also findthat uncertainty relation of charge and current periodically varies with the period π/2 in the under-damped case.

FINDING THE OPTIMAL LENGTH OF DATA FRAME IN PLC COMPUTER NETWORK

The length of data frame is an important parameter in Medium Access Control(MAC) layer protocol. A method of finding the optimal length of data frame when impulsive disturbance is involved in PowerLine Communications (PLC) is proposed. Having analyzed the characteristics of impulsive disturbance in powerline and the collision mechanism between the disturbance and data frame, this letter gives the function of the network channel utilization with the length of data frame in MAC layer and the impulsive disturbance. Our stochastic process simulation shows that it is feasible to get the optimal length of data frame.

Oscillatory Behavior of In-medium Interparticle Potential in Hot Gauge System with Scalar Bound States

We investigate the in-medium interparticle potential of hot gauge system with bound states by employing the QED and scalar QED coupling. At the finite temperature an oscillatory behavior of the potential has been found as well as its variation in terms of different free parameters. We expect the competition among the parameters will lead to an appropriate interparticle potential, which could be extended to discuss the fluid properties of QGP with scalar bound states.

Dynamic anti-plane interaction between an impermeable crack and a circular cavity in an infinite piezoelectric medium

Wave propagation in an infinite elastic piezoelectric medium with a circular cavity and an impermeable crack subjected to steady-state anti-plane shearing was studied based on Green's function and the crack-division technique.Theoretical solutions were derived for the whole elastic displacement and electric potential field in the interaction between the circular cavity and the impermeable crack.Expressions were obtained on the dynamic stress concentration factor(DSCF) at the cavity's edge,the dynamic stress intensity factor(DSIF) and the dynamic electric displacement intensity factor(DEDIF) at the crack tip.Numerical solutions were performed and plotted with different incident wave numbers,parameters of piezoelectric materials and geometries of the structure.Finally,some of the calculation results were compared with the case of dynamic anti-plane interaction of a permeable crack and a circular cavity in an infinite piezoelectric medium.This paper can provide a valuable reference for the design of piezoelectric actuators and sensors widely used in marine structures.

Simulation of Influence of Partially Coherent Gaussian Laser Beam on Gradient Force Acting on Dielectric Nanoparticle inside Random Medium

The partially coherent beams propagating through random media have been used in the past to enhance effect of nonlinear optical interaction. Moreover, after propagation through a random （or turbulent） medium the coherent beam becomes a partially coherent one. In this research, the analytical formula for the average intensity of Gaussian beam propagating through random medium is derived and the influence of coherent partiality on optical gradient force acting on dielectric particle rounded by a random media is investigated.

光流体可变光圈的研究现状

光流体可变光圈在图像采集、目标追踪、生物识别和其他便携式电子设备中具有重要的应用潜力。与机械光圈相比,该光圈孔径是近乎完美的可调圆形,且光流体可变光圈具有易于加工、结构紧凑、驱动便捷和功耗低等优点,故已成为当今微纳光学研究领域的热点之一。综述国内外现有光流体可变光圈技术的发展现况,通过总结前人的研究方法,展望未来光流体可变光圈的发展方向。

Effect of mechanical force field on the electromechanical stability of dielectric elastomers

To study the electromechanical stability of dielectric elastomer subjected to a mechanical force field, we use free energy functions of variable forms to analyze the mechanical performance of dielectric elastomer. The relation among critical nominal electric field, critical true electric field, nominal stress and mechanical force field is derived. These calculations agree well with the experimental results. The results can help us better understand the stability conditions of dielectric elastomers and furthermore guide the design and manufacture of sensors and actuators based on dielectric elastomers.

Dielectric barrier plasma dynamics for active aerodynamic flow control

The paper investigates the dynamics of a new multiple bipolar multiple Dielectric Barrier Discharges(DBD)actuator using in large-scale flow control.Particle image velocimetry experiments are performed to characteristic the effectiveness of the multiple bipolar DBD plasma actuator.The results show that the mutual interaction between the electrodes,one major disadvantage of traditional DBD characterized by reverse discharge can be entirely avoided,and a constantly accelerating electric wind velocity can be obtained by using the new multiple bipolar DBD plasma actuator.

Multiple Image Method for the Two Conductor Spheres in a Uniform Electrostatic Field

A method using multiple mirror images of point charges is put forward to analyze the polarization of two identical conductor spheres in a uniform electrostatic field.By use of the method,the electric field distribution and the interaction force between two spheres can be calculated accurately even for very small gap between two spheres.Our results show that the magnitude of the product of the gap between two spheres and the local electric field in the center of the gap is approximately in the same order and the interaction between two spheres increases very fast as the two spheres are close to each other.We also show that the interaction force between two conductor spheres is almost same with that between two dielectric spheres with high permittivity.

Repulsive Casimir Force in a Cavity Comprising a Dielectric with Output Coupling

The Casimir force between a perfectly conducting wall and a dielectric wall in a cavity comprising a transparent dielectric with output coupling is investigated. By using furl quantum theory, we obtain the analysis expression of the force, which shows that the interaction of the two walls in this system is always repulsive. And the value of the Casimir force varies with the field amplitude reflectivity and the cavity size.

Description of squeezed surface plasmons

Surface plasmon polaritons (SPPs) are the combined electron oscillations and electromagnetic waves propagating along the interface between a conductor and a dielectric. Recently Huck et al. [Huck A, et al. Phys Rev Lett, 2009, 102: 246802] proved that SPPs can be in a squeezed state, and the squeezed surface plasmons can propagate in a gold waveguide. In this paper, we introduce a quantum mechanical description of the squeezed surface plasmons at first, and discuss the influence of the waveguide losses on the squeezed surface plasmons.

Constructing hydrophobic protection for ionic interactions toward water,acid,and base-resistant self-healing elastomers and electronic devices

Dynamically crosslinked materials generally lose their self-healing ability and mechanical robustness in aqueous,acidic,and basic environments due to disruption of their dynamic interactions and bonds.Herein,a micelle-like structure with a hydrophobic outer layer is used to protect ionic interactions.This structure ensures the self-healing and long-term stability of the ionically crosslinked elastomers in aqueous,acidic,and basic environments.The elastomer possesses a tensile strength of 6.7 MPa and a strain at break of 1400%,which is superior to the existing waterproof selfhealing elastomers.The strain sensors and dielectric actuators based on the elastomer are highly stable and self-healable,even in extremely harsh environments.This design strategy of hydrophobic protection for dynamic interactions is quite general,allowing it to be extended to other self-healing materials.

In-home Power Line Communication Media Access Control Protocol Based on Collision Resolution

Most existing media access control(MAC) protocols in power line communication(PLC) networks just discard the colliding data packets when collision occurs.The collision deteriorates throughput and delay performance of system under high traffic conditions.This article presents a novel media access scheme with fast collision resolution for in-home power line networks.It works by first recognizing the colliding stations through detecting the inserted unique ID sequence ahead of data packets,then the source nodes retransmitting their packets immediately after the collision slot.The proposed protocol maintains the benefits of ALOHA systems.It needs no scheduling overhead and is suitable for bursty sources,such as multimedia data packets.Computer simulations have demonstrated that this approach can achieve high throughput due to its ability of resolving collisions.