C59N单分子整流器

通过将单个C59N分子置于双势垒隧道结中，从而利用单电子隧穿效应和C59N分子的特殊能级结构，我们成功地实现了一种新型的单分子整流器件．实验中这个整流器件的正向导通电压约为0．5-0．7V，反向击穿电压约为1．6—1．8V．理论分析表明，中性C59N分子的半占据费米能级以及在不同充电情况下费米能级的不对称移动是形成整流效应的主要原因．其构成原理也决定了该器件具有稳定、易重复的特点．     

低阈值极化电压玻璃光波导电光效应的研究(英文)

采用热极化技术对掺锗玻璃条形光波导进行极化,通过光纤连接(单模)的Mach ZehnderInterferometer系统测量条形波导内诱导出的电光效应,系统地研究了大气环境下极化条件(极化温度、极化时间、极化电压)对电光效应的影响.结果表明:在最佳极化条件下(406℃、-2.4kV、20min),波导内的电光系数为rTM=0.059±0.001pm/V,rTE=0.053±0.001pm/V,且波导结构中存在一个较低的阈值极化电压(100V)和阈值极化温度(80℃),此时在波导样品内仍能被激发出可观察的电光效应;实验还发现采用负极化诱导方式产生的电光系数较正极化提高15%左右.     

低阈值极化电压玻璃光波导电光效应的研究

采用热极化技术对掺锗玻璃条形光波导进行极化,通过光纤连接 (单模) 的Mach Zehnder Interferometer 系统测量条形波导内诱导出的电光效应,系统地研究了大气环境下极化条件(极化温度、极化时间、极化电压)对电光效应的影响.结果表明:在最佳极化条件下(406℃、-2.4 kV、20 min),波导内的电光系数为r_TM=0.059±0.001 pm/V, r_TE=0.053±0.001 pm/V,且波导结构中存在一个较低的阈值极化电压(100 V)和阈值极化温度(80℃),此时在波导样品内仍能被激发出可观察的电光效应;实验还发现采用负极化诱导方式产生的电光系数较正极化提高15%左右.     

Low-bias negative differential conductance controlled by electrode separation

The electronic transport properties of a single thiolated arylethynylene molecule with 9,10-dihydroanthracene core,denoted as TADHA, is studied by using non-equilibrium Green's function formalism combined with ab initio calculations.The numerical results show that the TADHA molecule exhibits excellent negative differential conductance(NDC) behavior at lower bias regime as probed experimentally. The NDC behavior of TADHA molecule originates from the Stark effect of the applied bias voltage, by which the highest occupied molecular orbital(HOMO) and the HOMO-1 are pulled apart and become localized. The NDC behavior of TADHA molecular system is tunable by changing the electrode distance.Shortening the electrode separation can enhance the NDC effect which is attributed to the possible increase of coupling between the two branches of TADHA molecule.     

Spin-dependent rectification in the C 59 N molecule

Coherent spin-dependent electron transport is investigated in three conditions: (1) a C₆₀ molecule is connected to two ferromagnetic (FM) electrodes symmetrically, (2) a C₅₉N molecule is connected to two FM electrodes symmetrically and (3) a C₅₉N molecule is connected to two FM electrodes asymmetrically. This work is based on a single-band tight-binding model Hamiltonian and the Green’s function approach with the Landauer–Buttiker formalism. Electrodes used in this study are semi-infinite FM electrodes with finite cross-section. Obvious rectification effect is observed in the C₅₉N molecule which is connected to the FMelectrodes asymmetrically. This effect is more in the P alignment of FM electrodes than in AP alignment of FM electrodes. This study indicates that the rectification behaviour is due to the asymmetry in molecule and junctions. Also in this investigation tunnel magnetoresistance (TMR) is calculated for these molecules. Asymmetry is observed in TMR of C₅₉N which is coupled to the electrodes asymmetrically due to asymmetric junctions, but TMR of C₆₀ is symmetric.     

Pulsed generation of an electrical voltage at the thermovoltaic effect in SmS

The thermovoltaic effect in SmS is measured at elevated frequencies near 1000 Hz. Pulsed generation of an electrical voltage at this effect is discovered and explained. The maximal value of the generated voltage and the power of the generated signal are measured to be 6.3 V and about 1 W, respectively. These values are attained at about 130°C.     

用发射光谱法测量氮气直流辉光放电的转动温度

本文报道了氮气气压分别为10和20Pa时，对直流辉光放电的发射光谱进行测量和分析的结果。选择的研究对象为N2放电中形成的N2^ B^2∑u^ →X^2∑g^ 跃迁的Δv=v′-v″=0谱带系中v′=0→v″=0谱带的R支。在阴极背面辉光区、阴极鞘层区、正柱区以及阳极辉光区中分别选择一点进行了转动分辨的发射光谱的测量。利用自己编写的光谱拟合程序，获得了相应的实验条件下N2^ 的转动温度，给出了转动温度随放电电压的变化趋势，其结果可以用直流放电的帕邢定律得到很好的解释。在10和20Pa气压下，放电的阴极鞘层区、正柱区、阳极辉光区中的转动温度都随放电电压呈现出了不同的变化趋势，甚至是完全相反的变化趋势。我们认为这是由于气压不同时，放电状态不同所致：气压为10Pa时的放电是正常辉光放电，而气压为时20Pa的放电为反常辉光放电。     

ZnCdTe-ZnTe多量子阱的电场效应

本文报导了电场作用下ZnCdTe-ZnTe多量子阱的激子发光特性.用激子局域化的观点解释了激子发光峰随电场增强而增强的现象.在Zn0.8Cd0.2Te-ZnTe多量子阱中观察到了电场作用下自由激子发光谱峰较大的红移和较快的发光淬灭     

Adsorption and rotational barrier for a single azobenzene molecule on Au(111) surface

The orientation switching of a single azobenzene molecule on Au(111) surface excited by tunneling electrons and/or photons has been demonstrated in recent experiments. Here we investigate the rotation behavior of this molecular rotor by first-principles density functional theory(DFT) calculation. The anchor phenyl ring prefers adsorption on top of the fcc hollow site, simulated by a benzene molecule on close packed atomic surface. The adsorption energy for an azobenzene molecule on Au(111) surface is calculated to be about 1.76 e V. The rotational energy profile has been mapped with one of the phenyl rings pivots around the fcc hollow site, illustrating a potential barrier about 50 me V. The results are consistent with experimental observations and valuable for exploring a broad spectrum of molecules on this noble metal surface.     

衰减全反射型电压传感器的理论和实验研究

提出了一种新型反射型聚合物波导电压传感器理论,并且进行了实验研究。这种电压传感器采用棱镜波导耦合结构,在棱镜下底面依次镀有金属膜一聚合物一金属膜三层结构。通过两层金属膜对极化聚合物加电压,利用聚合物材料电光效应和导模共振吸收峰对聚合物折射率的敏感特性,通过反射光强的测量来确定作用电压的变化值。实验中的测试电压范围是从-140V至 140V,得到的线性度值为0．991,电压测量的分辨力为0．1V,电压测量灵敏度系数为0．0011V^-1。实验表明这种电压传感器具有良好的线性和较高的灵敏度。     

离子(N2+, N+)在氮辉光放电等离子体光辐射中的作用

采用氮辉光放电等离子体电子与重粒子综合的Monte Carlo模型,研究了离子(N2+,N+)与氮分子碰撞产生光辐射的强度分布及其 在氮辉光放电等离子体光辐射中的作用。两种离子产生的各种碰撞激发和辐射都分布在鞘层区内,光辐射强度向阴极方向逐渐 增加,且总强度随放电电压增加而增强。相对于电子产生的碰撞激发辐射,离子(N2+,N+)引起的辐射在阴极附近引起次最大 光强,且原子离子N+的作用较分子离子N2+大。当电压较低时,离子(N2+,N+)引起的辐射可以忽略。模拟结果很好解释了两 种典型的N2辉光放电光学发射谱的实验结果,为等离子体诊断研究中的光谱数据分析提供参考。     

外场对分子纳米结电流-电压特性的影响

针对由金属电极/分子/金属电极组成的分子纳米结,应用扩展主方程的方法,考虑分子纳米结中影响其传输过程的外场、分子内的弛豫过程等因素研究了在外场作用下分子纳米结内的稳定电流和瞬间电流.由于分子内较强的电子-振动耦合,分子纳米结中的电流-电压曲线呈现台阶式非弹性特征.在不同的高斯型脉冲的激发作用下,分子纳米结中电流需要达到稳定的时间也不相同,脉冲宽度在1ps时瞬间电流现象明显,这时分子处于非平衡分布,分子两端的电流存在较大差异.随着脉冲宽度和外场偏压的增加,分子两端的电流趋于平衡.     

Effects of electron-vibration coupling in transport through single molecules

Using scanning tunneling spectroscopy, we study the transport of electrons through C(60)?molecules on different metal surfaces. When electrons tunnel through a molecule, they may excite molecular vibrations. A fingerprint of these processes is a characteristic sub-structure in the differential conductance spectra of the molecular junction reflecting the onset of vibrational excitation. Although the intensity of these processes is generally weak, they become more important as the resonant character of the transport mechanism increases. The detection of single vibrational levels crucially depends on the energy level alignment and lifetimes of excited states. In the limit of large current densities, resonant electron-vibration coupling leads to an energy accumulation in the molecule, which eventually leads to its decomposition. With our experiments on C(60)?we are able to depict a molecular scale picture of how electrons interact with the vibrational degrees of freedom of single molecules in different transport regimes. This understanding helps in the development of stable molecular devices, which may also carry a switchable functionality.     

ZnO半导体电导型X射线探测器件研究

本文制备了基于ZnO纳米线阵列和ZnO薄膜的Ag-ZnO-Ag电导型X射线探测器件,研究了它们对X射线的响应特性.薄膜器件在100 V偏置时的响应度达到0.12μC/Gy,纳米线阵列器件在50 V偏压下的响应度达到0.17μC/Gy.器件工作机理研究表明,器件的响应过程与表面氧吸附与解吸附效应有关,氧气吸附与解吸附过程使得X射线辐照下的载流子寿命大幅度增加,从而使得器件对X射线具有较高的响应度.本文研究结果表明ZnO薄膜和纳米线阵列器件在X射线剂量测量领域具有应用前景.     

Effect of 30 Mev Li 3+ ion and 8 MeV electron irradiation on n-channel MOSFETs

The effect of 30 v MeV Li 3+ ion and 8 v MeV electron irradiation on the threshold voltage ( V TH ), the voltage shift due to interface trapped charge ( j V Nit ), the voltage shift due to oxide trapped charge ( j V Not ), the density of interface trapped charge ( j N it ), the density of oxide trapped charge ( j N ot ) and the drain saturation current ( I D v Sat ) were studied as a function of fluence. Considerable increase in j N it and j N ot , and decrease in V TH and I D v Sat were observed in both types of irradiation. The observed difference in the properties of Li 3+ ion and electron irradiated MOSFETs are interpreted on the basis of energy loss process associated with the type of radiation. The study showed that the 30 v MeV Li 3+ ion irradiation produce more damage when compared to the 8 v MeV electron irradiation because of the higher electronic energy loss value. High temperature annealing studies showed that trapped charge generated during ion and electron irradiation was annealed out at 500 v °C.     

Electron delocalization and dimerization in solid C59N doped C60 fullerene

Electron spin resonance and ab initio electronic structure calculations show an intricate relation between molecular rotation and chemical bonding in the dilute solid solution. The unpaired electron of C59N is delocalized over several C60 molecules above 700 K, while at lower temperatures it remains localized within short range. The data suggest that below 350 K rigid C59N-C60 heterodimers are formed in thermodynamic equilibrium with dissociated rotating molecules. The structural fluctuations between heterodimers and dissociated molecules are accompanied by simultaneous electron spin transfer between C60 and C59N molecules. The calculation confirms that in the C59N-C60 heterodimer the spin density resides mostly on the C60 moiety, while it is almost entirely on C59N in the dissociated case.     

A method for continuous monitoring of quantum tunneling in a molecular double dot

An application of impedance measurement technique (IMT) for a detection of quantum tunneling in molecular structures is investigated. A charged particle which tunnels in a two-well potential is electrically coupled to a high-quality superconducting LC-circuit (tank) that makes possible a measurement of the electric susceptibility of the molecule at the resonant frequency of the tank. The real part of this susceptibility bears information about the tunneling rate through a measurable parameter—a phase angle between the tank voltage and a bias current applied to the tank. It is shown that the present approach is highly sensitive and allows the monitoring of the tunnel motion of charged nuclei in a single molecule.     

Conductance through glycine in a graphene nanogap

We report theoretical analysis of charge transport process through a single glycine molecule utilizing graphene nanogaps. Density functional theory and non-equilibrium Green’s function method are employed to investigate the transport properties of glycine inside the gap. The projected density of states, transmittance, and the current–voltage characteristics are determined with changes in the molecular orientation inside the nanogap of c.a 0.8 nm. The current values demonstrate a high sensitivity on the orientation of the molecule. The conductance of the molecule is also dependent on the voltage.     

A High Performance Terahertz Waveguide Detector Based on a Low-Barrier Diode

A Schottky barrier diode with low-barrier is presented,based on which a terahertz waveguide detector working at500-600 GHz is designed and fabricated.By using the InGaAs/InP material system,the feature of the low barrier is obtained which greatly improves the performance of the detector.The measured typical voltage responsivity is about 900 V/W at 500-560 GHz and is about 400 V/W at 560-600 GHz.The proposed broadband waveguide detector has the characteristics of simple structure,compact size,low cost and high performance,and can be used in a variety of applications such as imaging,molecular spectroscopy and atmospheric remote sensing.     

Preferred orientations of encapsulated C60 molecules inside single wall carbon nanotubes

A systematical study of the orientational behavior of C60 molecules in single wall carbon nanotubes (SWCNTs) with different chirality and diameter has been performed by using a model of an infinite long nanotube filled with two C60 (denoted as C60-1 and C60-2) molecules. We studied the preferred orientation of the C60-1 molecule when the neighboring C60-2 molecule was fixed at the pentagon, double-bond, and hexagon orientations respectively. Our results showed that the C60-1 molecule prefers the pentagon (hexagon) orientation when the tube diameter is smaller (larger) than 1.31nm (1.36nm). For the tube diameter in between, the preferred molecular orientation of C60-1 changes from pentagon to hexagon with the increasing tube diameter when the neighboring C60-2 molecule is fixed at the pentagon or double-bond orientation. A novel vertex orientation for the C60-1 molecule has been found when the C60-2 molecule is fixed at the hexagon orientation.