Gate-controlled low-bias rectifying behaviors in BDC60 molecule

Using first-principles density functional theory and non-equilibrium Greenʼs function formalism for quantum transport calculation, we have investigated the effect of gate voltage on the electronic transport properties of BDC60-based molecular junction. The results show that the transport properties are strongly modulated by the applied gate voltage, and the current–voltage curve displays an obvious rectifying behavior at much low bias region. The mechanism for the rectifying behavior is analyzed by the bias-dependent transmission spectrum, projected density of states, spatial distribution of molecular projected self-consistent Hamiltonian orbitals and voltage drop over the junction.     

Carrier transport mechanisms in the ZnO based heterojunctions grown by MBE

This paper presents a review of models of the current transport in different kind of heterojunctions (HJs) and their characteristics. In order to effectively deduce the dominant electron transport for the HJs based on ZnO or Zn_1?xMg_xO layers grown on Si substrate by MBE a comparison is performed – which type of the HJ exhibits better electrical properties. The current–voltage characteristics for the studied HJs were measured within 280–300 K. The transport properties of the HJs are explained in terms of Anderson model with reference to aforementioned current transport models. It is found, that the mechanisms of current transport for all of the studied HJs are similar. At a low forward voltage bias the tunneling current dominates while at medium voltage bias (0.5–1 V) multitunneling capture-emission prevails with the electron trap located at 0.1–0.25 eV below the bottom of a ZnO (Zn_1?xMg_xO) conduction band. Beyond this voltage bias space charge limited current governs the current transport.     

Nanoscale formation mechanism of conducting filaments in NiO thin films

We have studied the nanoscale electrical properties of NiO thin films by using conducting atomic force microscopy (CAFM) to understand the mechanism of resistance change of the NiO thin films as we changed the applied voltage. We observed that inhomogeneous conducting filaments were generated by external voltage bias; in addition, some of the inhomogeneous conducting filaments were durable while some of them were not, and they disappeared. We deduced that the resistance change of the NiO thin films was related to inhomogeneous filamentary conducting paths generated by both Ni ions in thermodynamically unstable NiO and the existence of conducting filament segments generated by high voltage bias.     

Influence of boron distribution on the transport of single-walled carbon nanotube

Using density functional theory combined with nonequilibrium Green’s functions, we investigated and found that boron substitutional doping affects the transport properties of single-walled carbon nanotubes with different distribution. The results reveal that the semiconducting nanotube transits to the quasi-metallic state with nonlinear current–voltage curve after boron doping. Some regular regions of total transmission coefficient with integral values appear with the varying of electron energy and bias voltage. The transport properties of the doped tubes are affected remarkably by the impurity states of quasi-bound defect states which are tuned by the distance between the boron atoms. The current of metallic nanotube is reduced by the impurities and changed with doping patterns. PACS 72.80.Rj; 73.22.2f; 73.61.Wp; 73.63.Rt     

DFT-NEGF study of transport properties and NDR behavior in fused furan and thiophene dimmers

The nonequilibrium Green's function approach in combination with density-functional theory is used to perform quantum mechanical calculations of the electron transport properties of furan and thiophene dimmers. Both the molecular systems have two S-linker and translated into the Gold junction with (1 1 1) surfaces. The studied molecular junctions at zero bias voltage are HOMO-based junctions and currents through these systems are driven by hole transport. The current–voltage characteristics of the both studied molecular junctions illustrate that negative differential resistance (NDR) feature is observed over the bias voltage of 2.0 V. Higher conductivity of fused furan dimmer and NDR character have been explained by the monitoring of the transmission resonance peak across the bias window against varying bias voltages.     

Nonlinear transport through strongly correlated two-terminal heterostructures: a dynamical mean-field approach

The dynamical-mean-field method is applied to investigate the transport properties of heterostructures consisting of a strongly correlated electron system connected to metallic leads. The spectral function inside the correlated region is sensitive to the change of the interaction strength and bias voltage. Because of this sensitivity, current vs voltage characteristics of such heterostructures are rather nonlinear regardless of the detail of the potential profile inside the correlated region. The electronic properties such as the double occupancy are also changed by the bias voltage.     

The comparative study in transport properties of furan, thiophene and selenophene dithiols in nano electronic

The electron transport properties of furan, thiophene and selenophene dithiols based molecular wires through two electrodic systems using non-equilibrium Green’s functions technique (NEGF) are investigated. The electron transport of the above systems is systematically studied by analysis of transmission function, density of states, current–voltage characteristics, and conductance of the systems. The maximum current is occurred at the vicinity of 2.0 V and the values are 90.37, 98.82 and 100.31 μA for furan, thiophene and selenophene dithiols, respectively. These results can be attributed to the molecular projected self consistent Hamiltonian (MPSH) of two electrodic systems with different molecules at different bias voltage and also to quality of resonance of π electrons of heterocyclic ring. We can foresee that the furan, thiophene, and selenophene dithiols can be applied at electronic devices because of switching the high and low current.     

硼氮原子取代掺杂对分子器件负微分电阻效应的影响

利用基于非平衡格林函数和密度泛函理论相结合的第一性原理计算方法,研究了硼氮原子取代掺杂对三并苯分子电子输运性质的影响.计算结果表明,三并苯分子器件的电流在特定偏压区间内随电压的增加而减小呈现出负微分电阻效应,电流的峰谷之比高达5.12.用硼原子或者氮原子取代分子的中心原子后,器件0.8V以内的电流明显增加,但是负微分电阻效应减弱,相应的电流峰谷比分别降至3.83和3.61.分析认为,输运系数在特定偏压下的移动是器件负微分电阻效应的主要成因.核外电子数的差异导致硼氮原子掺杂取代可以使器件轨道及其透射峰分别向高能方向或者低能方向移动从而有效地调控了器件的低偏压下的电子传输能力和负微分电阻效应.     

General transport properties of superconducting quantum point contacts: a Green functions approach

We discuss the general transport properties of superconducting quantum point contacts. We show how these properties can be obtained from a microscopic model using nonequilibrium Green’s function techniques. For the case of a one-channel contact we analyze the response under different biasing conditions: constant applied voltage, current bias and microwave-induced transport. Current fluctuations are also analyzed with particular emphasis on thermal and shot-noise. Finally, the case of superconducting transport through a resonant level is discussed. The calculated properties show a remarkable agreement with the available experimental data from atomic-size contacts measurements. We suggest the possibility of extending this comparison to several other predictions of the theory.     

Fano-type spin-flip mesoscopic transport through an Aharonov-Bohm interferometer

We have investigated the mesoscopic transport properties of a quantum dot embedded Aharonov-Bohm (AB) interferometer applied with a rotating magnetic field. The spin-flip effect is induced by the rotating magnetic field, and the tunneling current is sensitive to the spin-flip effect. The spin-flipped electrons tunneling from the direct channel and the resonant channel interfere with each other to form spin-polarized tunneling current components. The non-resonant tunneling (direct transmission) strength and the AB phase φ play important roles. When the non-resonant tunneling (background transmission) exists, the spin and charge currents form asymmetric peaks and valleys, which exhibit Fano-type line shapes by varying the source-drain bias voltage, or gate voltage. The AB oscillations of the spin and charge currents exhibit distinct dependence on the magnetic flux and direct tunneling strength.     

Electron transport phenomenon simulation through the carborane nano-molecular wire

The electron transport characteristics of a 1,10-dimethylene-1,10-dicarba-closo-decaborane (10-vertex carborane) single molecular conductor is investigated via the density functional-based non-equilibrium Green's function (DFT-NEGF) method. We consider three configurations for the molecular wire sandwiched between two Au(1 0 0) electrodes: the hollow site, top site and bridge site positions. Our results show that the energetically favorable hollow site configuration has a higher current intensity than the other configurations.The projection of the density of states (PDOS) and the transmission coefficients T(E) of the two-probe system at zero bias are analyzed, and it suggests that the variation of the coupling between the molecule and the electrodes with external bias leads to the higher conductance for the hollow configuration.Furthermore, the transmission coefficients of the hollow system at various external voltage biases are also investigated and it shows that the broadening of the transmission coefficient spectrum with increasing of the external voltage bias indicates a strong coupling between the molecular orbitals in the carborane and the incident states from the electrodes, and thus the current increases with increases of the bias voltage.     

Spin polarization of two-dimensional electron gas in hybrid ferromagnetic/semiconductor nanostructures

We present a theoretical study on the spin-dependent transport of electrons in hybrid ferromagnetic/semiconductor nanosystem under an applied bias voltage. Experimentally, this kind of nanosystem can be realized by depositing a magnetized ferromagnetic stripe with arbitrary magnetization direction on the surface of a semiconductor heterostructure. It is shown that large spin-polarized current can be achieved in such a nanosystem. It is also shown that the spin polarity of the electron transport can be switched by adjusting the applied bias voltage. These interesting properties may provide an alternative scheme to realize spin injection into semiconductors, and such a nanosystem may be used as a tunable spin-filter by bias voltage.     

Electron transport properties of stationary plasma clouds generatedwith hollow cathode discharges

The electron transport properties of plasma clouds generated by a hollow cathode discharge are investigated. The voltage-current characteristic curves indicate that the electron-emitted electron current depends on both bias voltage and discharge current. The spatial dependence of the electronic density, plasma potential, and electronic temperature is measured. The energy loss rate of a high energy group of electrons with the radial distance is also presented. These experimental results are compared with a nonisothermal transport model which reproduces the spatial dependence of plasma properties     

Enhancement of bioavailability by formulating rhEPO ionic complex with lysine into PEG–PLA micelle

The electron transport properties of CO adsorbed SiC nanotubes as a function of concentration density and structural deformation have been characterized for the single-walled (7,0) zigzag model using a combined formalism of density-functional theory and nonequilibrium Green’s function. It is found that CO adsorption can significantly suppress the transmission spectrum of SiC nanotube for a wide range of energies. As the concentration increases, a density-dependent superimposed transport gap exists and widens the initial electronic band gap of SiC nanotube. Under the same applied bias voltage, the current through SiC nanotube decreases with the increasing CO concentrations. The local torsional deformation has no effect on this essential motif. However, the current in the locally twisted system is larger than that of the undeformed one. The transmission suppression and the current differences can be attributed to the response of the localized impurity state induced by CO adsorption to density and deformation. Our results show that SiC nanotube can be a promising gas sensor for CO detection.     

Investigation on the electronic transport properties of MgS nanotube based molecular devices – a first-principles study

The electronic transport properties of pure MgS nanotube based molecular devices, Mn-substituted nanotubes and Se-substituted nanotubes are investigated using density functional theory. The state of the art of this work is to study the transport properties of MgS nanotubes with substitution impurities across electrodes. The electronic transport properties are discussed in terms of device density of states and transmission spectrum of MgS nanotubes. The effects of Mn substitution and Se substitution in nanotubes are studied. The major contribution to density of states arises only from p orbitals in MgS nanotubes. The substitution effect and bias voltages also have influence in the density of states. The transmission spectrum provides information about the transmission of electrons along the nanotube. The information provided in this work gives a clear vision to fine-tune MgS nanostructures with improved transport property in nanoelectronic device fabrication.     

Study on typical behavior of transient nature (I-t) and hysterisis nature of I–V characteristics of dye doped solid state thin film photoelectrochemical cell

In this present investigation, we describe the steady state current voltage (I–V) characteristic of Crystal violet dye dispersed solid state photoelectrochemical cell (PEC). Typical behavior of dark current-voltage characteristic by increasing and decreasing external bias voltage has a similar form like hysterisis in nature. Although we have already observed this hysterisis nature in case of both forward and reverse bias condition, yet it is clear that the reverse hysterisis curve is more prominent than forward hysterisis. In this paper, we are getting double values of current (I) for a single value voltage, which is also helpful to understand the charge transport process through disordered materials. As the bias increases, the distribution of traps depth, which is exponential in nature, changes toward order state (resulting increase in disordered parameter α) This means that as α increases, it tends to reach the most order state of material. When external bias voltage is at 3.5 V, the value of disorder parameter becomes 1, and when bias voltage is beyond 3.5 V, the diffusion comes enhanced in nature.     

次近邻跃迁对石墨烯纳米带输运性质的影响

根据紧束缚模型,利用格林函数的方法,将次近邻跃迁考虑在内,研究了扶手椅型石墨烯纳米带的输运性质.通过数值计算,给出了不同尺寸和不同次近邻跃迁能下系统的能量-电导和电流-电压特征曲线.结果表明,次近邻跃迁对扶手椅型石墨烯纳米带的输运性质有显著的影响.它破坏了电导共振峰关于能量的对称分布,增强了系统的导电性,减小了电子导电偏压阈值,加速了系统输运性能由半导体向导体转变. 次近邻跃迁能和石墨烯纳米带的尺寸越大,这种影响越明显     

Field emission and current-voltage properties of boron nitride nanotubes

We have measured electrical transport properties of boron nitride nanotubes using an in situ manipulation stage inside a transmission electron microscope. Stable currents were measured in a field emission geometry, but in contact the nanotubes are insulating at low bias. At high bias, the nanotubes show stable, reversible breakdown current.     

Electronic Transport Calculations Using Maximally-Localized Wannier Functions

I present a method to calculate the ballistic transport properties of atomic-scale structures under bias. The electronic structure of the system is calculated using the Kohn-Sham scheme of density functional theory (DFT). The DFT eigenvectors are then transformed into a set of maximally localized Wannier functions (MLWFs) [N. Marzari and D. Vanderbilt, Phys. Rev. B 56 (1997) 12847]. The MLWFs are used as a minimal basis set to obtain the Hamitonian matrices of the scattering region and the adjacent leads,which are needed for transport calculation using the nonequilibrium Green's function formalism. The coupling of the scattering region to the semi-infinite leads is described by the self-energies of the leads. Using the nonequilibrium Green's function method, one calculates self-consistently the charge distribution of the system under bias and evaluates the transmission and current through the system. To solve the Poisson equation within the scheme of MLWFs I introduce a computationally efficient method. The method is applied to a molecular hydrogen contact in two transition metal monatomic wires (Cu and Pt). It is found that for Pt the I-V characteristics is approximately linear dependence, however, for Cu the I-V characteristics manifests a linear dependence at low bias voltages and exhibits apparent nonlinearity at higher bias voltages. I have also calculated the transmission in the zero bias voltage limit for a single CO molecule adsorbed on Cu and Pt monatomic wires. While a chemical scissor effect occurs for the Cu monatomic wire with an adsorbed CO molecule, it is absent for the Pt monatomic wire due to the contribution of d-orbitals at the Fermi energy.     

Bias Dependence in Spin-Polarized Tunneling of Ferromagnet/Ferromagnetic Insulator (Semiconductor)/Ferromagnet Junctions

Based on the nearly-free-electron approximation, the bias dependencies of electron transport properties of ferromagnet/ferromagnetic insulator (semiconductor)/ferromagnet junctions have been studied. Resonances appear in electron transmission probability. These resonances cause oscillations in the zero-temperature tunnel current and the resonances occur in tunnel conductance. Tunnel magnetoresistance (TMR) is an oscillatory function of bias. The TMR can reach a value as high as 100%. The bins dependencies of electron transport properties relate to the magnetic configurations of the junctions.