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1.
屈光辉  施卫 《物理学报》2006,55(11):6068-6072
利用数值方法对线性条件下横向光电导开关的感生电流和传导电流进行了计算和比较.结果表明在特定的实验条件下,感生电流才会对输出电脉冲产生较大的影响.分析了超快光电导开关在不同实验条件下传导电流与位移电流对输出电脉冲的影响.根据该结论,给出非线性模式下,光电导开关电脉冲超快上升沿小于载流子以饱和速度在电极间渡越所需时间的现象. 关键词: 光电导开关 传导电流 位移电流  相似文献   

2.
We study molecular transistors where graphene nanoribbons act as three metallic electrodes connected to a ring-shaped 18-annulene molecule. Using the nonequilibrium Green function formalism combined with density functional theory, recently extended to multiterminal devices, we show that these nanostructures exhibit exponentially small transmission when the source and drain electrodes are attached in a configuration with destructive interference of electron paths around the ring. The third electrode, functioning either as an attached infinite-impedance voltage probe or as an "air-bridge" top gate covering half of molecular ring, introduces dephasing that brings the transistor into the "on" state with its transmission in the latter case approaching the maximum limit for a single conducting channel device. The current through the latter device can also be controlled in the far-from-equilibrium regime by applying a gate voltage.  相似文献   

3.
We propose a Rashba three-terminal double-quantum-dot device to generate a spin-polarized current and manipulate the electron spin in each quantum dot by utilizing the temperature gradient instead of the electric bias voltage. This device possesses a nonresonant tunneling channel and two resonant tunneling channels. The Keldysh nonequilibrium Green's function techniques are employed to determinate the spin-polarized current flowing from the electrodes and the spin accumulation in each quantum dot. We find that their signs and magnitudes are well controllable by the gate voltage or the temperature gradient. This result is attributed to the change in the slope of the transmission probability at the Fermi levels in the low-temperature region. Importantly, an obviously pure spin current can be injected into or extracted from one of the three electrodes by properly choosing the temperature gradient and the gate voltages. Therefore, the device can be used as an ideal thermal generator to produce a pure spin current and manipulate the electron spin in the quantum dot.  相似文献   

4.
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.  相似文献   

5.
6.
We propose molecular wires based on oligophenyleneimine (OPI) sandwiched between two gold electrodes. The electron transport properties of molecular wires attached to side groups are investigated using steady-state theoretical model and density functional theory by using GAUSSIAN 09 software. We investigate the influence of the side group and torsion angle on the electronic properties of molecular wires. We calculate the spatial distribution of the frontier orbitals, energy gap, transmission probability and the current rectifying ratio for OPI, OPI-pyridine, OPI-pyrazine, OPI-thiophene and OPI-thiazole. The transmission spectra change remarkably depending on the type of side group and torsion angle. The current rectifying ratio will increase by increasing the difference between torsion angles depending on the type of side group. That means the OPI-side group can be employed in molecular electronics.  相似文献   

7.
王瑞  张存喜  周运清  孔令民 《中国物理 B》2011,20(11):117201-117201
We use the transfer matrix method and the Green function technique to theoretically study the quantum tunnelling through a DNA-type molecule. Ferromagnetic electrodes are used to produce the spin-polarized transmission probability and therefore the spin current. The distance-dependent crossover comes from the topological variation from the one-dimensional to the two-dimensional model transform as we switch on the interstrand coupling; a new base pair will present N-1 extrachannels for the charge and spin as N being the total base pairs. This will restrain the decay of the transmission and improve the stability of the quantum transport. The spin and charge transfer through the DNA-type molecule is consistent with the quantum tunneling barrier.  相似文献   

8.
We present molecular dynamics simulations of a realistic model of an ultrathin film of BaTiO3 sandwiched between short-circuited electrodes to determine and understand effects of film thickness, epitaxial strain, and the nature of electrodes on its ferroelectric phase transitions as a function of temperature. We determine a full epitaxial strain-temperature phase diagram in the presence of perfect electrodes. Even with the vanishing depolarization field, we find that ferroelectric phase transitions to states with in-plane and out-of-plane components of polarization exhibit dependence on thickness; it arises from the interactions of local dipoles with their electrostatic images in the presence of electrodes. Secondly, in the presence of relatively bad metal electrodes which only partly compensate the surface charges and depolarization field, a qualitatively different phase with stripelike domains is stabilized at low temperature.  相似文献   

9.
基于直流—射频电极结构对离子的径向和轴向聚焦理论,以离子检测仪器中质子转移反应质谱检测技术为例,对该新型电极结构展开理论和实验研究,相比于静电场电极结构,直流—射频聚焦电场电极结构的性能更好,丙酮产物离子强度提高了近10倍,初步的实验结果表明该结构对于提高离子相对透过率具有较大潜力,同时,该新型直流—射频聚焦电场电极结构对于提高其他类型的离子检测仪器性能将具有一定的应用潜力和参考价值.  相似文献   

10.
We evaluate the full statistics of the current via a Coulomb island that is strongly coupled to the leads. This strong coupling weakens Coulomb interaction. We show that in this case the effects of the interaction can be incorporated into the renormalization of transmission eigenvalues of the scatterers that connect the island and the leads. We evaluate the Coulomb blockade gap in the current-voltage characteristics, the value of the gap being exponentially suppressed as compared to the classical charging energy of the island.  相似文献   

11.
We report first-principles calculations of conductance of carbon nanotubes between metallic electrodes. The electronic states are calculated using a numerical atomic orbital basis set in the framework of the density functional theory, and the conductance is calculated using the Green's function method. We show transmission spectra of carbon nanotubes connected to electrodes and reveal the contact effect of electrodes on the transport properties of nanotubes.  相似文献   

12.
We present an ab initio approach of the electronic transport through a single molecular junction based on C20 fullerene. The electronic properties of a single molecular junction constrained within two semi-infinite metallic electrodes are largely affected by the choice of electrode material. The two-probe device formed by the mechanically control break technique has been modelled with three distinct electrode materials from group IB of the periodic table, namely copper, silver and gold. The quantum characteristics of these mechanically stable devices are obtained by utilising first-principle density functional theory together with non-equilibrium green function method. We evaluate the quantum characteristics, namely density of states, transmission spectrum, energy levels, current and conductance, which essentially determine the behaviour of a molecule linked to different electrodes. Our investigation concludes that copper, silver and gold electrode configuration in conjunction with C20 fullerene behaves as metallic, non-metallic and semi-metallic in nature, respectively.  相似文献   

13.
We investigate the electronic transport properties of photochromic azobenzene-based molecular devices with Au electrodes using non-equilibrium Green’s function and density functional theory. A reversible switching behavior between cis and trans isomerization is found in the device. In addition, the substituent of ?NH2 on the right end hydrogen atom of azobenzene molecule reduces the switching ratio of current, consequently the disappearance of switching behavior, while the substituent of ?NO2 improves the switching ratio of current. We discuss the different electronic transport induced by different substituents through the transmission spectra, localized density of states, molecular projected self-consistent Hamiltonian and transmission pathways. The observed polarization effect under bias is explained by the evolution of molecular projected self-consistent Hamiltonian of LUMO level. The results indicate that the electron-withdrawing group ?NO2 substituting right terminal hydrogen of azobenzene molecule becomes a candidate for improving the performance of molecular device.  相似文献   

14.
We have studied current flow through a single π conjugate molecule weakly adsorbed to, and sandwiched between, two electrodes, focusing specifically on carrier injection through an organic/metal interface. This is the first calculation to investigate the effects of the orientation of the molecule and the electrode material on current using a first-principles method: in the past, most calculations of current were based on the assumption of covalent bonding of a molecule to electrodes. We modeled two systems in which a naphthalene molecule is sandwiched between gold (Au) or aluminum (Al) electrodes. First, in both systems, the current through the molecule depends on the orientation of the molecule. This indicates that electrons mainly transfer through the π channel, which is the overlap between the molecular π orbital and the electrode orbital. Next, the current in the Au-naphthalene-Au system is higher than that in the Al-naphthalene-Al system. This shows that Au is more suitable as an electrode material than Al. Therefore, the orientation of the molecule at an organic/metal interface and the materials comprising the electrodes play a key role in carrier injection through the interface.  相似文献   

15.
We theoretically explore the spin transport through nano-structures consisting of two serially coupled single-molecular magnets (SMM) sandwiched between two nonmagnetic electrodes. We find that the magnetization of SMM can be controlled by the spin transfer torque with respect to the bias voltage direction, and the electron current can be switched on/off in different magnetic structures. Such a manipulation is performed by full electrical manner, and needs neither external magnetic field nor ferromagnetic electrodes in the tunneling junction. The proposal device scheme can be realized with the use of the present technology [6] and has potential applications in molecular spintronics or quantum information processing.  相似文献   

16.
The electronic transport properties of novel NiO monowire connected to the gold electrodes are investigated using density functional theory combined with nonequilibrium Green's functions formalism. The densities of states of the monowire under various bias conditions are discussed. The transport properties are discussed in terms of the transmission spectrum and current–voltage characteristics of NiO monowire. The transmission pathways provide the insight to the transmission of electrons along the monowire. With different bias voltages, current in the order of few microampere flows across the monowire. The applied voltage controls the flow of current through the monowire, which can be used to control the current efficiently in the low order of magnitude in the molecular device.  相似文献   

17.
We propose a system containing a single pyrene molecule sandwiched between two metallic electrodes. The transport properties of the single pyrene molecule with four configurations are investigated using a steady-state theoretical model. We calculate the transmission probability and the electric current for the structure (1, 8), the structure (1, 7), the structure (1, 5) and the structure (1, 4). By applying a gate voltage on the pyrene molecule, we calculate the thermoelectric properties. The thermoelectric and electron transport properties can be controlled by quantum interference, the contact geometry and the gate voltage. The asymmetric behavior and the splitting of resonances in the transmission spectrum occur due to applying a gate voltage on the pyrene molecule. As a result, the structures (1, 5) and (1, 7) have a maximum value of the figure of merit reaching to 0.8 at the Fermi level. According to the results, the structures (1, 5) and (1, 7) can be act as promising thermoelectric applications in molecular electronics.  相似文献   

18.
We demonstrate a high-speed polarization-insensitive photoconductor based on intersecting InP nanowires synthesized between a pair of hydrogenated silicon electrodes deposited on amorphous SiO2 surfaces prepared on silicon substrates. A 14-ps full width at half maximum de-embedded impulse response is measured, which is the fastest reported response for a photodetector fabricated using nanowires. The high-speed electrical signal measurements from the photoconductor are performed by an integrated coplanar waveguide transmission line. The demonstrated ability to grow intersecting InP nanowires on hydrogenated microcrystalline Si surfaces will facilitate the construction of ultra-fast photodetectors on a wide range of substrates. PACS 61.46.Km; 42.70.-a; 81.16.Hc; 81.05.Ea; 85.60.Dw  相似文献   

19.
The coherent potential approximation (CPA) within full counting statistics (FCS) formalism is shown to be a suitable method to investigate average electric conductance, shot noise as well as higher order cumulants in disordered systems. We develop a similar FCS-CPA formalism for phonon transport through disordered systems. As a byproduct, we derive relations among coefficients of different phonon current cumulants. We apply the FCS-CPA method to investigate phonon transport properties of graphene systems in the presence of disorders. For binary disorders as well as Anderson disorders, we calculate up to the 8-th phonon transmission moments and demonstrate that the numerical results of the FCS-CPA method agree very well with that of the brute force method. The benchmark shows that the FCS-CPA method achieves 20 times more speedup ratio. Collective features of phonon current cumulants are also revealed.  相似文献   

20.
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