Absorption Range and Energy Shift of Surface Plasmon in Au Monomer and Dimer

The resonance behaviors of local surface plasmon resonance in Au monomer and dimer are characterized systemically by electron energy loss spectroscopy in a scanning transmission electron microscope.The measured absorption range is about 20 nm larger than the physical size of the Au nanoparticles and the resonance peak energy shows a red shift when the electron beam passes off the nanoparticles.The Au dimer displays similar behaviors.Numerical simulation also reproduces those experimental results.     

Resonant tunneling though an asymmetrical two-magnetic-barrier structure on single layer graphene

The transmission probability against the electron normal incident energy through an asymmetrical two-magnetic-barrier structure of single layer graphene has been investigated and presented. One barrier’s height and width are varied while those of the other are kept at constant values. The effect of the structural asymmetry on the resonance energy and the resonant transmission peak value are also systematically studied with the help of numerical calculations based on the transfer matrix method. Investigations show that the unity transmission occurs in an asymmetrical two-magnetic-barrier structure when both the phase difference condition for resonance (PDCR) and the maximum condition for the resonance peak value (MCPV) are satisfied simultaneously. However, PDCR underestimates the resonance energy of an asymmetrical two-magnetic-barrier structure, and the deviation becomes more obvious as the structure progressively becomes less symmetrical. These findings are believed to be of significant importance for the design of single layer graphene based devices.     

Interpreting electron transmission spectroscopy and negative ion mass spectrometry data using a spherical potential well model

Experimental data obtained using electron transmission spectroscopy and negative ion mass spectrometry based on resonance electron capture are interpreted within the framework of a spherical potential well model in application to a series of chloro-and bromoalkane molecules. Allowance for the scattering of a single partial p-wave of the incoming electron makes possible (i) reproduction of the ratio of a resonance peak width to the electron energy observed in the electron transmission spectra and (ii) establishment of a relation between the total cross section of electron scattering on a molecule and the dissociative electron attachment cross section. The proposed model offers a radical simplification of the approach developed previously based on the Fashbach-Fano resonance theory.     

考虑透射概率的能量选择性电子热泵

研究了具有不同温度和不同化学势的两个热库中的电子通过一个能量透射谱进行传输的问题,得到电子通过能量透射谱传输所产生的热流.进一步考虑了两个热库之间的辐射热漏流,数值计算出电子热泵的性能参数,绘出了热泵的性能特征曲线.分析了热漏、共振中心能级位置和能级宽度等参数对热泵工作性能的影响.当共振能级宽度无限小时,热泵系数可以达到Carnot值.     

考虑透射概率的能量选择性电子热泵

研究了具有不同温度和不同化学势的两个热库中的电子通过一个能量透射谱进行传输的问题,得到电子通过能量透射谱传输所产生的热流.进一步考虑了两个热库之间的辐射热漏流,数值计算出电子热泵的性能参数,绘出了热泵的性能特征曲线.分析了热漏、共振中心能级位置和能级宽度等参数对热泵工作性能的影响.当共振能级宽度无限小时,热泵系数可以达到Carnot值. 关键词： 透射谱 态密度 辐射热漏 电子热泵     

Electronic transport through a periodic array of quantum-dot rings

Using the tight-binding approximation and the transfer matrix method, this paper studies the electronic transport properties through a periodic array of quantum-dot (QD) rings threaded by a magnetic flux. It demonstrates that the even--odd parity of the QD number in a single ring and the number of the QD rings in the array play a crucial role in the electron transmission. For a single QD ring, the resonance and antiresonance transmission depend not only on the applied magnetic flux but also on the difference between the number of QDs on the two arms of the ring. For an array of QD rings, the transmission properties are related not only to the even--odd parity of the number $N_{0}$ of QDs in the single ring but also to the even--odd parity of the ring number $N$ in the array. When the incident electron energy is aligned with the site energy, for the array of $N$ rings with $N_{0}={\rm odd}$ the antiresonance transmission cannot occur but the resonance transmission may occur and the transmission spectrum has $N$ resonance peaks ($N-1$ resonance peaks) in a period for $N={\rm odd}$ (for $N={\rm even}$). For the array of $N$ rings with $N_{0}={\rm even}$ the transmission properties depend on the flux threading the ring and the QD number on one arm of the ring. These results may be helpful in designing QD devices.     

N重方势垒结构共振隧道效应研究

本文从理论上研究了N重方势垒结构的共振隧道效应,推导出透射系数及共振隧道条件的解析表达式,结果发现,由于多势垒结构(n≥3)量子阱间的耦合,共振能级不同于量子阱的本征值。此外,由透射系数表示式证实了多势垒结构电子透射谱在共振能级附近为Lorentzian型。所得结果对于分析透射系数随能量的变化关系,估计共振能级以及制造共振隧道器件都具有十分重要的意义。 关键词：     

Spin-dependent resonant tunneling in a periodic non-magnetic heterostructure with spin-orbit effects

We theoretically investigate the electron transport in a periodic non-magnetic heterostructure with both Dresselhaus and Rashba spin-orbit effects. We show that the transport properties obviously depend on the number of periods and the large spin polarization can be achieved in such a structure. We also show that for m>1, the resonance splitting occurs in the transmission curves of both spin-up and spin-down electrons when the transmission curves are plotted as a function of the electron energy or the well width.     

The effect of non-constant effective tunneling mass and asymmetry for resonant tunneling in double-barrier structures

We discuss the transmission coefficient τ_d in non-repetitive, one-dimensional, rectangular double-barrier structures without simplifications such as strongly attenuating barriers, strong localization, or overall constant effective tunneling mass of the electron. For resonance τ_d=1, we obtain two non-approximative conditions which require different resonance energies of the tunneling electron than previously reported in the literature. In fact, the resonance peaks are shifted to higher energy levels in the order of the width of the peaks due to the effect of non-constant tunneling mass. We investigate the dependence of the resonance condition and the shape of the resonance peaks in regard to perturbation of the electron energy, the gap width as well as the barrier width and height. Resonance is stable for variation of the barrier width but sensitive for variation of the barrier height and the gap width. Received: 9 December 1998 / Accepted: 5 January 1999 / Published online: 31 March 1999     

Doublet resonances of an electron in symmetric three-barrier resonant tunneling structures

The evolution and collapse of electron resonances and their spectral parameters in a symmetric three-barrier resonant tunneling structure (TBRTS) are studied theoretically. The resonance energy and width of the quasi-stationary states of an electron are analyzed. The quasi-stationary states are calculated by the transmission coefficient method, the method of the probability distribution function (the probability of finding an electron in a TBRTS), and the scattering cross section method.     

Field-assisted spin-polarized electron transport through a single quantum well with spinben orbit coupling

We have investigated theoretically the field-driven electron transport through a single-quantum-well semiconductor heterostructure with spin-orbit coupling. The splitting of the asymmetric Fano-type resonance peaks due to the Dresselhaus spin-orbit coupling is found to be highly sensitive to the direction of the incident electron. The splitting of the Fano-type resonance induces the spin-polarization dependent electron current. The location and the line shape of the Fano-type resonance can be controlled by adjusting the energy and the direction of the incident electron, the oscillation frequency, and the amplitude of the external field. These interesting features may be used to devise tunable spin filters and realize pure spin transmission currents.     

Resonant Multichannel Scattering in a Nanotube with δ-Potentials

The resonant tunneling transmission of an electron through the quantum wire comprising two three-dimensional δ-potentials located along the nanotube axis is considered. Using the formulas obtained recently for amplitudes of multichannel scattering, the condition (equation) of resonance is found for the multichannel scattering, at which the system under consideration becomes completely transparent for motion of the electron. A procedure based on the method of vector diagrams is proposed for simplification of the resonance equation. It is shown that if the initial energy of longitudinal motion is insufficient for excitation of new scattering channels, then the resonance equation coincides with the corresponding equation of one-dimensional problem.     

Field-assisted spin-polarized electron transport through a single quantum well with spin-orbit coupling

We have investigated theoretically the field-driven electron transport through a single-quantum-well semiconductor heterostructure with spin-orbit coupling.The splitting of the asymmetric Fano-type resonance peaks due to the Dresselhaus spin-orbit coupling is found to be highly sensitive to the direction of the incident electron.The splitting of the Fano-type resonance induces the spin-polarization dependent electron current.The location and the line shape of the Fano-type resonance can be controlled by adjusting the energy and the direction of the incident electron,the oscillation frequency,and the amplitude of the external field.These interesting features may be used to devise tunable spin filters and realize pure spin transmission currents.     

自旋轨道耦合Su-Schrieffer-Heeger原子链系统的电子输运特性

在Su-Schrieffer-Heeger (SSH)原子链中,电子在胞内和胞间的跳跃依赖于其自旋时,即SSH原子链存在自旋轨道耦合作用时,存在不同缠绕数的非平庸拓扑边缘态.如何探测自旋轨道耦合SSH原子链不同缠绕数的边缘态是一个重要问题.本文在紧束缚近似下研究了自旋轨道耦合SSH原子链的非平庸拓扑边缘态性质及其零能附近的电子输运特性.研究发现四重和二重简并边缘态的缠绕数分别为2和1;并且仅当源极入射电子的自旋被极化(铁磁电极)时,自旋轨道耦合SSH原子链在零能附近的电子输运特性才能反映其边缘态的能谱特性.尤其是,随着自旋轨道耦合SSH原子链与左、右导线之间的耦合强度由弱到强改变,对于缠绕数为2的四重简并边缘态,入射电子在零能附近的透射峰数目将从4个变为0;而对于缠绕数为1的二重简并边缘态情形,其透射峰数目将从2个变为0.因此,在源极为铁磁电极的情形下,通过观察自旋轨道耦合SSH原子链在零能附近电子共振透射峰的数目随着其与左、右导线之间耦合强度的变化,来探测其不同缠绕数的边缘态.上述结果为基于电子输运特性探测自旋轨道耦合SSH原子链不同拓扑性质的边缘态提供了一种可选择的理论方案.     

The electron transport characters in a nanostructure with the periodic magnetic-electric barriers

This paper detailedly studies the transmission probability, the spin polarization and the conductance of the ballistic electron in a nanostrueture with the periodic magnetic-electric barriers These observable quantities are found to be strongly dependent not only on the magnetic configuration, the incident electron energy and the incident wave vector, but also on the number of the periodic magnetic-electric barriers The transmission coefficient and the spin polarization show a periodic pattern with the increase of the separation between two adjacent magnetic fields, and the resonance splitting increases as the number of periods increases. Surprisingly, it is found that a polarization can be achieved by spin-dependent resonant tunnelling in this structure, although the average magnetic field of the structure is zero.     

The electron transport characters in a nanostructure with the periodic magnetic-electric barriers

This paper detailedly studies the transmission probability, the spin polarization and the conductance of the ballistic electron in a nanostructure with the periodic magnetic-electric barriers. These observable quantities are found to be strongly dependent not only on the magnetic configuration, the incident electron energy and the incident wave vector, but also on the number of the periodic magnetic-electric barriers. The transmission coefficient and the spin polarization show a periodic pattern with the increase of the separation between two adjacent magnetic fields, and the resonance splitting increases as the number of periods increases. Surprisingly, it is found that a polarization can be achieved by spin-dependent resonant tunnelling in this structure, although the average magnetic field of the structure is zero.     

多元纳米稀土六硼化物Nd1-xEuxB6粉末的制备及光吸收研究

在真空环境中采用固相烧结法成功制备出了多元稀土六硼化物Nd1-xEuxB6纳米粉末.系统研究了Eu掺杂对纳米NdB6物相、形貌及光吸收性能的影响规律.结果表明,所有合成的纳米粉末物相均为单相的CsCl型晶体结构,具有立方形貌,平均晶粒尺度为30 nm.光吸收实验结果表明,随着Eu掺杂量的增加,纳米NdB6透射光波长从629 nm红移至1000 nm以上,表现出了透射光波长的可调特性.此外,NdB6和EuB6同步辐射吸收图谱表明,Nd和Eu原子分别以Nd^3+和Eu^2+形式存在于纳米NdB6和EuB6中,充分说明了Eu掺杂使NdB6传导电子数量减少,从而导致其等离子共振频率能量的降低.采用第一性原理计算了NdB6和EuB6的能带结构、态密度、介电函数以及等离子共振频率能量,从而定性解释了Eu掺杂使NdB6透射光波长红移的特性.     

Electron transport through asymmetric DNA molecules

We investigate quantum mechanical electron transport along the long axis of the DNA molecule using an effective tight-binding model. The overall contour plot of transmission, the current-voltage characteristics, and the differential conductance are examined for the variation of backbone onsite energy, the energy-dependent hopping strength, and the contact coupling between the leads and the DNA molecule. It is shown that as backbone asymmetry increases, the merging and collapse of the two mini-bands take place and an extra resonance peak in the transmission appears. In addition, we present the modulation of voltage threshold in the current-voltage curves and a double-peak structure in the differential conductance due to the disappearance of the merged mini-band. Finally, in the Coulomb blockade regime of asymmetric contact coupling, a distinct and under-unity resonance in the transmission appears due to the interference effects between the DNA molecular bands and the electronic structure of the leads at the DNA-lead interface.     

亚波长分形结构太赫兹透射增强的机理研究

利用太赫兹时域光谱(terahertz time domain spectroscopy,简称THz-TDS),研究了亚波长金属分形结构在THz波段的透射增强特性.分别从实验和理论两个方面,研究了铜箔上各级分形结构THz透射增强现象的产生机理.结果表明,在低频区的透射增强主要是由低级分形线中电子运动的共振引起的,而高频区的透射增强则主要由高级分形线中电子运动的共振引起的.从而将这种透射增强效应归结为分形结构中电子的共振辐射,即分形结构的局域共振效应. 关键词： 分形 太赫兹 透射 共振峰     

Electron transport through a quantum cavity

Electron transport through a quantum cavity coupled with two one-dimensional waveguides is studied using a generalized scattering matrix method. In a symmetric N-channel cavity model, we are able to obtain an exact solution that predicts the electron energies at which the transmission of electron waves become zero. We found that the zero of transmission is closely related to the longitudinal resonance through inter-channel scattering, in particular, to the resonance of the highest propagating mode inside the cavity. This model provides a simple way to calculate the electron transmission through a cavity which could be useful in quantum waveguide engineering.