电子回流对相对论速调管稳定工作的影响

模拟研究了电子束电压、电流及注入微波功率等参数对相对论速调管放大器中电子回流产生的影响,模拟发现注入微波过高、电子束电压过低及电子束电流过大都会导致电子回流。同时研究了回流电子对相对论速调管稳定工作的影响,研究发现,电子的回流会引起自激振荡,进而导致锁频锁相失败,器件不能稳定工作。     

A New Scheme for High‐Intensity Laser‐Driven Electron Acceleration in a Plasma

We propose a new approach to high‐intensity relativistic laser‐driven electron acceleration in a plasma. Here, we demonstrate that a plasma wave generated by a stimulated forward‐scattering of an incident laser pulse can be in the longest acceleration phase with injected relativistic beam electrons. This is why the plasma wave has the maximum amplification coefficient which is determined by the acceleration time and the breakdown (overturn) electric field in which the acceleration of the injected beam electrons occurs. We must note that for the longest acceleration phase the relativity of the injected beam electrons plays a crucial role in our scheme. We estimate qualitatively the acceleration parameters of relativistic electrons in the field of a plasma wave generated at the stimulated forward‐scattering of a high‐intensity laser pulse in a plasma. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magneto-optical studies of ballistic electron transport in single barrier heterostructures

We report an investigation of ballistic electron transport in GaAs/AlGaAs p-i-n single barrier structures with magnetic fields of up to 14T applied parallel to the tunneling direction (B//z). The energy distribution and relaxation processes of the non-equilibrium electron population injected into the p-doped collector from the Landau levels of the emitter accumulation layer are studied by means of electroluminescence (EL) spectroscopy. The observation of emitter Landau level structure in the ballistic electron EL spectra shows that the 2D to 3D tunneling process is elastic. In addition to the ballistic electron EL, cross-barrier recombination between the electron and hole accumulation layers is observed. This allows a precise determination of the initial energy distribution of the injected electrons.     

The role of multielectrode geometry in the generation of pulsedintense electron beams in preionization-controlled open-endedhollow-cathode transient discharges

High-voltage hollow-cathode glow discharges are used more and more to generate intense, pulsed electron beams. Such intense electron beams can be produced with high efficiency in preionization-controlled open-ended hollow-cathode transient discharges (PCOHC). This novel discharge is initiated by a low-current dc preionization discharge. The beam parameters are similar to those of the electron beam generated in pseudospark discharges. In this work, we present some measurements of the parameters for the electron beam generated by using a multielectrode (multigap) system instead of the single-gap device in this PCOHC configuration. This kind of multielectrode device was already used in pseudosparks to improve the intensity and collimation of the extracted beam. By using the multigap instead of the single gap, the total beam current (100-120 A) and the energetic part of the beam current (peak current 60-90 A and electron energies higher than approximately 3 keV) were substantially increased. However, the energy spectrum of the fast component has a large fraction of electrons at lower energies (4-10 keV for 26 kV breakdown voltage) when a multigap device is used instead of the single-gap configuration. A comparison between the single-gap and multigap PCOHC-produced pulsed intense electron beam is made too. The differences between the high-power pulsed electron beams produced in single-gap and multigap PCOHC configurations seem to be due to different developments of beam generation phases     

Drag of ballistic electrons by an ion beam

Drag of electrons of a one-dimensional ballistic nanowire by a nearby one-dimensional beam of ions is considered. We assume that the ion beam is represented by an ensemble of heavy ions of the same velocity V. The ratio of the drag current to the primary current carried by the ion beam is calculated. The drag current turns out to be a nonmonotonic function of velocity V. It has a sharp maximum for V near v _nF/2, where n is the number of the uppermost electron miniband (channel) taking part in conduction and v _nF is the corresponding Fermi velocity. This means that the phenomenon of ion beam drag can be used for investigation of the electron spectra of ballistic nanostructures. We note that whereas observation of the Coulomb drag between two parallel quantum wires may in general be complicated by phenomena such as tunneling and phonon drag, the Coulomb drag of electrons of a one-dimensional ballistic nanowire by an ion beam is free of such spurious effects.     

新型金属丝靶电子源实验研究

电子束在基础科学研究、工农业生产和医疗领域发挥了重要作用。提出了一种新型的电子源技术方案:高功率激光脉冲轰击金属丝靶,可以产生大量能量在百keV量级的热电子,一部分热电子在丝靶表面自生电磁场的作用下沿着丝靶运动,丝靶后方可以获得指向性良好的电子束。实验上成功在金、钨和铜丝靶后方获得了电子束团,测量了束团束斑、电荷量和能谱。铜丝靶单发实验收集到的电子束团总电荷量可达3 nC,能量分布在0～240 keV区间内,能谱在100 keV附近呈现峰值。提出了微波压缩方案,设计了2腔微波聚束腔,利用ASTRA对微波腔压缩过程进行了模拟计算。结果显示,可以将电荷量1 nC、长度55 ps的束团压缩至27 ps,满足后续微波加速器对电子源的要求。     

有机/无机复合双层电子传输层的量子点发光二极管

采用有机/无机复合双层电子传输层（ETL）研制绿色QLEDs,其中有机ETL采用OLED中常见的ETL材料,无机ETL采用ZnO纳米颗粒,并通过调控有机ETL厚度改变电子注入,使电子/空穴达到平衡。制备的器件结构为:ITO/PEDOT:PSS/TFB/QDs/ZnO NPs/TPBI:Liq/Al,其中有机电子传输层TPBI:Liq采用真空蒸镀沉积。与仅采用ZnO电子传输层的器件相比,可以使器件性能得到大幅提升:器件的最大电流效率从11.53 cd/A提升到22.77 cd/A,同时器件的启亮电压、电致发光光谱无明显变化。判断有机ETL的主要作用是抑制了过量电子的注入和传输,在发光亮度变化不大的情况下,降低了器件的无效复合（例如俄歇复合）电流,从而使电流效率明显提升。     

SUPPRESSION OF BALLISTIC ELECTRON TRANSMISSION THROUGH A SEMICONDUCTOR Π-STRUCTURE BY AN EXTERNAL TRANSVERSE ELECTRIC FIELD

We have conducted numerical studies of ballistic electron transport in a semicon-ductor II-structure when an external transverse electric field is applied. The device conductance as a function of electron energy and the strength of the transverse electric field is calculated on the basis of tight-binding Green's function formalism. The calculations show that a relatively weak electric field can induce very large decrease in the electron transmission across the structure. When the transverse electric field is sufficiently strong, electrons can hardly be transported through the device. Thus the performance of the device can be greatly improved for it is much easier to control electron transport through the device with an external transverse electric field.     

SUPPRESSION OF BALLISTIC ELECTRON TRANSMISSION THROUGH A SEMICONDUCTOR Π-STRUCTURE BY AN EXTERNAL TRANSVERSE ELECTRIC FIELD

We have conducted numerical studies of ballistic electron transport in a semicon-ductor II-structure when an external transverse electric field is applied. The device conductance as a function of electron energy and the strength of the transverse electric field is calculated on the basis of tight-binding Green's function formalism. The calculations show that a relatively weak electric field can induce very large decrease in the electron transmission across the structure. When the transverse electric field is sufficiently strong, electrons can hardly be transported through the device. Thus the performance of the device can be greatly improved for it is much easier to control electron transport through the device with an external transverse electric field.     

Diffusion of hydrogen in Pd assisted by inelastic ballistic hot electrons

Sykes et al. [Proc. Natl. Acad. Sci. U.S.A. 102, 17907 (2005)] have reported how electrons injected from a scanning tunneling microscope modify the diffusion rates of H buried beneath Pd(111). A key point in that experiment is the symmetry between positive and negative voltages for H extraction, which is difficult to explain in view of the large asymmetry in Pd between the electron and hole densities of states. Combining concepts from the theory of ballistic electron microscopy and electron-phonon scattering we show that H diffusion is driven by the s-band electrons only, which explains the observed symmetry.     

On the production of flat electron bunches for laser wakefield acceleration

We suggest a novel method for the injection of electrons into the acceleration phase of particle accelerators, producing low-emittance beams appropriate even for the demanding high-energy linear collider specifications. We discuss the injection mechanism into the acceleration phase of the wakefield in a plasma behind a high-intensity laser pulse, which takes advantage of the laser polarization and focusing. The scheme uses the structurally stable regime of transverse wakewave breaking, when the electron trajectory self-intersection leads to the formation of a flat electron bunch. As shown in three-dimensional particle-in-cell simulations of the interaction of a laser pulse elongated in the transverse direction with an underdense plasma, the electrons injected via the transverse wakewave breaking and accelerated by the wakewave perform betatron oscillations with different amplitudes and frequencies along the two transverse coordinates. The polarization and focusing geometry lead to a way to produce relativistic electron bunches with an asymmetric emittance (flat beam). An approach for generating flat laser-accelerated ion beams is briefly discussed. The text was submitted by the authors in English.     

Light-emitting field-effect transistor based on a tetracene thin film

We report the first organic light-emitting field-effect transistor. The device structure comprises interdigitated gold source and drain electrodes on a Si/SiO(2) substrate. A polycrystalline tetracene thin film is vacuum sublimated on the substrate forming the active layer of the device. Both holes and electrons are injected from the gold contacts into this layer leading to electroluminescence from the tetracene. The output characteristics, transfer characteristics, and the optical emission properties of the device are reported. A possible mechanism for electron injection is suggested.     

Mesoscopic spin-dependent reflection experiments on InSb- and InAs-based heterostructures

Spin–orbit interaction in two-dimensional electron systems can lead to a spin-dependent reflection of carriers off a lithographic barrier. Scattering of a spin-unpolarized beam from the barrier leads to the creation of two fully spin-polarized side beams in addition to an unpolarized specularly reflected beam. We experimentally demonstrate a method to create spin-polarized beams of ballistic electrons in mesoscopic samples fabricated on InSb/InAlSb and InAs/AlGaSb heterostructures. We describe two geometries, one open and one closed, in which the spin-dependent reflection and spin-dependent semiclassical trajectories were observed.     

Hydrodynamic effects in interacting Fermi electron jets

We theoretically study hydrodynamic phenomena originating from electron-electron collisions in a two-dimensional Fermi system. We demonstrate that an electron beam sweeping past an aperture creates a pumping effect, attracting carriers from this aperture. This pumping effect originates from the specific electric potential distribution induced by the injected electrons. In the regions near the main stream of injected electrons, a positive potential is induced by the injected electrons. Thus, the normally repulsive Coulomb interaction leads to an attractive force in the Fermi system. This quantum pumping mechanism in a Fermi system differs qualitatively from the Bernoulli pumping effect in classical liquids. We also discuss possible experimental realizations.     

Spin-dependent electron-proton scattering in the Delta-excitation region

We report on measurements of the cross section and provide first data on spin correlation parameters A(TT') and A(TL') in inclusive scattering of longitudinally polarized electrons from nuclear-polarized hydrogen. Polarized electrons were injected into an electron storage ring operated at a beam energy of 720 MeV. Polarized hydrogen was produced by an atomic beam source and injected into an open-ended cylindrical cell, located in the electron storage ring. The four-momentum transfer squared ranged from Q2 = 0.2 GeV(2)/c(2) at the elastic scattering peak to Q2 = 0.11 GeV(2)/c(2) at the Delta(1232) resonance. The data provide a stringent test of pion electroproduction models.     

基于紧聚焦超高斯激光脉冲的大电量低发散度电子束产生

在激光尾场加速中,光学注入是一种有效的可控电子注入机制。然而,低电量、大发散度的电子束特性无法满足实际应用的需要。为获得大电量、高品质电子束提出采用紧聚焦的超高斯激光作为注入脉冲的新型注入方案。研究发现,相比于普通高斯激光,紧聚焦的超高斯激光不仅能够将电子束发散度降低近一个数量级,而且能够保持电子束电荷量不变。通过哈密顿理论模型证实,离轴电子是发散度的主要来源,而紧聚焦的超高斯激光极大地限制了离轴电子的注入,因此有效地降低了电子束的发散度。     

一种用于偏扫电流校正的特征点参数采集装置

电子束快速成型设备偏扫系统工作频率高,磁偏扫装置的铁损、涡流等损耗导致偏扫轨迹产生偏差。通过获取偏扫区域内特征点基准偏扫参数并由插补算法计算区域内任意一点偏扫参数,能够较好地抑制动态偏差;但由光学观察系统判断电子束斑点位置所获得的基准偏扫参数精确性较低。为提高偏扫轨迹精度,在现有电子束快速成型机上加装一种特征点参数采集装置,收集产生的二次反射电子,通过二次反射电子信号判断特征点通孔中心与电子束斑点中心的对中性。实验表明:当电子束斑点位于特征点中心且聚焦于上表面时,二次反射电子信号最小,此时获得的基准偏扫参数精确性高,能够提高电子束偏扫加工的精度。     

An extended interaction oscillator based on a complex resonatorstructure

We report experimental investigation of a novel scheme for efficient interaction between a linear electron beam and an electromagnetic wave in a complex extended interaction structure. The structure of interest consists of a high R/Q, five-gap, coupled-cavity resonator that incorporates a coaxial section of a quarter plasma wavelength placed between the first and second cavities. In the coaxial section, beam and wave propagate in separate channels. The first cavity, strongly coupled to the other cavities through the wave channel of the coaxial section, serves as a buncher cavity. An inner channel running through the center conductor of the coaxial section provides a cutoff drift space for ballistic bunching of electrons, an effect that is shown to significantly enhance the interaction efficiency. Oscillation power of 2.2 kW at 16.6 GHz was demonstrated with an interaction efficiency of 30%. The total efficiency was further increased to 41% by incorporation of a two-stage depressed collector     

Flux-limited nonequilibrium electron energy transport in warm dense gold

An abrupt change in energy transport has been observed in femtosecond laser heated gold when the absorbed laser flux exceeds ~7×10(12) W/cm(2). Below this value, the absorbed flux is carried by ballistic motion of nonthermal electrons produced in interband excitation. Above this value energy transport appears to include ballistic transport by nonthermal electrons and heat diffusion by thermalized hot electrons. The ballistic component is limited to a flux of ~7×10(12) W/cm(2). This offers a unique benchmark for comparison with theory on nonequilibrium electron transport.