Field emission monotron for THz emission

Small-signal negative conductance of a field emission monotron was calculated, which was considerably higher than that of a thermionic monotron due to strong bunching of emitted electrons in a field emission. The amplification constant of 28dB/mm is achieved at THz wave region by applying the monotron to a distributed amplifier and is sufficient to overcome power loss in a transmission line. In addition, a wide band frequency tunable electromagnetic wave source may be developed at THz wave region by providing a low loss microstrip line resonator with field emission array due to the gate voltage dependent phase constant of the line.     

Energy-resolved analysis of ferroelectric electron emission from TGS using emission electron microscopy

Ferroelectric electron emission arises when the spontaneous polarization of a ferroelectric is switched due to the application of an electric field. In order to study the origin of emission and the related emission mechanism, space-resolved emission electron microscopy has been employed. The integral energy distribution of the emitted electrons from triglycine-sulfate surfaces has been investigated using a cylindrical sector analyzer and an imaging retarding field analyzer. Space-resolved emission photography and energy distribution measurements were obtained, revealing the effect of ferroelectric switching on the electric field distribution and hence on the emission process. Evidence of secondary electron emission from the metal electrodes has been found.     

Enhanced near-band-edge emission and field emission properties from plasma treated ZnO nanowires

Near-band-edge emission in photoluminescence of ZnO nanowires was found to be significantly improved after plasma treatment. The ratio of ultraviolet emission peak intensity before and after plasma treatment is as high as 3.5. Field emission properties were considerably enhanced after plasma treatment as well. Current emission density has been increased two orders of magnitude under the same electric field. Passivation of surface states and surface morphology change were found to be responsible for such an effective improvement. Our results suggest that the plasma treatment method is effective in enhancing both the near-band-edge emission in photoluminescence and field electron emission performance from ZnO nanowires.     

Low-voltage nonstationary electron emission from single-walled carbon nanotubes as exoelectron emission

Low-voltage nonstationary electron emission from single-walled carbon nanotubes after the passage of high autoemission current has been observed. This emission is assumed to be exoelectron emission associated with mechanical stresses and defects appearing in nanotubes due to electrostatic forces acting on nanotubes in a strong electric field.     

Two-photon conical emission

A two-photon resonantly enhanced four-wave mixing (FWM) process leading to the conical emission of two new frequency components has been observed in atomic sodium vapor. A dye laser tuned close to the 3s → 3d two-photon allowed transition produces broad-band emission near the frequencies of the 3d → 3p and 3p → 3s transitions. This radiation is emitted in the forward direction in the form of cones surrounding the transmitted laser beam. The dependence of the cone angle on the emission wavelength and atomic number density is in excellent agreement with the predictions of a model that ascribes the origin of the conical emission to a phase-matched four-wave mixing process.     

Cooperative cascade emission

An experimental and theoretical study has been performed on the generating process of a cascade emission in a sample three-level system where the ground and the highest excited levels have been initially brought into a coherent superposition state by two-proton excitation. Experimentally the forward and the backward emissions of the upper and the lower transitions of the cascade were observed in Li, and each of the emission lines showed a characteristic growth. In the theoretical analysis it is found that a dephasing in the prepared superposition state is required for the cascade emission as a coupled three level superradiance to grow. Using the concepts of delay time, threshold, lifetime, etc. of the cooperative cascade emission, the general behavior of the experimental results is explained.     

Visualization of field induced ferroelectric electron emission from TGS using emission electron microscopy

Field induced electron emission from triglycinesulfate (TGS) has been investigated using parallel imaging electron emission microscopy (EEM). The emission phenomenon has been induced by applying an ac electrical field up to 2 kV/mm to a single crystal of approximately 0.1 mm thickness. Emission patterns have been observed as a function of the applied field amplitude and of the crystal temperature. At voltages below the coercive field, no emission is visible. When approaching the Curie temperature, emission gradually disappears. This indicates an electron emission mechanism relying on the existence of a switchable ferroelectric phase. The information content of the images is discussed, an interpretation is given on the basis of existing theories. PACS 68.37.-d; 77; 77.80.Fm; 77.80.-e     

Light emission from carbon nanofilaments/nanotubes at field electron emission

The spatial distribution of light emission has been studied in planar field electron emitters with long and sparse carbon nanofilaments/nanotubes. The photographic recording of light emission of the emitting nanofilaments/nanotubes is shown to be efficient to determine the position of individual nanofilaments/ nanotubes in different emitter surface areas, as well as to highlight the nanofilaments/nanotube agglomerate distribution over the emitter surface, which mainly contributes to its emission.     

Bombardment-induced light emission

An inescapable consequence of the bombardment of a solid with atomic particles in the energy range above a few tens of electron volts is the emission of particles from the solid via sputtering. A fraction of the sputtered flux emerges from the solid surface in an electronically excited state, and gives rise to the emission of light in a volume outside the surface. In this article, the experimental observations on this bombardment-induced light emission are reviewed together with the analytical applications of the technique and the present status of the mechanism leading to the excitation.     

场致发射的温度效应对微波管爆炸电子发射的影响

为研究场致发射的温度效应对微波管中爆炸电子发射过程的影响,在对比分析低温条件下的场致发射电流密度Fowler-Nordheim（FN）和一般的电子发射电流密度积分公式的基础上,利用细长圆柱形微凸起模型,重点考虑焦耳加热和热传导两个因素,编程计算得到了微凸起内部的温度分布和不同位置处温度随时间的变化。结果表明:场致发射的温度效应是一个重要影响因素,考虑温度对场致发射的影响后,微凸起内部各点的温度随时间呈非线性增长,且增长速率越来越大;在微波电场强度较弱时,若不考虑场致发射的温度效应而直接用FN公式表示的电流密度代入计算,会使爆炸发射延迟时间变短;当微波电场很强时,温度效应对爆炸发射延迟时间的影响则较小。     

碳纳米管的变温场发射

考察了温度变化对沉积在钨丝针尖上的碳纳米管场发射的影响，发现碳纳米管场发射电流随温度升高而增大，场发射电流的稳定性基本没有变化. 多根碳纳米管的场发射特性随温度变化出现偏离Fowler-Nordheim理论的现象，这种现象可能来自碳纳米管的不均匀性.     

亚微米电子发射材料的合成及发射性能

介绍一种气-液相合成技术合成多元碳酸盐及其制备阴极的发射性能.实验表明：采用该方法合成碳酸盐结晶小,形貌呈细丝状,丝径小于1μm,这种亚微米丝状碳酸盐能明显提高氧化物阴极的发射性能.通过对阴极激活后阴极表面的SEM分析,初步讨论了亚微米碳酸盐的发射机理. 关键词： 亚微米碳酸盐 气-液相合成技术 氧化物阴极 发射性能     

Thermionic field emission of electrons from metals and explosive electron emission from micropoints

We suggest a general approach to considering the thermionic, field, and thermionic field emissions of electrons from metals. For this purpose, based on the standard model of free electrons in a metal, we suggest a numerical method for determining the transmission coefficient through the potential barrier at the metal-vacuum interface suitable for an arbitrary barrier. This method is free both from the approximations based on the saddle-point approximation and characteristic of the analytical models for thermionic emission and from the approximations for the tunneling coefficient through the potential barrier characteristic of the models for field emission. Based on numerical simulations, we determine the thermal effect of the emission and ascertain that a very sharp transition from surface cooling by electron emission to heating occurs at certain electric field and temperature. We explain the triggering mechanism of the explosive electron emission observed during micropoint explosions by this phenomenon. The explosive emission is shown to begin when the level of the potential barrier at the micropoint tip drops below the Fermi level in the metal.     

反铁电陶瓷的强电子发射特性研究

采用掺镧锆锡钛酸铅反铁电陶瓷作为阴极材料,研究了脉冲电压激励下陶瓷的电子发射特性.当激励电压为800V、抽取电压为0V时,得到1.27A/cm²的发射电流密度;当抽取电压增加到4kV时,获得1700A/cm²的发射电流密度.分析了发射电流随抽取电压的变化关系,讨论了反铁电陶瓷强电子发射的内在机理.结果表明：掺镧锆锡钛酸铅反铁电陶瓷能够在较低的激励电压(400V)下实现电子发射,发射电流远大于按照Child-Langmuir定律计算出的电流,三接点附近局域反铁电—铁电相变产生初始电子发射,初始电子电离中性粒子形成等离子体,增强了电子发射. 关键词： 铁电阴极 反铁电体 电子发射     

Enhanced photon emission by field emission resonances and local surface plasmon in tunneling junction

We investigated the photon emission spectra on Ag (111) surface excited by tunneling electrons using a low temperature scanning tunneling microscope in ultrahigh vacuum. Characteristic plasmon modes were illustrated as a function of the bias voltage. The one electron excitation process was revealed by the linear relationship between the luminescence intensity and the tunneling current. Luminescence enhancement is observed in the tunneling regime for the relatively high bias voltages, as well as at the field emission resonance with bias voltage increased up to 9 V. Presence of a silver (Ag) nanoparticle in the tunneling junction results in an abnormally strong photon emission at the high field emission resonances, which is explained by the further enhancement due to coupling between the localized surface plasmon and the vacuum. The results are of potential value for applications where ultimate enhancement of photon emission is desired.     

Upshifted electron cyclotron emission

The possibility of inferring the high energy part of the electron distribution function by means of its electron cyclotron emission is investigated. It is shown, with different set-ups, that the emission leaving the plasma perpendicular to the magnetic field cannot achieve this goal. A new configuration viewing the plasma from the low field side, oblique respect to the magnetic field -upshifted emission — is presented and its useful properties for localizing the electrons, responsible for the emission, in real and momentum space discussed.     

氧化锌纳米棒场发射性能研究

采用简单物理气相沉积法制备出取向和非取向的氧化锌纳米棒，他们的场致电子发射性能测量结果表明，ZnO纳米棒具有较好的场发射性能，但是高度取向的ZnO纳米棒阵列并不利于获得高的场致电子发射电流密度.这可能是由于高密度ZnO纳米棒之间具有较高的屏蔽效应，降低了ZnO纳米棒阵列的场放大因子，从而影响了其场发射性能.相反，非取向ZnO纳米棒由于相互之间的屏蔽效应比较弱，而且表面存在容易成为发射中心的微小突起，表现出较好的场发射效果.这些结果不仅有助于加深我们对准一维纳米材料场致电子发射性能的理解，也为未来场发射电子器件的实际应用提供了可靠的依据. 关键词： 氧化锌 场发射 非取向     

Thermal field emission and thermal photofield emission from tungsten (110)

The total energy distibution in field emission from the (110) surface of tungsten has been measured at temperatures in the range from 300 to 1400 K, which are sufficiently high to cause significant emission from thermally populated electronic states. Above the Fermi level, a striking departure from the prediction of free electron theory is observed. A similar anomaly is observed in the total energy distribution in photofield emission from thermally populated initial states on tungsten (110). In s-polarized light at normal incidence the anomaly vanishes when the polarization vector is parallel to the [001] direction. The anomalous behaviour is attributed to emission from the p-like energy band that is responsible for the ellipsoidal sheet of the Fermi surface centred at the symmetry point N. A comparison between the enhancement factors measured in sand p-polarized light yields no evidence for surface resonances close to the upper limit of the p-like energy band.     

Anomalous thermal field emission

The field emissivity of ZrO₂/W(100) nanoheterostructures made by applying a thin (≈10 nm) ZrO₂ layer on the surface of a needle-like W(100) microcrystal is studied. At a nanoheterostructure temperature of ≈2000 K, electron emission is found to start at a low extracting (Laplace) field (below 50 V/μm). Under the conditions of steady electron emission, the emission current density from the surface of the heterostructure may reach anomalously high values (～10⁸ A/cm²). A phenomenological model of anomalous thermal field emission of electrons from the surface of the conductor (metal)-thin insulator heterostructure is suggested.