Secondary electron emission in scanning Ga ion, He ion and electron microscopes

The secondary electron (SE) emission for Ga ion, He ion and electron impact have been calculated using Monte-Carlo simulations, in which the trajectories of all the collision partners (i.e., primary ions, recoiled target atoms, and excited electrons (electron cascade) along which SEs are excited) have been simulated. The SE yields for Ga ion impact show a gradual decrease with increasing Z₂ which is opposite to that found for electron impact. The main reasons for the decrease in SE yield for Ga are the decrease in number and energy of electrons excited by the primary ions and the decrease in contribution of the recoiled atoms to the SE yield with increasing Z₂. For electron impact, both primary electrons and backscattered electrons (BSEs) excite the SEs. The additional SE excitation created by the electron cascade by BSEs is enhanced for high-Z₂ metals especially at E > a few keV. For He ion impact, the Z₂-dependence is between that for the Ga ions and the electrons and is weak because the He ion is light but still much heavier than an electron. As to the lateral resolution, the electron excitations by trapped He ions dominate the SE yield, so that the SE excitation volume is narrower than for electron and Ga impacts. This small contribution of BS He ions to the SE yield does not increase the information depth determined by the trapped He ions, in contrast with the large contribution of BSEs to the SE yields for SEM imaging. The simulated incident-angle dependence in SE yields shows that the topography contrast for He-SIM imaging is clearer than that obtained by SEM and Ga-SIM imaging.     

Surface characteristics and electrical breakdown of alumina materials

The electrical breakdown of alumina materials is one of the difficulties in higher electric field applications. This breakdown takes place due to localized excess heating, which is induced by surface defects, multipactor, and surface discharge. These factors were evaluated for several commercial alumina ceramics using a scanning electron microscope and comparing these observations with high-power rf transmission tests. The results indicate that alumina ceramics without F-center defects and lower surface charging are feasible for higher electric field operation.     

基于扫描电子显微镜的二次电子发射系数测量

二次电子发射特性对许多领域的真空器件有着重要的影响,准确测量二次电子发射系数至关重要。本文介绍了一种基于扫描电子显微镜的二次电子发射系数的测量方法。利用扫描电子显微镜电子束流的高稳定性和电子能量的宽范围可调的特性,引入法拉第杯样品台,通过改变电子束扫描速度,放大倍数及聚焦状态等电镜参数,对平滑Ag的二次电子发射系数进行测量。结果显示,平滑Ag的二次电子发射系数不受电镜参数影响,且与参考文献测量结果相符合。本测试方法对于研究材料宽电子能量范围的二次电子发射特性具有重要的参考意义。     

Secondary electron emission of doped PZT ceramics

Secondary electrom emission yield () and the surface work function values () were measured for lead zirconium titanate (PZT) doped with lanthanum, strontium, and niobium. The single pulse method was used in LEED/Auger geometry for measuring the secondary electron emission yield while the retarding potential technique was employed for measuring the work function. In view of the application of ceramics as continuous dynodes in electron multipliers, the secondary electron emission and electical conductivity data is analysed for reduced PLZT ceramics. Maximum of 2.7 was found to remain unchanged after reduction of PLZT. Dionne's equation was used as a basis for analysis of secondary electron emission measurements to estimate escape depth and emission probability.     

Secondary electron emission characteristics of MgO-ZnO alloy thin film layer for AC PDP

In this study, we attempted to reduce firing voltage of ac-PDPs by alloying MgO electron emission material with ZnO. This approach was aimed to reduce band gap energy of MgO by the alloying and thereby promote the Auger neutralization reaction of Xe⁺ ions on MgO surface. Pellets were prepared by sintering MgO and ZnO powder mixture at 1300 °C for 8 h under nitrogen atmosphere. Test panels with such alloyed MgO films showed significantly reduced firing voltages, especially when the discharge gas is of high Xe content. These results represent a new way of approaching in the development of electron emission materials for ac-PDPs.     

Side electron emission device using a composite of carbon nanofibers and aluminum

A new side electron emission device (SEED) was fabricated with carbon nanofiber/aluminum (CNF/Al) composites prepared by the elastomer precursor method. In the SEED, a cross-sectional side face of the CNF/Al composite plate was perpendicularly placed onto an anode surface by inserting an insulating spacer. Above a certain threshold voltage in a vacuum, field electrons were obtained from the side face of the composite emitter. With increasing content of CNFs in the composite, the threshold voltage decreased and emission currents increased. The current of ~ 8 μA was kept stable up to 93 h under a continuous application of 1 kV. This improved stability as compared to a conventional field emission device was attributed to a reduced damage of CNFs in the SEED structure.     

Dependence of the channel electron multiplier noise spectral functions on the parameters of its operation

The channel electron multiplier (CEM) current flicker noise was examined for different parameters of its operation. In particular, the dependence of CEM power spectral density function on its output current value has been verified. Also the dependence of the CEM power spectral density function on the input electron energy was investigated.     

铁电阴极电子发射研究进展

铁电发射是一种新型强流受激电子发射，本文综述了铁电弱发射和强发射的研究现状及其发射机理，重点分析了不同的铁电体相结构、电压脉冲激励波形、铁电发射结构以及萃取电压的波形等对铁电阴极电子发射特性和工作机理的影响，总结了目前铁电阴极等离子体辅助电子发射机理和模型，最后介绍了铁电阴极的应用前景。     

石墨烯纳米片及其场发射性能研究

两维石墨烯纳米材料是目前材料研究的热点之一,其中石墨烯纳米片的一个重要特征是有一条一维尖锐的刀口状边缘,电场增强系数大,是很好的电子场发射材料。本文介绍了石墨烯纳米片结构特点,综述了石墨烯纳米片的制备及电子发射性能,指出了目前研究存在的问题和研究方向。     

伴有二次电子发射的磁化等离子体鞘层结构特性

建立了包括电子、离子以及器壁发射二次电子的磁化等离子体鞘层流体模型,采用四阶龙格库塔法数值研究了伴有二次电子发射的磁鞘结构特性。模拟结果显示二次电子发射对于弱磁等离子体鞘层中的离子密度影响较大,而对于磁场较强的等离子体鞘层,鞘层中离子密度分布主要由磁场来决定。磁场的存在可以促进器壁电子的发射,磁场的增加或二次电子发射系数的增加都将使得鞘层厚度的减小,同时将导致沉积到器壁的离子动能流发生变化,从而直接影响器壁材料的性能。     

低能原电子下形状因子对金属曲面二次发射系数的影响

提出金属曲面二次电子发射的形状因子概念,并从理论上论述了形状因子对曲面二次电子发射系数的影响。从半经验理论出发,推导出低能原电子入射下,金属曲面二次发射系数与入射角的近似关系,并结合曲面形状,得到形状因子一般表达式,进而求出金属曲面的二次发射系数。以圆柱曲面为例,计算其形状因子和低能入射下其二次发射系数,并用实验数据证明了该理论的正确性,最后对结果进行了讨论,得到如下结论:在低能原电子入射情况下,金属曲面二次发射系数为金属材料二次发射系数与形状因子相乘所得。     

A study on the secondary electron emission from Na-ion-doped MgO films in relation to the discharge characteristics of plasma display panels

Using a sol-gel precursor, Na-ion-doped MgO was prepared and applied to alternative current plasma display panels (ac-PDP). The cathodoluminescence spectra showed that the F⁺ center was increased as the concentration of Na⁺ was increased. Numerous pores were found on the printed MgO surface and seemed to give higher memory margin of ac-PDP compared to an electron beam-evaporated MgO film. All doped MgO showed higher secondary electron emission than printed pure MgO, likely owing to the O defect states of MgO. In addition, this result indicated the operational memory margin of the ac-PDP was directly proportional to the grade of surface charging.     

C基薄膜电子场发射的一般特性及发射模型

介绍了几种碳基材料的场发射特性及其发射模型.金刚石表面具有较低的或负的电子亲和势,因无法实现N型掺杂,难以用作电子发射材料.类金刚石膜及非晶碳膜材料经过"激活"后在表面形成具有较大场增强因子的熔坑,在几～几十V/μm的低阈值电场下得到非本征的电子发射,纳米结构的碳和碳纳米管本身具有较大的场增强因子,是较有前途的平面阴极场发射材料.碳基材料的导电性不同,遵循的发射模型不同.     

Effect of radiation damage on ion-induced electron emission from highly oriented pyrolytic graphite

The dependences of ion-electron emission yields γ for highly oriented pyrolytic graphite (HOPG) under 30 keV N₂⁺ ion irradiation on target temperature at different ion incidence angles (0-80°) have been measured. The fluences were 10¹⁸-10¹⁹ ion/cm² and irradiation temperatures were varied from room temperature to 400 °C. At normal ion incidence a step-like increase of yield, analogous to the γ-behaviour for polygranular graphites, has been found at an annealing temperature T_a. This effect and the changes of γ(T) with ion incidence angle are discussed in terms of the change of electron path length and the transparency of the lattice for ion beams with increasing degree of lattice order.     

Enhanced electron emission from titanium coated multiwalled carbon nanotubes

Enhanced field emission properties and improved crystallinity of titanium (Ti) coated multiwalled carbon nanotubes (MWCNTs), prepared by microwave plasma enhanced chemical vapour deposition have been observed. Ti films of extremely low thicknesses (0.5 nm, 1.0 nm and 1.5 nm) were coated over carbon nanotubes (CNTs) and their field emission behaviour was investigated. The turn on field of Ti coated CNTs was found to be low (~ 0.8 V/μm) as compared to pristine CNTs (~ 1.8 V/μm). The field enhancement factor for Ti coated CNTs was quite large (~ 1.14 × 10⁴) as compared to pristine CNTs (~ 6 × 10³). This enhancement in electron emission is attributed to the passivation of defects and improved crystallinity of CNTs. Surface morphological and microstructural studies were carried out to investigate the growth of pristine and Ti coated CNTs. It was observed that Ti nanoclusters adsorb on the edges of MWCNTs and increase their crystallinity. This increase is directly correlated with the thickness of Ti film deposited. Micro Raman spectroscopy confirmed the improved crystallanity of Ti coated CNTs.     

The effect of crystalline structure on molecular effect in ion-induced electron emission

The results of experimental and theoretical study of the molecular effect in ion-induced electron emission from single crystal and polycrystalline materials are presented. It has been found that the electron emission yield γ₂ under N₂⁺ bombardment of a single crystal shows a dependence on ion incidence angle θ, which is analogous to the anisotropy of the yield γ₁ under N⁺ impact. The ratio R₂(θ)=γ₂/2γ₁<1 exhibits, for single crystals, a drastic angular dependence, which was successfully described on the basis of electron sweeping-out mechanism by conjunction of both the sharp channeling at θ<ψ_L and the shadowing-caused bell-like pattern at θ>ψ_L, the Lindhard angle.     

Effects of surface track potential on secondary electron emission and surface stopping power

In ion-surface scattering a positive surface track potential is induced on the surface behind the projectile due to ionizing collisions. The surface track potential is expected to affect secondary electron emission as well as the energy loss process of the projectile ions. We measure secondary electron yield induced by 0.5 MeV/u H⁺, He²⁺, Li²⁺ and B³⁺ ions during grazing angle scattering at a KCl(0 0 1) surface. The position-dependent secondary electron production rate was derived from the observed secondary electron yield. The secondary electron production rate is normalized by the mean square charge of the reflected ions. The normalized rate decreases with Z₁ suggesting that the surface track potential recapture the secondary electrons. We also measure the energy losses of 0.5 MeV/u H⁺, He²⁺, Li²⁺, B³⁺ and C⁴⁺ ions during grazing angle scattering at a KCl(0 0 1) surface. The observed result suggests that the surface stopping power is reduced by the surface track potential.     

第一性原理研究PDP放电单元MgO保护层各种空缺对二次电子发射系数的影响

基于密度泛函理论的第一原理赝势法,研究了PDP放电单元中MgO保护层在形成氧空缺后的电子结构的变化.通过对能带结构和态密度分布的计算,可以看到MgO形成氧空缺后在禁带中引入了能级.本文计算了完整MgO以及含F、F~+、F~(2+)空缺的MgO晶体,得到不同能带结构和态密度分布,同时计算了相应的二次电子发射系数.结果表明空缺的形成,可有效提高二次电子发射系数,其中形成F空缺的MgO晶体的二次电子发射系数最大.     

工艺参数对Ar~+改性无氧铜表面形貌及二次电子发射的影响

为了降低材料的二次电子发射系数,本文对高导电无氧铜(OFHC,简称无氧铜)进行离子束表面改性处理,并研究其最优工艺条件,重点考查了温度、时间等工艺参数对表面形貌以及二次电子发射系数(δ)的影响。利用扫描电镜、能谱仪等对表面形貌及成分进行分析并在此基础上对改性后样品的表面形貌形成机理进行了初步探讨。实验得出最佳工艺为:在600℃下离子束改性处理1 h。该参数下处理的无氧铜样品的二次电子发射系数降低63.5%。     

电子辐照介质材料二次电子发射系数与能谱测量数据库

电子辐照电介质材料的二次电子发射特性是影响各类真空电子器件与设备性能的重要参数,本文对电子束辐照下二十余种常用的典型介质材料的二次电子发射特性进行了实验测量研究.采用收集极负偏压法测量二次电子发射系数(SEY),通过给二次电子收集极加载不同的偏压来引导二次电子的运动,实现对积累电荷的中和,实验获得了介质材料的SEY随着...