绝缘体二次电子发射系数测量装置的研制

 成功研制了测量绝缘体二次电子发射系数的测量装置，该装置主要由栅控电子枪系统、真空系统和电子采集系统组成，测量装置产生的原电子流的能量范围为0.8~60 keV。采用单脉冲电子枪法，测量了原电子能量范围为0.8~45 keV的多晶MgO的二次电子发射系数。测量中，收集极(偏置盒)离材料表面设置为约35 mm，偏置电压设置为 45 V。测量得到：用磁控溅射法制备的MgO的二次电子发射系数最大值约为2.83，处于 2~26范围内，其对应的原电子能量约为980 eV。这表明该装置测量的绝缘体二次电子发射系数是可信的，但用磁控溅射法制备的MgO的二次电子发射系数较低，这可能是制备MgO时引入了过多的杂质在MgO二次电子发射体里面所引起的。     

Secondary electron emission yield from vertical graphene nanosheets by helicon plasma deposition

The secondary electron emission yields of materials depend on the geometries of their surface structures.In this paper,a method of depositing vertical graphene nanosheet(VGN)on the surface of the material is proposed,and the secondary electron emission(SEE)characteristics for the VGN structure are studied.The COMSOL simulation and the scanning electron microscope(SEM)image analysis are carried out to study the secondary electron yield(SEY).The effect of aspect ratio and packing density of VGN on SEY under normal incident condition are studied.The results show that the VGN structure has a good effect on suppressing SEE.     

毫米波速调管电子光学系统的研究

电子光学系统是毫米波速调管长寿命和整管性能实现的关键,毫米波速调管零件尺寸较小,为了在Ka波段和W波段实现千瓦量级的输出功率,要求具有高的电子注通过率及低的阴极负荷。对Ka波段和W波段电子光学系统特性进行了分析,确定了Ka波段10 kW分布作用速调管和W波段1 kW分布作用速调管电子光学系统的设计方案,利用软件对电子枪和聚焦系统的结构进行计算,并采用CST仿真软件对设计的电子枪发射的电子注在聚焦磁场中的状态进行优化。设计出的Ka波段速调管电子光学系统,电子枪工作电压26 kV,发射电流2 A,互作用区长度30 mm,磁场强度大于0.6 T,流通达到100%。设计的W波段速调管电子光学系统,电子枪工作电压17 kV,电流0.65 A,互作用区长度20 mm,磁场大于0.9 T,流通达到100%。已制成Ka波段速调管和W波段速调管,设计的电子光学系统能够满足速调管工程化需求。     

电子光学教学实验的开发

介绍利用单踪示波器的阴极射线管,结合模拟软件,开展电子光学实验教学的教学内容设计和教学实践情况.电子光学实验教学的开展有利于学生掌握相关知识和研究方法,受到学生欢迎.     

高电流密度圆柱状电子光学系统设计

设计了高电流密度圆柱状电子枪,并分析了枪体参数对电子注品质的影响;运用径向力平衡理论计算了聚焦磁场.三维模拟软件CSTPARTICLESTUDIO模拟显示,在枪体电极和空间电荷形成的静电场,以及聚焦磁场作用下,电子呈角向先变速后匀速螺旋状运动,其旋转半径始终与出射阴极面时的半径相同,从而在枪区和互作用通道内维持了注包络水平.模拟结果与设计理论相符.注平均电流密度达到24·4A/cm2,层流性良好,填充因子76·7%,流通率100%.     

金属二次电子发射系数表达式

根据二次电子发射的主要物理过程,推导出二次电子发射系数和单位背散射电子产生的内二次电子数与原电子产生的内二次电子数之比、原电子入射能量、参数、最大二次电子发射系数、背散射系数之间的关系式。根据实验结果,给出了2~10 keV比率的表达式。根据推导的关系式,用实验数据分别计算出6种金属的平均参数。发现6种金属的平均参数都近似为一个常数11.89(eV)0.5。根据推导的关系式和计算的参数,推导出以背散射系数、原电子入射能量和最大二次电子发射系数为变量的二次电子发射系数通式。用该通式计算出二次电子发射系数,并与相应的实验值进行了比较,最后成功地推导出金属2~10 keV的二次电子发射系数通式。     

金属二次电子发射系数表达式

根据二次电子发射的主要物理过程,推导出二次电子发射系数和单位背散射电子产生的内二次电子数与原电子产生的内二次电子数之比、原电子入射能量、参数、最大二次电子发射系数、背散射系数之间的关系式。根据实验结果,给出了2~10 keV比率的表达式。根据推导的关系式,用实验数据分别计算出6种金属的平均参数。发现6种金属的平均参数都近似为一个常数11.89(eV)0.5。根据推导的关系式和计算的参数,推导出以背散射系数、原电子入射能量和最大二次电子发射系数为变量的二次电子发射系数通式。用该通式计算出二次电子发射系数,并与相应的实验值进行了比较,最后成功地推导出金属2~10 keV的二次电子发射系数通式。     

Influence of surface topography on the secondary electron yield of clean copper samples

Secondary electron yield (SEY) due to electron impact depends strongly on surface topography. The SEY of copper samples after Ar-ion bombardment is measured in situ in a multifunctional ultrahigh vacuum system. Increasing the ion energy or duration of ion bombardment can even enlarge the SEY, though it is relatively low under moderate bombardment intensity. The results obtained with scanning electron microscopy and atomic force microscopy images demonstrate that many valley structures of original sample surfaces can be smoothed due to ion bombardment, but more hill structures are generated with stronger bombardment intensity. With increasing the surface roughness in the observed range, the maximum SEY decreases from 1.2 to 1.07 at a surface characterized by valleys, while it again increases to 1.33 at a surface spread with hills. This phenomenon indicates that hill and valley structures are respectively effective in increasing and decreasing the SEY. These obtained results thus provide a comprehensive insight into the surface topography influence on the secondary electron emission characteristics in scanning electron microscopy.     

Secondary electron yield enhancement by MgO capping layers

The yield of secondary electrons emitted from an epitaxial three monolayer (3 ML) NiO(1 0 0)/Ag(1 0 0) film excited by soft X-ray linearly polarized synchrotron radiation at the Ni L_2,3 absorption threshold has been measured for different values of the thickness of a MgO(1 0 0) capping layer. Compared with the as grown 3 ML NiO(1 0 0)/Ag(1 0 0) film, we observe a significant enhancement by about a factor 1.2 of the secondary electron emission for the capped 8 ML MgO(1 0 0)/3 ML NiO(1 0 0)/Ag(1 0 0) sample. A further substantial yield enhancement by a factor 1.6 with respect to the uncapped NiO sample is observed after deposition of an additional 8 ML MgO(1 0 0) film, for a total capping layer thickness of 16 ML. The observed secondary electron yield enhancement is discussed in terms of modified electronic structure, surface work function changes, and characteristic electron propagation lengths.     

Refractive index and material dispersion in relativistic electron optics

The refractive index and material dispersion associated with relativistic motion of electrons are calculated. Moreover, the wavelength dependence of refractive index is compared with the Sellmeier model for the index of refraction of lightwaves.     

电子入射角度对聚酰亚胺二次电子发射系数的影响

采用具有负偏压收集极的二次电子发射系数测试系统, 对聚酰亚胺样品的二次电子发射系数与入射电子角度和入射电子能量的关系进行了测量. 测量结果表明, 在电子小角度入射样品的情况下, 随着入射角度的增加, 二次电子发射系数单调增加, 并符合传统的规律, 但是在电子大角度入射时, 却与此不符合. 测量显示, 出现偏差时对应的临界电子入射角度随着入射电子能量的降低而减小. 采用简化的电子弹性散射过程和卢瑟福弹性散射截面公式对这种偏差的出现进行了分析, 并推导出修正后的二次电子发射系数的计算公式. 修正后的二次电子发射系数的计算结果更加符合实验结果.     

Secondary electron emission of sputtered alumina films

Secondary electron emission yieldδ was measured for thin films of alumina prepared byrf sputtering technique. Single pulse method was used along with 4-gridleed optics system to determineδ. Maximum value of 4·3 was obtained at primary energy of 350 eV. The Dionne’s theory was used to analyse the results and the emission probability escape depth and absorption coefficient of secondaries were also estimated. Fairly good correlation is observed between experimental and theoretical values ofδ for beam energies upto 1 keV.     

Electron optics for high throughput low energy electron microscopy

Novel electron-optical components and concepts aiming at improving the throughput and extending the applications of a low energy electron microscope (LEEM) have been developed. An immersion magnetic objective lens can substantially reduce e-e interactions and the associated blur, as electrons do not form a sharp crossover in the back-focal plane. The resulting limited field of view of the immersion objective lens in mirror mode can be eliminated by immersing the cathode of the electron gun in a magnetic field. A dual illumination beam approach is used to mitigate the charging effects when the LEEM is used to image insulating surfaces. The negative charging effect, created by a partially absorbed mirror beam, is compensated by the positive charging effect of the secondary beam with an electron yield exceeding 1. On substrates illuminated with a tilted beam near glancing incidence, large shadows are formed on even the smallest topographic features, easing their detection. On magnetic substrates, the magnetic flux leaking above the surface can be detected with tilted illumination and used to image domain walls with high contrast.     

Wiggler聚焦带状注速调管电子光学系统的设计

带状注速调管可以在高频段实现高功率微波输出,电子光学系统是带状注速调管的关键部件。阐述了Wiggler双平面聚焦理论,设计了新型椭圆形柱面阴极和椭圆形聚焦极结构,阴极曲率半径为17 mm,长轴10 mm,短轴4 mm;聚焦极长轴28.8 mm,短轴10.4 mm。采用这种结构可以直接产生椭圆形带状电子注,且阴极发射电流密度较为均匀。设计了周期长度为8 mm,总长度为108 mm,中间带有凹槽并可以实现双平面聚焦的Wiggler结构,模拟显示电子注填充因子在75%左右,通过率达到100%。设计了新型的菱形收集极结构,电子轨迹在收集极内发散均匀。     

Paraxial imaging electron optics and its spatial-temporal aberrations for a bi-electrode concentric spherical system with electrostatic focusing

The paraxial solutions play an important role in studying electron optical imaging system and its spatial-temporal aberrations, as was discussed in previous paper [1], but investigation of a bi-electrode concentric spherical system with electrostatic focusing directly from paraxial electron ray equation and paraxial electron motion equation has not been done before. In this paper, we shall use the paraxial equations to study the spatial-temporal trajectories and their aberrations for a bi-electrode concentric spherical system with electrostatic focusing.In the present paper, start from the paraxial ray equation and paraxial motion equation, the paraxial spatial-temporal trajectory of moving electron emitted from the photocathode has been solved for a bi-electrode concentric spherical system with electrostatic focusing. The paraxial static and dynamic electron optics, as well as the paraxial spatial-temporal aberrations in this system are then discussed, the general regularity of imaging in paraxial optical system has been explored. The paraxial spatial aberrations, as well as the paraxial temporal aberrations with different orders, have been defined and deduced, that are classified by the order of (?_z/?_ac)^1/2 and (?_T/?_ac)^1/2. Thus we get same conclusions about paraxial spatial and temporal aberrations as we have given in the previous paper and it completely shows that the paraxial spatial-temporal aberrations can be investigated directly from the paraxial ray equation and paraxial motion equation.     

Effect of Cu doping on the secondary electron yield of carbon films on Ag-plated aluminum alloy

Reducing the secondary electron yield (SEY) of Ag-plated aluminum alloy is important for high-power microwave components. In this work, Cu doped carbon films are prepared and the secondary electron emission characteristics are studied systematically. The secondary electron coefficient δ_max of carbon films increases with the Cu contents increasing at first, and then decreases to 1.53 at a high doping ratio of 0.645. From the viewpoint of surface structure, the higher the content of Cu is, the rougher the surface is, since more cluster particles appear on the surface due to the small solid solubility of Cu in the amorphous carbon network. However, from viewpoint of the electronic structure, the reduction of the sp² hybrid bonds will increase the SEY effect as the content of Cu increases, due to the decreasing probability of collision with free electrons. Thus, the two mechanisms would compete and coexist to affect the SEY characteristics in Cu doped carbon films.     

分层校正自适应光学等晕区计算

在回顾单层模型与多层模型的基础上,首次导出按适当准则分层的大气等晕角普适表达式,并将贝克先前的结果作为一种特例包括在内.     

Secondary electron emission data of cesiated oxygen free high conductivity copper

Because of its relevance for negative hydrogen ion sources, the change in secondary electron emission with the adsorption of Cs on Cu was studied. Properly prepared disks of oxygen free high conductivity (OFHC) copper yielded a maximum secondary electron emission δ_max=1.54±3%. The deposition of ≈0.5 monolayer of Cs resulted in δ_max=3.40±3%.     

绝缘体二次电子发射系数测量装置的研制

成功研制了测量绝缘体二次电子发射系数的测量装置,该装置主要由栅控电子枪系统、真空系统和电子采集系统组成,测量装置产生的原电子流的能量范围为0.8~60 keV。采用单脉冲电子枪法,测量了原电子能量范围为0.8~45 keV的多晶MgO的二次电子发射系数。测量中,收集极(偏置盒)离材料表面设置为约35 mm,偏置电压设置为 45 V。测量得到：用磁控溅射法制备的MgO的二次电子发射系数最大值约为2.83,处于 2~26范围内,其对应的原电子能量约为980 eV。这表明该装置测量的绝缘体二次电子发射系数是可信的,但用磁控溅射法制备的MgO的二次电子发射系数较低,这可能是制备MgO时引入了过多的杂质在MgO二次电子发射体里面所引起的。     

Total electron yield mode for XANES measurements in the energy region of 2.1-6.0 keV

The total electron yield (TEY)mode has been developed successfully for XANES measurements at Beamline 4B7A of BSRF (Beijing Synchrotron Radiation Facility).Its performance was studied by measuring sulphur K-edge XANES of three CdS samples (mixed with graphite powder as an electric conductor)with different concentration:75%,50% and 25%.The data are collected in TEY mode and fluorescence yield (FY)mode respectively for comparison.The results demonstrate that the TEY spectra of three samples agree well with each other after the background is subtracted and normalized.The measured XANES spectra by TEY mode without bias and with 100V bias are almost identical to one another,but the signal-to-noise ratio of spectra measured without bias is better than that with 100V bias.The consistency of the self-absorption corrected FY spectra and TEY spectra are within 10% for the three samples.