在线同位素分离器束流光学特性研究

在线同位素分离器系统是用于研究远离β稳定线的短寿命核素的有效工具.本文主要对ISOLDE型(55o)在线分离器的束流光学系统作了详细介绍,通过分析影响磁铁质量分辨本领的因素,指出把单透镜和四极透镜组合在一起使用可达到既提高分辨本领又不损失束流的要求.此外,根据CARR-ISOL的磁铁参数计算了不同影响因素下磁铁质量分辨本领及束斑水平宽度,发现在电源稳定度越高,加速电压越高,离子源归一化发射度越小时,磁铁的质量分辨率越高.     

金属钨热发射电子能量分布随温度的变化,

要提高电子显微镜的分辨率就必须减少像差,其中最主要的是球差和色差,球差早已有人提出用六极透镜系统来消除,并取得了一些成果。引起色差的原因有:电子枪加速电压的波动,透镜电流的波动及阴极发射出来的热电子具有能量分散度。所以,研究不同温度下阴极热发射电子的能谱曲线是很有意义的。作者利用金属钨W和拒斥场法。测量了不同温度下,W的电子能量分布(峰值和半宽度)随温度的变化。要得到电子束的能谱曲线,须先测出电子束的积分曲线,再对该曲线微分即得能谱曲线。实验装置是一同轴圆筒型的理想二极管及其测量系统,实验结果用计算机进行处理。由能谱分布曲线看出:电子的能量分布服从麦克斯韦分布;能谱半宽度随温度升高而增大,峰值对应的电压也随温度升高而增大。说明温度愈高,W的热电子能散度愈大,色差也越大。这些结果对正确使用W阴极,以及进一步提高各种电子光学仪器的分辨率有参考意义和实用价值。     

用AC15/1直流复射式检流计直接测量10~(-6)以下电流电压稳定度

在物理实验中经常使用的许多电子仪器,以及一些大型精密仪器,如电子显微镜、质谱仪、加速器等,对直流电源的稳定性都要求很高。 如在电子显微镜中高压的不稳定和透镜电流的不稳定都会引起象的模糊。当这种不稳定性超过一定限度,就影响象的分辨率。对于一定的分辨本领,可以计算出对电源稳定度的要求。 表(一)列出透射电子显微镜加速电压80千伏时,对一定分辨本领的高压稳定度值和透镜电流稳定度值。     

非中性相对论等离子体在脉冲星磁层中的运动

探讨了脉冲星磁层加速区外磁流管中非中性相对论等离子体的运动学特征.在满足净电荷密度处处等于Goldreich-Julian电荷密度的条件下,计算了不同磁倾角和不同磁力线上的次级正负电子速度分布.结果表明,电子速度经历显著的加速或减速.在靠近自转轴一侧的上半磁层和靠近赤道一侧的下半磁层,次级电子加速或减速的图像有显著不同.沿磁力线平行电场的总电压差所引起的电子动能改变与电子初始动能相当,但该电压差远小于磁层加速区的总电压差.该结果对研究磁层中粒子能谱的不均匀性是有意义的.     

棱镜、光栅的色散本领和色分辨本领

从棱镜和光栅的分光作用出发,讨论了棱镜和光栅的色散和色分辨本领,对棱镜和光栅的分光性能进行了分析和对比     

ω≈ωce区域内电子回旋波色散关系的非相对论研究

给出了非相对论情况下,电子回旋波热等离子体色散关系在ω≈ωce时的表达形式,并在非相对论的适用条件下取代热等离子体色散关系与冷等离子体色散关系进行了对比,计算了寻常波(O波)和非寻常波(X波)的波迹,结果表明,两种模型得出的结果差别很小。     

有色散项的一维分子晶体模型的孤子激发

本文得到了考虑了色散项后的一维分子晶体模型的孤子激发的运动解,在忽略了色散项的近似下,此运动解回复于通常极化子解。计算了模型中运动的自隐态的晶格位移,电子的自陷阱和电流密度以及孤子激发的峰值,峰宽,有效质量和束缚能以及Ｂｌｏｃｈ能带底部电子的的能量。     

Compton散射下激光等离子体与自生磁场对电子的加速

应用电子与多光子集团非线性Compton散射模型,对多光子非线性Compton散射下激光等离子体和自生磁场对电子的加速进行了理论分析和数值模拟.结果表明,不仅由Compton散射光与入射光形成的耦合光以及耦合光与等离子体相互作用形成的自生磁场所构成的混合场能使做回旋共振运动的电子在较短的长度内加速到很高的能量,而且注入电子的初始参数及耦合光的参数对电子加速亦有较大影响.     

计算机模拟反射式速调管中电子的运动

本文针对微波实验教学中,反射式速调管工作原理难以理解,影响实验正常进行的困难,对反射式速调管中电子的运动进行了计算机图形模拟.通过在模拟程序中对速调管反射极电压的改变,不仅可以观察电子运动的不同轨迹,而且还能模拟研究反射极电压与微波输出功率的关系,解决了微波实验教学中的难点,有效提高了实验课的教学质量.     

含非热电子的自引力尘埃系统中尘埃离声波的色散

基于等离子体动理论,研究了非热电子修正的尘埃离声波(DIAW)的色散关系,分析了自引力尘埃系统中非热电子对尘埃离声波色散的影响。结果表明,非热电子和尘埃自引力对尘埃离声波色散关系具有修正效应,分析易知,离声波的相速度随着非热指数的增大而减小,而群速度随非热指数增大而增大。此外,当电子非热指数ke→∞时,该修正的尘埃离声波的色散关系回到麦氏分布的情况。研究结果可以为天体物理和实验尘埃等离子体中观测到的现象提供理论参考。     

扫描电子显微镜的扫描电路研制

报导了采用高速、高精度、低噪声的数模转换器设计扫描电子显微镜的扫描电路,其扫描速率可达到每秒106像素,讨论了电路中的噪声对图像分辨率的影响,提出了一种矫正扫描线圈电感所引起的电流非线性的方法,应用到扫描电子显微镜DXP-10中,得到了较好的扫描图像.     

一种高性能电子枪的设计

通过增大聚焦极口径以提高电子束的利用率,保证阴极发射的电子全部打到荧光屏上,以实现提高亮度的目的.同时在聚焦极与阳极之间增加一个自由电位电极,该电极电位受聚焦极与阳极静电电压感应,形成界于聚焦极与阳极间的电压,该电压在电子枪内形成了另一个聚焦极,从而使从阴极发射出的电子在经过聚焦极聚焦后又进行了一次会聚,因而进一步提高了电子枪的分辨率.     

加速度效应对弹性海床动力反应的影响

基于u～U形式的广义Biot理论,探讨了土骨架和孔隙流体的加速度对波浪作用下弹性海床动力反应的影响。通过算例比较考察了Zienkiewicz等所提判断准则对均质海床的适用性。加速度效应影响程度主要取决于波浪周期、海床厚度和土体剪切模量,Zienkiewicz等所提判断准则并不总适用于判断加速度效应对海床动力反应的影响。一般来说,考虑海床土骨架和孔隙流体加速度与否得到的超静孔压幅值相差很小,但某些情况下不考虑加速度效应可能低估海床内的有效应力幅值,特别是剪应力幅值。     

Sub-ångstrom resolution using aberration corrected electron optics

Following the invention of electron optics during the 1930s, lens aberrations have limited the achievable spatial resolution to about 50 times the wavelength of the imaging electrons. This situation is similar to that faced by Leeuwenhoek in the seventeenth century, whose work to improve the quality of glass lenses led directly to his discovery of the ubiquitous "animalcules" in canal water, the first hints of the cellular basis of life. The electron optical aberration problem was well understood from the start, but more than 60 years elapsed before a practical correction scheme for electron microscopy was demonstrated, and even then the remaining chromatic aberrations still limited the resolution. We report here the implementation of a computer-controlled aberration correction system in a scanning transmission electron microscope, which is less sensitive to chromatic aberration. Using this approach, we achieve an electron probe smaller than 1 A. This performance, about 20 times the electron wavelength at 120 keV energy, allows dynamic imaging of single atoms, clusters of a few atoms, and single atomic layer 'rafts' of atoms coexisting with Au islands on a carbon substrate. This technique should also allow atomic column imaging of semiconductors, for detection of single dopant atoms, using an electron beam with energy below the damage threshold for silicon.     

Influence of pulse polarity on electron emission property of antiferroelectric ceramic

The electron emission property of a novel antiferroelectric cathode material lanthanum-doped lead zirconate stannate titanate （PLZST） on the application of positive or negative triggering voltage pulses has been investigated. All experiments were performed in a vacuum of 10-5 Torr and at room temperature. It was discovered that there were two electron emission pulses when low positive triggering voltage was applied to the rear electrode, and three electron emission pulses when high positive triggering voltage was applied. However there were always two electron emission pulses when negative triggering pulses were applied. This phenomenon is proposed to be a result of both field electron emission at triple junctions and electron emission caused by polarization reversal. The experimental observations indicate that domain movement in the vicinity close to the triple junction under applica- tion of the triggering voltage pulse may be a primary origin of electron emission from PLZST.     

对一种新型全有机复合薄膜的超高密度信息存储研究

用真空热壁法生长了一种新型全有机复合薄膜TTF/m-NBP(tetrathiofulvalene/m-nitrobenzylidene propanedinitrile)。用透射电子显微镜和傅立叶变换红外光谱对薄膜的表征结果证明,该制备方法能够生长出较大面积的化学结构完善的单晶薄膜。用原子力显微镜(AFM)和扫描隧道显微镜(STM)都观察到了TTF/m-NBP薄膜表面的原子级分辨像。通过STM针尖施加脉冲电压在TTF/m-NBP薄膜上实现了纳米级的信息存储,最小记录点直径约为1.2nm。扫描隧道谱分析表明TTF/m-NBP薄膜具有很好的电开关“记忆”特性。初步研究认为其电开关机制可能主要是脉冲电压诱发的TTF电子给体与m-NBP电子受体分子间的电荷转移的变化所致。     

Influence of low energy ballistic electron on the transmittance properties of Au/Si interface studied by ballistic-electron-emission microscope

Conclusions The electronic properties of Au/Si interface are investigated with a homemade ballistic-electron-emission microscope. The spatial distribution of Schottky barrier height is detected. Irreversible changes of ballistic transmittance of local interface with typical size of a few hundred of angstroms in diameter are observed by raising the tip voltage temporarily. Ballistic-electron-emission spectroscopy indicates that the electron transmission probabilities are reduced significantly inside the modified region, which is attributed to the Au-Si intermixing and other chemical reactions occurring at the interfacial layer stimulated by the injected energetic hot electrons.     

Fabry - Perot interference in a nanotube electron waveguide

The behaviour of traditional electronic devices can be understood in terms of the classical diffusive motion of electrons. As the size of a device becomes comparable to the electron coherence length, however, quantum interference between electron waves becomes increasingly important, leading to dramatic changes in device properties. This classical-to-quantum transition in device behaviour suggests the possibility for nanometer-sized electronic elements that make use of quantum coherence. Molecular electronic devices are promising candidates for realizing such device elements because the electronic motion in molecules is inherently quantum mechanical and it can be modified by well defined chemistry. Here we describe an example of a coherent molecular electronic device whose behaviour is explicitly dependent on quantum interference between propagating electron waves-a Fabry-Perot electron resonator based on individual single-walled carbon nanotubes with near-perfect ohmic contacts to electrodes. In these devices, the nanotubes act as coherent electron waveguides, with the resonant cavity formed between the two nanotube-electrode interfaces. We use a theoretical model based on the multichannel Landauer-Büttiker formalism to analyse the device characteristics and find that coupling between the two propagating modes of the nanotubes caused by electron scattering at the nanotube-electrode interfaces is important.     

低硬度P91钢弯头的组织与性能分析

火力发电通过提高发电机组的蒸汽参数可以获得更高的发电效率,但更高的蒸汽参数给火电厂的安全运营带来新挑战。蒸汽管道弯头是火电机组系统中的事故多发区,其组织性能的研究对于指导管件生产与电厂设备运营管理具有重要意义。某电厂某1 000 MW超超临界机组在进行金属监督检验时,发现材质为P91钢的管道弯头背弧面局部硬度偏低。通过硬度试验、拉伸试验、金相检测、扫描电子显微镜、透射电子显微镜等分析,对其硬度偏低部位的显微组织与力学性能进行研究。经分析,P91弯头局部区域硬度偏低的主要原因是组织老化、析出相长大导致其各项强化作用减弱。     

Mn-Si 系多层焊焊缝侧弯形貌的研究

本文通过焊接接头侧弯试验、光学显微镜和扫描电镜分析，对Ｍｎ－Ｓｉ系多层焊焊缝侧弯形貌进行了研究，探讨了侧弯形貌与焊接热循环、焊接线能量及显微组织之间的关系。研究表明，焊缝侧弯形貌分析是了解Ｍｎ－Ｓｉ系多层焊焊缝变形能力的一种直观有效的途径。