Direct observation of the initial process of Ostwald ripening using spherical aberration-corrected transmission electron microscopy

We study in situ behavior of platinum single atoms on amorphous carbon (a-carbon) using a spherical aberration-corrected transmission electron microscope (AC-TEM). Diffusion of single atoms, bi-atoms, clusters (<1?nm) and nanoparticles (<3?nm) was recorded in the same image with a time resolution of 1?s, and such diffusion matches the expected mechanism of Ostwald ripening, which was seen on these samples. In situ AC-TEM shows promise for dynamical observation of single atom diffusion, which is important for understanding nanosized catalysts and ceramic sintering processes. We apply in situ AC-TEM to image platinum (Pt) nanoparticles on a-carbon, which is a model catalyst system for the real Pt electrode catalysts using alloys and core-shell structures supported on carbon/oxide composite materials in the proton exchange membrane fuel cell.     

Fabrication of periodical nanostructures using electron interference fringes

A scanning interference electron microscope (SIEM) has been developed for periodical nanostructure fabrication. This system can produce electron interference fringes with a period from 2 nm to several ten microns. Fabrications of periodical nanostructures with 23 to 170 nm period have been demonstrated by transferring electron interference fringe onto semiconductor surfaces.     

电子全息的数字重现及其在微电磁场测量中的应用

阐述了用数」字方法重现电子全息图及实现噪声消除、位相差放大的基本原理,将它应用到微电磁场测量中,给出了实验结果,报道了光学重现未能观测到的新现象。     

静脉留置针针头表面附着物的扫描电镜观察

探讨静脉穿刺留置针易引发静脉炎的因素,收集临床患者留置针针头,常规方法制作扫描电镜样品,扫描电镜下观察针头表面附着物情况,发现冠心病患者的针头附着物高于心脏器质性病变患者针头附着物,提示患者疾病与静脉炎有一定的关系。     

Three-dimensional reconstructions of electrostatic potential distributions with 1.5-nm resolution using off-axis electron holography

Three-dimensional (3D) reconstruction experiments were carried out by observing high-resolution 3D electrostatic potential distributions of Pt nanoparticles using off-axis electron holographic tomography. These Pt nanoparticles were mounted on the surfaces of amorphous silicon pillars. In order to realize high-resolution observation, we developed a mechanically stable 3D specimen holder with small specimen drifts and vibrations. From the 3D electrostatic potential distribution data of Pt nanoparticles (2.0?nm in diameter), we obtained the resolution of 1.5?nm.     

Theory of periodic electrostatic focusing of electron beams

A general theory of periodic electrostatic focusing structures in micowave tubes is presented. A general method for evaluating the properties of focusing systems is developed. The method is based on the use of the Action Function and is applicable to structures whose potential distribution can be found by the method of separable variables. It is shown that this approach can yield results similar to, but more exact, than those obtained by the classical paraxial ray equation. The basic and double-ring structures have been examined in detail. Parameters describing these structures are presented in graphical and tabular form. It is shown that for irrotational flow, a specific current distribution is required. The use of computer techniques for the solution of electron flow problems is discussed. A computer analysis has been developed and results obtained are discussed. The accuracy of the Action Function and the computer analyses has been verified experimentally. It has been shown that the focusing potentials predicted by the Action Function analysis are in good agreement with the experimental values. The computer analysis has also been shown to give results comparable with those obtained practically. Hollow beams of 3.85, 5.4, and 15.6 µP have been focused using the basic ring structure. In order to investigate the effect of unbalance of focusing and defocusing forces at the inner beam boundary, pinhole measurements have been made. It is shown that the ring structure focuses a hollow beam with some change in the beam cross section. The effect of the unbalance of forces is to transform the current density profile. Results indicate that the transformation is desirable since a beam of constant current density may be transformed to a distribution which approaches that required for irrotational flow.     

Multiresolution analysis of electrostatic discharge current from electromagnetic interference aspects

This paper reports an analysis of the electromagnetic interference (EMI) aspects of electrostatic discharge (ESD) resulting from high-speed moving discharge phenomena. An orthogonal wavelet transform, which enables multiresolution decomposition of time-domain waves, was used to analyze measured ESD currents. The results showed that the high-speed moving discharges can increase the maximum amplitude and power of ESD currents, and that high-frequency components in particular tend to be affected by the movements of discharge electrodes. In the case of high-frequency components of ESD currents generated by charging voltages of 2, 5, and 15 kV, it was observed that the maximum amplitude was increased by 1.40 to 3.43 times, and the energy, defined by the sum of signals squared, was increased by 2.15 to 12.1 times compared to the results for the low-speed discharges. Chaos attractors reconstructed from measured ESD currents also showed that high-speed moving discharges decrease the stability of ESD current waveforms. From these results, it is apparent that EMI power generated by ESD tends to increase in the case of high-speed moving discharges.     

二维双观测站纯方位系统的可观测性

在二维空间中,针对作匀加速直线运动的目标,利用双观测站得到的测量角,讨论了等速直线运动的双观测站纯方位系统的可观测性问题.首先在理论上证明了目标作匀加速直线运动,单观测站作匀速直线运动时的目标参数的部分可观测性.进而对于双观测站情形,利用每一个观测站求解出的关于目标的部分参数满足的方程,通过研究方程组的解的存在性,得到了整个系统可观测的一些充分条件和一个充要条件.     

Examination of electrostatic potential distribution across an implanted p-n junction by electron holography

In the manufacture of semiconductor microelectronic devices, a p-n junction is formed usually by implanting a high concentration of impurity into a less heavily doped region and then heat annealing. A Si/Si p-n junction test sample has been made following the above practical process and thinned for electron holographic observation by using argon ion-milling. From the reconstructed phase image, the phase shift induced by potential drop across p-n junction can be seen clearly. To characterize quantitatively this potential drop, the mean inner potential V0 of silicon was measured precisely by electron holographic method. By measuring 25 different crystalline silicon spheres with diameter ranging from 40 to 170 nm, an average result of V0 = 12.16 +/- 0.83 V was obtained. By using this V0 value, a quantitative measurement yields the potential drop approximately 0.70 V, which is reasonably consistent with expected Si/Si junction parameter. The thickness of electric dead layer in depletion region produced from this measuring is approximately 20 nm on each sample surface.     

Electromagnetic interference mitigation by using a spread-spectrumapproach

We investigate a new technique, referred to as spread-spectrum clock generation (SSCG), for reducing the level of radiated emission from devices with digital clock signals. To calculate the radiated emissions from such devices, we model the radiating geometry and compute the radiated field at a multitude of frequencies by using NEC-4, which is an electromagnetic field solver based on the method of moments (MoM). We consider a variety of modulating profiles for the spread spectrum clock and demonstrate that by using a frequency deviation of only 1%, we can achieve from 10 to 30 dB reduction in the radiated emission levels     

Hybrid computer aided design of thick electrostatic electron lenses

The synthesis of space charge free electron lenses can be approached by first assuming solutions for Laplace's partial differential equation in terms of cylindrical harmonics. The hybrid computer can quickly generate these assumed solutions and their gradient by working with the differential equations obtained from product separation of variables. The gradient is used in the integration for the trajectory to determine if the lens is useful. If so, either equipotential surfaces or the potentials along a desired surface are generated with the computer to guide the physical realization of the lens. Certain cases where space charge cannot be neglected are solved by truncation of rectilinear electron flow. Poisson's equation is solved in the computer to serve as a Cauchy boundary condition to Laplace's equation outside the electron beam. The hybrid computing technique and the experimental verification of some of the results in cathode-ray tube electron lenses are presented.     

朗谬尔探针法测量横流CO_2激光器的电子密度

本文讨论了探针在流动等离子体中的鞘层变化,在厚鞘层情况下,用朗谬尔探针测量了在不同偏压和主放电电流下的离子电流,并计算出不同放电电流下的电子密度,给出了电子密度的顺流分布。     

Direct observation of Cu,Zn cation disorder in Cu2ZnSnS4 solar cell absorber material using aberration corrected scanning transmission electron microscopy

Chemical analysis of individual atom columns was carried out to determine the crystal structure and local point defect chemistry of Cu₂ZnSnS₄. Direct evidence for a nanoscale composition inhomogeneity, in the form of Zn enrichment and Cu depletion, was obtained. The lateral size of the composition inhomogeneity was estimated to be between ~1.5 and 5 nm. Photoluminescence confirmed the presence of a broad donor–acceptor transition consistent with the observed cation disorder. Areas of relatively high concentration of Zn_Cu⁺ antisite atom donors locally increases the electrostatic potential and gives rise to band bending. Troughs in the conduction band and peaks in the valence band are ‘potential wells’ for electrons and holes, respectively. For a solar cell, these prevent minority carrier electrons from diffusing towards the edge of the space charge region, thereby reducing the carrier separation efficiency as well as reducing the carrier collection efficiency of majority carrier holes. Furthermore, electrons and holes ‘trapped’ within potential wells in close proximity have a high probability of recombining, so that the carrier lifetime is also reduced. High quality Cu₂ZnSnS₄ crystals free from composition inhomogeneities are therefore required for achieving high efficiency solar cell devices. Copyright © 2012 John Wiley & Sons, Ltd.     

棱镜全息干涉法制作二维光子晶体的研究

模拟了Top-cut棱镜全息干涉生成的各种光学晶格结构,为棱镜法制作光子晶体提供参考。用全息干涉理论分析了top-cut六棱镜多光束干涉生成的光学晶格结构,考虑了光束数目、偏振方向以及位相的不同对晶格结构的影响。改变光束数目可以生成不同周期的正六角、斜六角光学晶格;改变光束偏振特性则影响光学晶格格点的形状;改变光束初位相可以生成蜂窝状结构等。另外还模拟了top-cut五棱镜所生成的十重旋转对称光学准晶结构。并且用平面波展开法计算了六角和蜂窝结构的有机光子晶体带隙图,证明了蜂窝结构更容易产生大的光子带隙。     

静电摇摆器自由电子激光的自发辐射

基于静电摇摆器中电势场的一种典型二维模型 ,在小振幅振动情况下讨论了相对论电子束在其中的运动规律 ,计算得到了该类型自由电子激光的自发辐射谱。上述结果与平面磁摇摆器有类似的形式     

Space charge effects and stability of electron motion in the electrostatic electron cyclotron resonance maser

The paper deals with the space charge effects and the stability of electron motion in the electrostatic electron cyclotron resonance maser (EECRM). The complete dispersion equation of EECRM is obtained and two types of instability included in it are analysed. The results indicate that: (a) there exists a critical value for the electrostatic potential which affects the inherent oscillation in the EECRM system; (b) the frequency of the inherent oscillation increases when the DC space charge effect is taken into consideration; (c) the inherent oscillation instability may still exist in non-relativistic mode; and (d) the space charge effect is conducive to the synchronous instability and it increases the growth rate of instability.