Two-dimensional electron gas base hot electron transistor

Presents data on a large area hot-electron transistor in the GaAs/AlGaAs materials system that uses a two-dimensional electron gas for its base. When the feature size is scaled from the present 100 mu m (approximately) to 1 mu m, the authors predict useful transistor action at 100 GHz.<>     

Secondary electron detection for distributed axis electron beam systems

A secondary electron detection scheme for the distributed axis, fixed-aperture system is described. It employs a multi-channel detector array with a through-hole for a primary beamlet on each channel, a field terminator installed between the detector array and sample, and a deflector forming a static transverse electric field between the field terminator and sample. These elements enable detection of the secondary electrons stimulated by the primary beamlet. In order to achieve a high detection rate, small separation of the primary beamlets, and small aberrations, the size and the layout of the through-holes of the field terminator are studied. The equation of motion in an ideal field distribution is analytically solved and the dispersion of the secondary electrons caused by the helical motion in an axial magnetic field and chromatic variation of deflection are calculated. Aberrations are calculated by using numerical simulation. On the basis of these calculations, two types of the field terminator are proposed. One has a single through-hole, which is shared by a primary beamlet and the secondary electrons stimulated by the primary beamlet, per primary beamlet. The other has a through-hole exclusively for a primary beamlet and an extra slot for the secondary electrons, per primary beamlet. Simulations reveal that the former achieves a secondary electron detection rate of 99.7% and aberrations smaller than 4.6 nm, but doesn’t enable the separation of the primary beamlet to be smaller than 1000 μm. In contrast, the latter achieves a secondary electron detection rate of 95.0%, aberrations smaller than 9.7 nm. Furthermore, it also enables the separation of the primary beamlet to be as small as 250 μm, the same as in our detector array at this moment.     

透射电镜与扫描电镜分析

文章简要介绍了透射电镜和扫描电镜两种当前主要的电子显微分析方法的应用,比较了它们的结构和工作原理,讨论了各自的应用范围以及发展方向,指出将两者有机结合可以得到比较全面的材料分析结果。     

Chaotic electron trajectories in a circular free electron laser

The motion of a relativistic electron is analyzed in the field configuration consisting of a circular wiggler magnetic field, an axial magnetic field, and the equilibrium self-electric and self-magnetic fields produced by the non-neutral electron ring. By generating Poincare surface-of-section maps, it is shown that when the equilibrium self-fields is strong enough, the electron motions become chaotic. Although the realistic circular wiggler magnetic field destroys the integrability of the electron motion as the equilibrium self-fields do, the role the latter plays to make the motions become chaotic is stronger than the former. In addition, the axial magnetic field can restrain the occurrence of the chaoticity.     

CHAOTIC ELECTRON TRAJECTORIES IN A CIRCULAR FREE ELECTRON LASER

The motion of a relativistic electron is analyzed in the field configuration consisting of a circular wiggler magnetic field, an axial magnetic field, and the equilibrium self-electric and self-magnetic fields produced by the non-neutral electron ring. By generating Poincare surface-of-section maps, it is shown that when the equilibrium self-fields is strong enough, the electron motions become chaotic. Although the realistic circular wiggler magnetic field destroys the inte-grability of the electron motion as the equilibrium self-fields do, the role the latter plays to make the motions become chaotic is stronger than the former does. In addition, the axial magnetic field can restrain the occurrence of the chaoticity.     

定量三维电子显微术及三维电子衍射

用电子晶体学可以确定尺度在微米甚至纳米级晶体的原子结构。它所要求的晶体尺寸比X射线晶体学所需的小百万倍。确定晶体的原子结构既可通过对高分辨电子显微像作图像处理,也可直接用电子衍射数据。同时还可将高分辨电子显微像和电子衍射数据与X射线粉末衍射结合起来确定晶体结构。如果晶体的单胞很大,原子在任何方向上的投影都有重叠,确定晶体的原子结构则需要拍摄一系列不同晶带轴的电子衍射图及高分辨像,再将其综合起来重构晶体的三维静电势图,以得到晶体的原子位置。本文将概括地介绍最近十几年中电子晶体学的一些最新进展及其在无机晶体结构解析方面的一些最新应用实例。     

Convergent-beam electron diffraction

This paper reviews the convergent-beam electron diffraction (CBED) technique. Point- and space-group determination methods of ordinary crystals are described, along with an example of the determination method for Sr?Ru?O?. The symmetry determination of one-dimensionally incommensurate crystals and quasicrystals is explained. The large-angle CBED technique, which is indispensable for lattice defect and lattice strain analysis, is also described. A real procedure for lattice strain analysis is provided, using an example of a multilayer Si?-xGe(x)/Si material. A nanometer-scale crystal structure refinement method and charge density and crystal potential determination method by CBED are briefly described.     

From electron energy-loss spectroscopy to multi-dimensional and multi-signal electron microscopy

This review intends to illustrate how electron energy-loss spectroscopy (EELS) techniques in the electron microscope column have evolved over the past 60 years. Beginning as a physicist tool to measure basic excitations in solid thin foils, EELS techniques have gradually become essential for analytical purposes, nowadays pushed to the identification of individual atoms and their bonding states. The intimate combination of highly performing techniques with quite efficient computational tools for data processing and ab initio modeling has opened the way to a broad range of novel imaging modes with potential impact on many different fields. The combination of Angstr?m-level spatial resolution with an energy resolution down to a few tenths of an electron volt in the core-loss spectral domain has paved the way to atomic-resolved elemental and bonding maps across interfaces and nanostructures. In the low-energy range, improved energy resolution has been quite efficient in recording surface plasmon maps and from them electromagnetic maps across the visible electron microscopy (EM) domain, thus bringing a new view to nanophotonics studies. Recently, spectrum imaging of the emitted photons under the primary electron beam and the spectacular introduction of time-resolved techniques down to the femtosecond time domain, have become innovative keys for the development and use of a brand new multi-dimensional and multi-signal electron microscopy.     

Hot electron spectroscopy

Using a modified GaAs planar doped barrier transistor, grown by MBE, we are able to determine the nonequilibrium distribution function of hot electrons arriving at the base/collector junction. Knowledge of the electron distribution allows one to determine the physical processes necessary for the understanding of hot electron transport which assumes prominence as device dimensions decrease.     

Scanning electron mirror microscopy and scanning electron microscopy of integrated circuits

The recently developed scanning electron mirror microscope (SEMM) is compared with other types of electron microscopes, such as the electron mirror microscope (EMM) and the scanning electron microscope (SEM), for examining integrated circuits. Potential advantages of the SEMM include high resolution, elimination of electron bombardment damage, and high sensitivity of voltage gradients, magnetic fields, and topography. Preliminary observations of integrated, circuits obtained with the feasibility SEMM at various specimen potentials are discussed.     

Free electron laser spectral dynamics with a modulation of electron beam energy

Recent experimental and theoretical works on free electron laser spectral dynamics have pointed out the difficulty to obtain a narrow and stable spectrum operation. This goal can only be achieved by avoiding the sideband generation leading to a broadband and unstable spectrum. Tapered wiggler and two-frequency wiggler are well suited for combining sharp spectrum and high efficiency but are not really compatible with a wide tunability of laser light. Filtering sidebands is a good way for lower power experiments but it seems to be difficult to conceive wideband filters, specially in the far-infrared region. Modulation of electron energy is a new potential soft way for controlling the spectral dynamics of longpulse free electron laser. Spectral dynamics under the modulation is investigated in the linear and non-linear regimes in the far-infrared region. Simulations show that a pulsed and sharp spectrum behavior can be obtained by optimizing the modulation parameters. The interest of such a method for the far-infrared experiments is discussed.     

In-the-lens secondary electron analyser for IC internal voltage measurements with electron beams

A new analyser scheme for voltage measurements on integrated circuits is described. The analyser is built into the objective lens of a scanning electron microscope. It features small working distances, high voltage resolution capability, high transmission, and reduced sensitivity to measurement errors.     

Embedment-free section electron microscopy

Because of potential hindrance of clear viewing in epoxy sections of biological entities having an electron density similar to and lower than that of epoxy resin, the author has stressed that the embedment-free section electron microscopy is necessary for re-examination and/or clarification of biological specimen structures, and that the embedment-free electron microscopy is reliably done by using water-soluble polyethylene glycol (PEG) as a transient embedding media and by critical point-drying of embedment-free sections after de-embedment of PEG by immersion of semithin sections into water. With the embedment-free electron microscopy, the author has presented five major findings: the appearance of microtrabecular lattices with different compactnesses in various cells and in intracellular domains of a given cell, the faithful reproduction of microtrabecula-like strand lattices in vitro with increasing compactnesses from artificial protein solutions at correspondingly increasing concentrations, the appearance of more compact lattices from gelated gelatin than from solated gelatin at a given concentration in vitro, the changeability in compactnesses of the microtrabecular lattices by hyper- or hypotonic shock treatments of cells, and the confined appearance of an intracellular protein in the centripetal demilune of centrifuged ganglion cells which is occupied with the microtrabecular lattices of a substantial compactness. From these findings, several conclusions are drawn: individual strands themselves of the microtrabeculae are meaningless, the appearance of microtrabeculae represents the presence of proteins at a certain concentration, and it is therefore likely that the aqueous cytoplasm is equivalent to the aqueous solution. In addition, it is possible that the appearance of two contiguous lattice domains exhibiting different compactnesses in a given cell may represent the occurrence of a contiguity of sol to gel states of cytoplasmic domains. It is thus proposed that the localization and movement of intracellular organelles are controlled not only by the cytoskeletons but also by the concentration and sol/gel states of intracellular proteins. In addition, several potential usefulness of the embedment-free electron microscopy has also been demonstrated.     

An electron beam maskmaker

An electron beam machine is described, in which the ¼-µm diameter beam is computer controlled to define integrated circuit and other fine patterns at their final size in response to a coordinate data input. Electron sensitive resist is exposed on metallized quartz or glass substrates. Resist development followed by metal etching enables masks to be made, either for subsequent photolithography or, more usually, for use in the electron image projector developed by J. P. Scott. The mask drawing process is entirely automatic and the emphasis is on the rapid generation of complex patterns with high precision. A two-stage deflection system enables rectangular pattern elements to be drawn at a 10-MHz stepping rate and accurately positioned throughout a 2-mm square main deflection field. Patterns are automatically positioned, to an accuracy of ±1/8 µm, relative to an array of markers predeposited on the substrate. The beam is also refocused automatically at the markers. A mechanical stage for the substrate enables 50 × 50-mm arrays of patterns to be built up. A complete mask containing detail as small as 1 µm takes 1-3 h to draw. Finer patterns can be drawn, although more slowly.     

自由电子激光器评述

自由电子激光器是地基激光武器的首选器件。本文评述自由电子激光器的研究现状和发展动态.特别是射频自由电子激光器和感应型自由电子激光器,近年来,它们已成了世界上许多国家的主要研究对象。     

Resonant tunnelling electron spectroscopy

The energy distribution of hot electrons quasiballistically injected in p+ GaAs has been probed directly using the tunnelling resonances of a double barrier in a specially designed two-terminal heterojunction device. The photocurrent/voltage characteristics give direct information on the hot electron spectrum, without requiring derivative techniques.     

A pseudo-lucky electron model for simulation of electron gatecurrent in submicron NMOSFET's

An energy parameterized pseudo-lucky electron model for simulation of gate current in submicron MOSFET's is presented in this paper. The model uses hydrodynamic equations to describe more correctly the carrier energy dependence of the gate injection phenomenon. The proposed model is based on the exponential form of the conventional lucky electron gate current model. Unlike the conventional lucky electron model, which is based on the local electric fields in the device, the proposed model accounts for nonlocal effects resulting from the large variations in the electric field in submicron MOSFET's. This is achieved by formulating the lucky electron model in terms of an effective-electric field that is obtained by using the computed average carrier energy in the device and the energy versus field relation obtained from uniform-field Monte Carlo simulations. Good agreement with gate currents over a wide range of bias conditions for three sets of devices is demonstrated     

Double-stream electron cyclotron maser

A new mechanism for stimulated radiation combining the cyclotron instability with the plasma double-stream instability is presented. It can be regarded as a new type of electron cyclotron resonance maser (ECRM) (Hirshfield 1979, Liu 1979) as well as a two-stream free-electron laser (FEL) (Piestrup 1981, Bekefi and Jacobs 1982) in a broader sense. One can say that this device combines ECRM and the two-stream FEL into one. The linear theory of the double-stream ECRM is given. Numerical calculations show that it offers the attractive advantages of high gain and broadband as compared with the conventional ECRM.     

Fast electron beam scanlaser

The electron beam scanlaser (EBS) is a device in which a modified electrooptic light valve is used as a mode selector in the highly degenerate flat-field conjugate laser resonator to provide a scanning light spot. This paper describes improvements in the mode selection portion of the EBS which make the device far more promising. In particular, 1) the charge storage time is now under control, and can be as short as needed, 2) the KDP is protected from the electron beam, 3) the electron gun is protected from the KDP, 4) provision can be made for the needed high-quality optical surfaces in the mode selector, and 5) the transparent conducting coating on the mode selector's KDP crystal has been removed, indicating that the insertion loss of the mode selector can be reduced to less than 1.5 percent.