A fast beam switch for controlling the intensity in electron energy loss spectrometry

The fast deflection system described in this paper is suitable for controlling the intensity reaching the detector of a magnetic sector electron spectrometer mounted below an analytical transmission electron microscope. Amongst other things, this allows the low loss region of the spectrum to be recorded with the same electron probe conditions used to record core losses, something that is essential for high spatial resolution studies. The plate assembly restricts the width of the electron distribution reaching the viewing screen to a strip approximately 17 mm wide in the direction approximately normal to the dispersion direction of the spectrometer. The resulting deflection has no detectable effect on the FWHM of the zero-loss peak for exposure times as short as 1 micros. At incident energies up to 300 keV, positioning the deflection plates in the 35 mm camera port above the viewing chamber allows voltages of < +/- 3 kV to deflect the electrons out of the spectrometer and beyond the edge of the annular detector. When the deflection is switched on, the electrons are deflected out of the spectrometer in < 40 ns and when the deflection is switched off, the electrons return to within 10 microm of the undeflected position within 100 ns. Thus, even at an exposure time of 30 micros, the smallest time likely to be used in practice with a GATAN 666 spectrometer, < 1% of the signal in the spectrum is from electrons whose scattering conditions differ from those in the undeflected position. The performance of the deflection system is such that it will also be suitable for use with the new and much faster GATAN ENFINA spectrometer system. At incident energies up to 200 keV and possibly up to 300 keV, deflection voltages of +/- 3 kV are sufficient to deflect the electrons off a 1 k x 1 k charge coupled device (CCD) camera placed below the photographic camera. Thus the deflection system can be used as a very fast, non-mechanical shutter for such a CCD camera.     

Modular software platform for low-dose electron microscopy and tomography

Transmission electron microscopy imaging protocols required by structural scientists vary widely and can be laborious without tailor-made applications. We present here the jeol automated microscopy expert system ( james ) api integrator , a programming library for computer control of transmission electron microscopy operations and equipment. james has been implemented on JEOL microscopes with Gatan CCDs but is designed to be modular so it can be adapted to run on different microscopes and detectors. We have used the james api integrator to develop two applications for low-dose digital imaging: james imaging application and the mr t tomographic imaging application. Both applications have been widely used within our NCRR-supported Center for routine data collection and are now made available for public download.     

A high-sensitivity CCD system for parallel electron energy-loss spectroscopy (CCD for EELS)

A cooled frame transfer CCD camera system was developed and tested as a parallel detector in an electron energy-loss spectrometer mounted on a transmission electron microscope. The use of a shutterless camera with a frame transfer CCD collected virtually 100% of the photon signal with a reasonably fast acquisition time. The system detective quantum efficiency was over 90% under normal experimental conditions. Because of the low channel to channel gain variations in the CCD, the signal-to-noise ratio and the detection limit were substantially better than that obtained with a silicon intensified target (SIT) camera, and direct fitting to the standard data was feasible. Quantitation at the phosphorus L edge generated from a phosphoprotein, Phosvitin, showed that, under identical experimental conditions, direct fitting of spectra obtained with this CCD system gave better sensitivity than that given by the SIT camera system. Because of its larger pixel charge well, the CCD system can also operate at a much higher beam current, resulting in a significant reduction in the time required for elemental mapping at a given sensitivity.     

星载多光谱CCD相机研究

研制的星载多光谱 CCD相机采用线阵 CCD推扫方式成像 ,具有蓝、绿、红、近红外、全色五个成像谱段 ,在轨工作时地面像元分辨率为 2 0米 ,覆盖宽度 113公里。相机光学系统采用单镜头焦面分色结构实现多光谱成像 ,每个谱段的探测器阵列由 3片 2 0 4 8元 CCD光学拼接而成 ,以实现地面宽覆盖成像。多片 CCD信号采用串行读出方式 ,使焦面 15片 CCD形成两路视频信号输出给数据传输系统。测试结果显示 ,相机各谱段 MTF典型值为 0 .2 5 ,满足使用要求。     

Towards sub-0.5 A electron beams

In the 4 years since the previous meeting in the SALSA series, aberration correction has progressed from a promising concept to a powerful research tool. We summarize the factors that have enabled 100-120kV scanning transmission electron microscopes to achieve sub-A resolution, and to increase the current available in an atom-sized probe by a factor of 10 and more.Once C(s) is corrected, fifth-order spherical aberration (C(5)) and chromatic aberration (C(c)) pose new limits on resolution. We describe a quadrupole/octupole corrector of a new design, which will correct all fifth-order aberrations while introducing less than 0.2mm of additional C(c). Coupled to an optimized STEM column, the new corrector promises to lead to routine sub-A electron probes at 100kV, and to sub-0.5A probes at higher operating voltages.     

Construction of 35-millimeter camera adaptors for scanning electron microscopes

Described here is the construction of two 35-mm camera adaptors for attachment to the recording monitors of scanning electron microscopes (SEM). The designs are simple and readily adaptable to almost any SEM. The choice of this camera format for recording SEM images is one of convenience as well as economy and does not sacrifice micrograph quality.     

Comparison of electron diffraction data from non-linear optically active organic DMABC crystals obtained at 100 and 300 kV

During the recent past, we have synthesized a new class of molecules with intramolecular two-dimensional charge transfer upon excitation. The present report presents such a molecule, 2,6-bis(4-dimethylamino-benzylidene)-cyclohexanone (DMABC), with an unusually high value of the second-order non-linear optical (NLO) coefficients. In order to optimize the macroscopic NLO properties of the compounds, it is necessary to relate their first hyperpolarizability tensors at a molecular level to those at a crystal bulk level. This requires a complete structure determination and refinement. However, the growth of sufficiently large single crystals, which are needed for structural analysis and refinement by X-ray methods, is a time consuming and sometimes impossible task. We have performed a complete structural analysis by electron diffraction combined with simulation methods and with maximum entropy and log likelihood statistics. In order to improve the quantitative analysis, a 300 kV data set using an on-line CCD camera was added and the best attainable R-values were compared with those from 100 kV data using film emulsions. Details regarding the maximum attainable resolution for both data sets are discussed as well as the problems which arise from the limited dynamic range in photographic emulsions as compared to a 14 bit CCD camera. Once the crystal structure was known, quantum-chemical methods were used to calculate non-linear optical susceptibility tensor components and these were related to the macroscopic coefficients of the crystalline quadratic non-linearity tensor. In the present work, both ab initio and semi-empirical quantum-chemical calculations were employed.     

A comparison of conventional Everhart-Thornley style and in-lens secondary electron detectors: a further variable in scanning electron microscopy

The secondary electron (SE) imaging of several samples across a range of scanning electron microscopes (SEM) and SE detectors under matched operating conditions has generated a highly variable image data set. Using microanalytical conditions (10-15?kV), images from in-column SE detectors reveal the presence of surface films and contaminants that are invisible to conventional Everhart-Thornley SE detectors under the same conditions. Data from studying the effects of working distance, the image resolution derived through contrast transfer function analysis and electrostatic mirror imaging of the SE detectors in operation combine with other studies to suggest that the classically defined SE1 component can be separated from other SE components. SE images obtained by tailored mechanical design and energy-filtering will provide SE images with probe-sized resolution and dominated by surface detail currently only seen in low-voltage SEM, potentially even from thermionic-sourced columns.     

线阵-面阵CCD三线阵立体测绘相机焦平面组件的研制

介绍了线阵-面阵CCD(LMCCD)制式相机的相关原理,提出实现LMCCD相机的关键在于相机焦平面组件的研制.给出了LMCCD相机焦平面组件在研制过程中的关键技术,如LMCCD像面基板与CCD的高精度拼接,焦平面组件电子学部分的低噪声、高集成度设计,焦平面组件在真空环境下的热噪声抑制和热传导设计,以及焦平面组件的装配和焊接等.最后,给出了研制和测试结果.LMCCD拼接的共面精度优于5 μm,平移量和平行度均优于2μm;在典型工作情况下,实验室测试信噪比优于90;在15 min的工作周期下,焦面组件的温度控制在30℃以下.这些结果满足LMCCD制式相机关于CCD拼接、焦面温度控制和信噪比的要求.     

Evaluation of a hybrid pixel detector for electron microscopy

We describe the application of a silicon hybrid pixel detector, containing 64 by 64 pixels, each 170 microm(2), in electron microscopy. The device offers improved resolution compared to CCDs along with faster and noiseless readout. Evaluation of the detector, carried out on a 120 kV electron microscope, demonstrates the potential of the device.     

A software package for the processing and reconstruction of electron holograms

Electron holography is leaving its state of infancy and is rapidly becoming a tool for everyday use. This is due to the increasing availability of field-emission electron microscopes as well as the increasing use of slow-scan CCD cameras, which provide the linear image recording so essential to electron holography. At the same time, the continuing boost in performance of desktop computers both in hardware and in software has facilitated the handling of many of the complex reconstruction and processing tasks of electron holography. We describe here the software package ‘HoloWorks©’, recently developed at Oak Ridge National Laboratories. This package is designed for the processing of electron holograms stressing easy-to-use functions and is a plug-in module for Gatan's software DigitalMicrograph®.     

Effects of focused ion beam milling on electron backscatter diffraction patterns in strontium titanate and stabilized zirconia

This study investigates the effect of focused ion beam (FIB) current and accelerating voltage on electron backscatter diffraction pattern quality of yttria-stabilized zirconia (YSZ) and Nb-doped strontium titanate (STN) to optimize data quality and acquisition time for 3D-EBSD experiments by FIB serial sectioning. Band contrast and band slope were used to describe the pattern quality. The FIB probe currents investigated ranged from 100 to 5000 pA and the accelerating voltage was either 30 or 5 kV. The results show that 30 kV FIB milling induced a significant reduction of the pattern quality of STN samples compared to a mechanically polished surface but yielded a high pattern quality on YSZ. The difference between STN and YSZ pattern quality is thought to be caused by difference in the degree of ion damage as their backscatter coefficients and ion penetration depths are virtually identical. Reducing the FIB probe current from 5000 to 100 pA improved the pattern quality by 20% for STN but only showed a marginal improvement for YSZ. On STN, a conductive coating can help to improve the pattern quality and 5 kV polishing can lead to a 100% improvement of the pattern quality relatively to 30 kV FIB milling. For 3D-EBSD experiments of a material such as STN, it is recommended to combine a high kV FIB milling and low kV polishing for each slice in order to optimize the data quality and acquisition time.     

Evaluation of high-resolution electron microscopy as a method for studying Y-Ba-Cu-O superconductors

High-resolution transmission electron microscopes operating at 300 and 400 kV were used to investigate the crystallography and microstructure of the perovskitelike YBa₂Cu₃O_7−x. In this paper, we evaluate the performance attainable with these microscopes both empirically and by computer modelling. Based upon the assumption that oxygen may be a key to superconductivity properties, we have also investigated the visibility of the oxygen sites as well as the heavier yttrium and barium ion positions and the lighter Cu atom positions. We propose a scheme for observing different twin orientations in these structures and hence the oxygen atom positions seen in projection for the [100] and [010]. Our observations of both thick and thin regions of Y-Ba-Cu-O materials are reported as well as the problems of adjusting microscope parameters and specimen alignment to obtain interpretable images. We also give a preliminary report on the effects of heat treatment as seen in high-resolution micrographs to assess disorder of the heavy atoms and oxygen vacancies.     

Improvements in the fabrication of thin foil apertures for electron microscopy

Schabtach (1974) developed a process for making ‘thin’ (i.e. self-cleaning) apertures for electron microscopes. Several improvements in this process are described, the most important of which is the deposition of a heavy metal by DC sputtering rather than by evaporation, making the process much easier.     

Characterization of a direct detection device imaging camera for transmission electron microscopy

The complete characterization of a novel direct detection device (DDD) camera for transmission electron microscopy is reported, for the first time at primary electron energies of 120 and 200 keV. Unlike a standard charge coupled device (CCD) camera, this device does not require a scintillator. The DDD transfers signal up to 65 lines/mm providing the basis for a high-performance platform for a new generation of wide field-of-view high-resolution cameras. An image of a thin section of virus particles is presented to illustrate the substantially improved performance of this sensor over current indirectly coupled CCD cameras.     

Energy filtering transmission electron microscopy using the new JEM-2010FEF

The new JEM-2010FEF electron microscope provides useful techniques based on energy filtering as an omega-type energy filter is integrated into a thermal field-emission 200 kV transmission electron microscope. For example, the zero-loss imaging improves the contrast of high resolution lattice images as well as images of precipitates or lattice defects in alloys. The acquisition time for elemental mapping with core-loss electrons is one order in magnitude shorter than with energy-dispersive X-ray spectroscopy. The removal of inelastically scattered electrons enables us to observe weak lines in convergent-beam electron diffraction patterns from a thicker specimen with a probe size 1–2 nm in diameter. A combination of the field emission gun and sensitive recording media such as an imaging plate and a slow-scan CCD camera makes the energy filtering more powerful.     

Automated microscopy for electron tomography.

Instrumentation and methodology for the automatic collection of tomographic tilt series data for the three-dimensional reconstruction of single particles is described. The system consists of a Philips EM 430 TEM, with a Gatan 673 cooled slow-scan CCD camera and a Philips C400 microscope computer control unit attached. The procedure for data collection includes direct digital recording of the images on the CCD camera and the automatic measurement and correction of (a) image shifts resulting from tilting the specimen, (b) variation of defocus and (c) the eucentric height position of the specimen. Experiments are described illustrating the possibilities and limitations of automatic data collection. Data collection at a magnification of 30k shows that the exposure time of the specimen to the beam is reduced by a factor of 10-100 compared to manual operation of the TEM.     

面阵CCD KAI-0340DM高速相机的设计

使用常规CCD设计了高速相机系统,并解决了相机高速工作方式下的一系列难题.介绍了行间转移面阵CCD芯片KAI-0340DM的工作原理,采用高度集成视频处理芯片来产生各高速时序信号;通过提高驱动芯片与线路板的热传导效率增加有效散热面积从而降低芯片的温升;建立了高速运放电路的自激振荡模型,并采用有效方法克服了自激振荡;采用...     

Scanning image detection (SID) system for conventional transmission electron microscope (CTEM) images

A new image detection system has been developed to display transmission electron microscope (TEM) images on a CRT without a video camera system. Deflection coils placed in both the upper space of an objective lens and in the lower space of the first intermediate lens scan a small electron probe simultaneously. The electrical signal acquired through an improved scintillator and a photomultiplier is synchronized with the scanning signal and displayed in a similar fashion to a conventional scanning TEM (STEM) instrument. A preliminary system using a 100 kV conventional TEM (CTEM) equipped with a hairpin-type electron gun, produced an image with a spatial resolution of 1 nm.     

Nanosecond time-resolved investigations using the in situ of dynamic transmission electron microscope (DTEM)

Most biological processes, chemical reactions and materials dynamics occur at rates much faster than can be captured with standard video rate acquisition methods in transmission electron microscopes (TEM). Thus, there is a need to increase the temporal resolution in order to capture and understand salient features of these rapid materials processes. This paper details the development of a high-time resolution dynamic transmission electron microscope (DTEM) that captures dynamics in materials with nanosecond time resolution. The current DTEM performance, having a spatial resolution <10nm for single-shot imaging using 15ns electron pulses, will be discussed in the context of experimental investigations in solid state reactions of NiAl reactive multilayer films, the study of martensitic transformations in nanocrystalline Ti and the catalytic growth of Si nanowires. In addition, this paper will address the technical issues involved with high current, electron pulse operation and the near-term improvements to the electron optics, which will greatly improve the signal and spatial resolutions, and to the laser system, which will allow tailored specimen and photocathode drive conditions.