Development of a specimen holder for in situ generation of pure in-plane magnetic fields in a transmission electron microscope

As the development of quantised storage media progresses, detailed knowledge is required about the magnetisation reversal behaviour of sub-micron sized magnetic structures in external magnetic fields. Using the Lorentz mode of transmission electron microscopy (LTEM) the magnetic microstructure of thin film samples can be imaged with high spatial resolution. A novel approach for in situ magnetising experiments is described which combines the development of a custom-made sample holder which generates two orthogonal in-plane components of magnetic field in the specimen plane with the benefit of computer-controlled variation of the field. We present a specimen stage suitable for a Philips CM30 Twin/LTEM, which allows the generation of well-defined magnetic in-plane fields in the TEM.     

In situ transmission electron microscopy studies and real-time digital imaging

A newly designed CCD camera has been utilized for real-time and static image acquisitions. The performance of the camera is demonstrated for heating/cooling in-situ TEM experiments performed on a commercial high strength aluminium alloy using a double tilt heating holder. The real-time digital imaging capability of the new camera should facilitate the in-situ TEM that is now re-establishing itself as a strategic tool for materials characterization.     

A charge coupled device camera with electron decelerator for intermediate voltage electron microscopy

Electron microscopists are increasingly turning to intermediate voltage electron microscopes (IVEMs) operating at 300-400 kV for a wide range of studies. They are also increasingly taking advantage of slow-scan charge coupled device (CCD) cameras, which have become widely used on electron microscopes. Under some conditions, CCDs provide an improvement in data quality over photographic film, as well as the many advantages of direct digital readout. However, CCD performance is seriously degraded on IVEMs compared to the more conventional 100 kV microscopes. In order to increase the efficiency and quality of data recording on IVEMs, we have developed a CCD camera system in which the electrons are decelerated to below 100 kV before impacting the camera, resulting in greatly improved performance in both signal quality and resolution compared to other CCDs used in electron microscopy. These improvements will allow high-quality image and diffraction data to be collected directly with the CCD, enabling improvements in data collection for applications including high-resolution electron crystallography, single particle reconstruction of protein structures, tomographic studies of cell ultrastructure, and remote microscope operation. This approach will enable us to use even larger format CCD chips that are being developed with smaller pixels.     

增量式光栅尺指示光栅自动粘接系统的设计

增量式光栅尺指示光栅粘接设备制造困难,精度较低,并且采用人眼观察手工调整的粘接方式,成品率低,粘接一致性得不到保证。为了改进设备与粘接方式,研发出一套自动粘接系统。该系统提出简单易实现的悬空吸附式结构,利用CCD相机替代人眼观察莫尔条纹的变化,并根据CCD提供的图像数据自动调整指示光栅以使其满足技术指标,保证了粘接的一致性。最后给出自动粘接系统的详细设计方案。     

Time-resolved spectra of dense plasma focus using spectrometer, streak camera, and CCD combination

A time-resolving spectrographic instrument has been assembled with the primary components of a spectrometer, image-converting streak camera, and CCD recording camera, for the primary purpose of diagnosing highly dynamic plasmas. A collection lens defines the sampled region and couples light from the plasma into a step index, multimode fiber which leads to the spectrometer. The output spectrum is focused onto the photocathode of the streak camera, the output of which is proximity-coupled to the CCD. The spectrometer configuration is essentially Czerny-Turner, but off-the-shelf Nikon refraction lenses, rather than mirrors, are used for practicality and flexibility. Only recently assembled, the instrument requires significant refinement, but has now taken data on both bridge wire and dense plasma focus experiments.     

Polycrystal orientation maps from TEM

Determination of topography of crystallite orientations is an important technique of investigation of polycrystalline materials. A system for creating orientation maps using transmission electron microscope (TEM) Kikuchi patterns and Convergent beam electron diffraction patterns is presented. The orientation maps are obtained using a step-by-step beam scan on a computer-controlled TEM equipped with a CCD camera. At each step, acquired diffraction patterns are indexed and orientations are determined. Although, the approach used is similar to that applied in SEM/electron back scattered diffraction (EBSD) orientation imaging setups, the TEM-based system considerably differs from its SEM counterpart. The main differences appear due to specific features of TEM and SEM diffraction patterns. Also, the resulting maps are not equivalent. On these generated by TEM, the accuracy of orientation determination can be better than 0.1 degrees. The spatial resolution is estimated to be about 10nm. The latter feature makes the TEM orientation mapping system an important tool for studies at fine scale unreachable by SEM/EBSD systems. The automatic orientation mapping is expected to be a useful complement of the conventional TEM contrast images. The new technique will be essential for characterization of fine structure materials. To illustrate that, example maps of an aluminum sample produced by severe plastic deformation are included.     

Reliability of phases retrieved from 400-kV spot-scan images of purple membranes acquired on a slow-scan CCD camera

Glucose-embedded purple membranes were used as a test specimen to evaluate the reliability of phases retrieved from 400-kV spot-scan images acquired on a 1024 × 1024 slow-scan CCD camera. This specimen was chosen because it represents a broad class of low-contrast radiation-sensitive biological objects and its structure is well established. The amplitudes of computed reflections from these images were strongly damped by the modulation transfer function of the camera. Nevertheless, their phases on average were < 12° different from the reference data of Henderson et al . (1986), Ultramicroscopy , 19 , 147–178, up to 8.8 Å resolution, which corresponds to 0.8 of the Nyquist frequency of the camera.     

Quantitative analysis of image contrast in phase contrast STEM for low dose imaging

This work quantitatively evaluates the contrast in phase contrast images of thin vermiculite crystals recorded by TEM and aberration-corrected bright-field STEM. Specimen movement induced by electron irradiation remains a major problem limiting the phase contrast in TEM images of radiation-sensitive specimens. While spot scanning improves the contrast, it does not eliminate the problem. One possibility is to utilise aberration-corrected scanning transmission electron microscopy (STEM) with an Ångstrom-sized probe to illuminate the sample, and thus further reduce irradiation-induced specimen movement. Vermiculite is relatively radiation insensitive in TEM to electron fluences below 100,000 e⁻/Ų and this is likely to be similar for STEM although different damage mechanisms could occur. We compare the performance of a TEM with a thermally assisted field emission electron gun (FEG) and charge coupled device (CCD) image capture to the performance of STEMs with spherical aberration correction, cold field emission electron sources and photomultiplier tube image capture at a range of electron fluences and similar illumination areas. We show that the absolute contrast of the phase contrast images obtained by aberration-corrected STEM is better than that obtained by TEM. Although the STEM contrast is higher, the efficiency of collection of electrons in bright field STEM is still much less than that in bright field TEM (where for thin samples virtually all the electrons contribute to the image), and the SNR of equivalent STEM images is three times lower. This is better than expected, probably due to the absence of a frequency dependent modulation transfer function in the STEM detection system. With optimisation of the STEM bright field collection angles, the efficiency may approach that of bright field TEM, and if reductions in beam-induced specimen movement are found, STEM could surpass the overall performance of TEM.     

Microtomography from limited projections in conventional TEM for 3D reconstruction of an intact cell

It is possible to generate three-dimensional reconstructions of whole, non-sectioned biological cells in conventional TEM using an 80 kV tungsten source. A TEM specimen stage was modified to accommodate a precise single-axis tilting mechanism controlled by a digital stepping motor interfaced to a computer. For image collection, a video camera was optically coupled to the TEM phosphorescent screen, and the video image was digitized by a frame buffer interfaced to a computer. Specimen tilt and projection image collection were fully computer-automated. This microtomography system design could be readily adapted for most TEMs. Image reconstruction was achieved through computation on projection images from limited tilts; typically less than thirty projection images were needed for a coarse 3D reconstruction. The iterative reconstruction algorithm used certain statistical assumptions about the distribution of image gray values. Since microtomography was performed on non-sectioned whole mount cells viewed under an 80 kV electron beam, methods of embedment-free specimen preparation with chemical fixation and extraction were employed. These methods were utilized successfully to permit good image formation of the entire cell mitotic nucleus a few micrometers in thickness. The 3D reconstruction of a single kidney cell mitotic nucleus was carried out and shown to produce a reasonable microtomogram of gross features like the condensed chromosomes.     

电子倍增CCD星相机的设计

针对导航领域对星相机的性能要求,通过在星相机中应用新型的电子倍增CCD(EMCCD),设计一种探测能力强、数据更新快的成像系统。说明了EMCCD工作原理,分析了EMCCD信噪比,介绍了基于TC285电子倍增CCD的星相机的设计方案,给出了CCD驱动电路、视频信号处理电路以及时序控制器的设计。用模拟拍星实验和实际拍星实验验证了所设计的相机的性能,同时对相机的应用进行了初步分析。通过分析实验图像的信噪比说明了设计的星相机具备在积分时间8ms以内探测6等星的能力,且其图像数据更新频率可达10frame/s,满足用短积分时间进行快速星光成像的要求。     

高真空光刻样品CCD显微观察装置

介绍了利用光场控制中性原子束制作微细图形的基本原理。针对具体的实验系统 ,设计并建立了一套用于高真空系统中原子光刻样品的 CCD显微观察装置 ,该装置以CCD相机实时采样通过计算机自动图像处理直接显示和输出样品的微结构信息。与传统装置相比 ,该装置在实验初期摸索实验工艺参数方面具有非常重要的作用。     

Digitally collected cryo-electron micrographs for single particle reconstruction

Several advantages and disadvantages have been cited for image collection with a slow-scan CCD camera. Here we explore its use for cryo-EM single particle reconstruction and present two practical examples. The icosahedral adenovirus (Ad) type 2 ( approximately 150 MDa) was reconstructed from 396 particle images. The Fourier shell correlation (FSC) 0.5 threshold and the Fourier shell phase residual (FSPR) 45 degrees criterion yielded 17 AA resolution for the ordered viral capsid. Visual comparison with the filtered Ad2 crystallographic hexon confirmed a resolution range of 15-17 A. The asymmetric DNA-PKcs protein (470 kDa) was reconstructed from 9,473 particle images, using a previously published reconstruction based on class-sum images as an orientational search model [Chiu et al. (1998) J. Mol. Biol. 284:1075-1081]. FSC and FSPR methods yielded 17 A resolution for the new DNA-PKcs reconstruction, indicating a small but noticeable improvement over that of the class-sum based reconstruction. Despite the lack of symmetry for DNA-PKcs and its lower image contrast compared to Ad2 (0.8% vs. 2.5%), the same resolution was obtained for both particles by averaging significantly more DNA-PKcs images. Use of the CCD camera enables the microscopist to adjust the electron beam strength interactively and thereby maximize the image contrast for beam sensitive samples. On-line Fourier transformation also allows routine monitoring of drift and astigmatism during image collection, resulting in a high percentage of micrographs suitable for image processing. In conclusion, our results show that digital image collection with the YAG-scintillator slow-scan CCD camera is a viable approach for 3D reconstruction of both symmetric and asymmetric particles.     

采用外触发方式实现CCD摄像机的全自动调光控制

针对传统的CCD摄像系统自动调光方法在工程使用中存在的不足,提出一种新型的CCD摄像系统的全自动调光方法。它采用外触发电子快门和可变光阑相组合进行调光,外触发电子快门调光为主,可变光阑调光为辅。采用外触发方式实现CCD摄像机的电子快门时间调节,由单片机控制电机调节可变光阑的通光口径,以使像面照度适中。反馈控制量由图像目标区域的均值电平获得,从而实现最佳全自动调光。简要叙述了新型调光系统的组成和工作原理。Matlab仿真结果表明,与传统调光方法相比,新型调光方法调光拍摄的图像对应的直方图分布更宽广且更均匀,功率谱幅值也更高,达到7.5dB以上。其图像更清晰,对比度更高,目标层次对比也更加明显,满足现代CCD摄像系统的最佳全自动调光要求。     

PW1410X射线荧光光谱仪的改造与应用

对荷兰飞利浦公司生产的ＰＷ１４１０Ｘ射线荧光光谱仪进行了改进，研制了专用的定性、定量分析接口板，将它们与ＩＢＭ－ＰＣ计算机样联；编制了通用的Ｘ射线荧光光谱定性和定量分析软件，使原先非自动化的仪器改造成可用ＩＢＭ－ＰＣ机进行分析数据自动化处理的更新仪器。     

“高分二号”上相机和星敏感器相对安装姿态的测量

为了精确测量"高分二号"(GF-2)卫星上相机和星敏感器的相对安装姿态,建立了一套高精度自动化测量系统。针对该系统研究了基于多传感器数据融合的高精度测量算法、基于理论安装数据驱动的自动测量模型、以及基于图像识别的立方镜法线搜索算法。该测量系统主要由二维龙门导轨、精密转台和CCD成像辅助准直的自准直经纬仪构成,通过融合精密转台的转动角度、自准直经纬仪的俯仰角和偏航角等数据计算被测设备安装姿态角度。测量时需先对系统进行标定,制定自动测量规划,然后通过电机驱动使设备自动到达预定位置和角度进行测量。若星上设备安装偏差较大导致被测对象超出自准直经纬仪测量范围时,可启动CCD相机对被测对象局部区域进行搜索识别,并引导自准直经纬仪实现精确准直测量。对测量系统进行了实验验证,结果显示:该系统姿态测量精度可以达到5″,与标准值比对最大偏差为4.1″;该测量系统已用于GF-2卫星的相机和星敏器相对姿态测量中,重复标准差最大为3.5″,满足GF-2对机上设备安装姿态测量精度的需求。     

A simple backscattered electrons and specimen current detection device for the scanning electron microscope

A simple, low-investment device has been developed that allows the collection of backscattered electrons (BSEs) and specimen current (SC) signals for imaging purposes and current measurement. Originally, this system was designed for detection, measurement, and display of specimen current, with a video signal output whose level was modulated by this current. Eventually, a BSE detector was developed, using a graphite disk (about 8 cm in diameter) to collect the BSEs. The disk was mounted on a Philips SEM 5O5, attached and concentrically to the final lens aperture. This configuration gives a large solid angle of collection. The collected charge is further processed by the same electronics used in the aforementioned SC detection system. Electron channeling, topographic contrast with BSE, and material contrast with BSE and SC images can be obtained with reasonably good edge definition.     

微小圆形物体几何参数自动测量仪

利用可反射和透射照明的正置金相显微镜对微小圆形物体进行放大,由摄象机接收放大后的图象。通过对图象的自动扫描和电子细分技术获取图象的边缘信息,用微机进行数据处理,计算所需的各种几何参数。     

指针式指示表自动检定仪的设计及应用

设计了一套基于图像识别的指针式指示表自动检定系统,该系统由CCD摄像头代替人眼采集指示表的图像,经过数学计算,得出指针在表盘上的示值,检定工作、数据处理均由计算机控制完成。测量实例说明该系统降低了操作人员的劳动强度及人为因素对检定精度的影响,具有准确性高、可靠性好、操作简方便、检定速度快等优点。     

适于高速CCD图像数据光纤传输的纠错技术

提出了一种适于高速CCD图像数据光纤传输的纠错算法用于提高大视场时间积分延迟(TDI)CCD相机中图像数据传输的可靠性。首先,分析了大视场空间相机图像数据光纤传输特点和光纤信道加性高斯白噪声(AWGN)模型下的数据传输差错,在此基础上提出了(16,8)纠错编码算法。阐述了(16,8)纠错编码算法思想以及纠错原理,说明了(16,8)纠错编码器的超大规模集成电路(VLSI)实现方法和编码器电路。然后,从不同角度分析了(16,8)纠错编码算法在大视场空间相机中应用的可行性。最后,在一空间多光谱相机样机的传输系统上进行了试验验证。结果表明:(16,8)纠错编码算法纠错能力强、易于硬件实现、占用资源少,在3 043Byte内可以纠正191bit错误,编码器资源占用率小于5%。提出的算法提高了空间相机中图像数据光纤传输的可靠性。