CCD Camera for Intermediate Voltage Electron Microscopes

描述(申请人提供)：电荷耦合器件(CCD)相机在电子显微镜中得到了广泛的应用。它们提供比照相胶片快得多的图像和衍射数据，这种周转时间的改善使得样品评估、显微镜操作和自动化以及数据记录的效率得到了极大的提高。对于某些类型的工作，用电荷耦合器件采集的数据比用胶片记录的数据质量更高。然而，当显微镜工作在100kV以上时，由于闪烁体效率的降低，CCD的性能会受到严重的影响。较高的电压导致信号电平的降低和噪声的引入，以及闪烁体内电子横向散射的增加，从而降低了分辨率。这些效应加在一起可以产生远远低于胶片的探测量子效率(DQE)，对于蛋白质的低剂量成像等工作来说确实太低了。随着更高的加速电压的许多优点得到更广泛的认识，工作在300-400千伏的中压电子显微镜(IVEM)的使用越来越多，因此这些显微镜上的电荷耦合器件的性能越来越受到限制。我们正在建造一种新的ccd相机系统，旨在通过在电子到达相机之前对电子进行减速来克服iVEM上ccd相机性能差的问题。我们安装了电荷耦合器件，以便它可以漂浮到200千伏左右，因此当显微镜在300千伏时操作时，我们获得了IVEM的优点，但相机的性能应该与100千伏的显微镜一样好。将对闪烁体进行进一步改进，以产生比目前更好的信号和分辨率特性。反过来，这一进步将使我们能够利用最新的、非常大的、用更小像素制造的ccd。这些适应将在从蛋白质和病毒的高分辨率结构研究到细胞超微结构的三维研究的工作中产生实质性的好处。

DESCRIPTION (provided by applicant): Charge-coupled device (CCD) cameras have found wide application in electron microscopy. They provide much faster availability of image and diffraction data than photographic film, and this improvement in turnaround time has allowed a tremendous increase in the efficiency of specimen evaluation, microscope operation and automation, and data recording. For some types of work the data collected with a CCD is of higher quality than that recorded on film. However, the CCD performance is seriously compromised when the microscope is operated much above 100 kV, due to the decrease in efficiency of the scintillator. The higher voltages result in a decrease of the signal level and introduction of noise, as well as an increase in lateral scattering of the electrons within the scintillator, which decreases the resolution. Together these effects can produce a detective quantum efficiency (DQE) which is far below that of film, and indeed too low for work such as low-dose imaging of proteins. The use of Intermediate Voltage Electron Microscopes (IVEMs) operating at 300 - 400 kV is increasing as the many advantages of the higher accelerating voltage become more widely recognized, so the CCD performance on these microscopes is becoming more of a limitation. We are building a new CCD camera system designed to overcome the poor performance of CCD cameras on IVEMs by decelerating the electrons before they reach the camera. We mount the CCD so that it can be floated to around 200 kV, so that when the microscope is operated at 300 kV we obtain the advantages of the IVEM but the camera should perform as well as on a 100 kV microscope. Further improvements will be made to the scintillator to produce even better signal and resolution characteristics than currently available. This advance will, in turn, allow us to utilize the newest, very large format CCDs that are fabricated with smaller pixels. These adaptations will produce substantial benefits in work ranging from high-resolution structural studies of proteins and viruses to the three dimensional study of cell ultrastructure.