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有广泛的应用。它们提供了比照相胶片更快的图像和衍射数据，并且这种周转时间的改进使得标本评估、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CCD收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100 kV以上时，由于闪烁体的效率降低，CCD的性能严重受损。较高的电压导致信号电平降低和噪声的引入，以及电子在闪烁体内的横向散射增加，从而降低了分辨率。这些效应加在一起可以产生远低于胶片的探测量子效率（DQE），对于像蛋白质的低剂量成像这样的工作来说确实太低了。随着高加速电压的诸多优点被越来越多地认识到，工作在300 - 400kv的中压电子显微镜（ivem）的使用越来越多，因此这些显微镜的CCD性能越来越受到限制。我们正在建立一个新的CCD相机系统，旨在通过在电子到达相机之前减速来克服CCD相机在ivem上的不良性能。我们安装了CCD，使其可以漂浮到200千伏左右，因此，当显微镜在300千伏下工作时，我们获得了IVEM的优点，但相机应该在100千伏显微镜上表现良好。将进一步改进闪烁体，以产生比目前更好的信号和分辨率特性。这一进步将反过来使我们能够利用最新的、用更小像素制造的超大尺寸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等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.