EXPERIMENTS WITH A HIGH RESOLUTION FIELD-EMISSION STEM

BEIP中电子能量损失(EELS)图的获取技术 场发射STEM得到了进一步的发展。计算机控制 对样品漂移的补偿已经实施，以允许长时间 检测所需的采集时间(超过两个小时) 冷冻组织中元素的生理浓度。这 补偿是通过定期收集快速弹性实现的 利用自动傅里叶互相关技术绘制鳗鱼地图期间的图像 方法来确定移位向量，然后应用这些移位向量来校正 漂移。还开发了一种新的光谱采集模式来 减少对射线敏感的生物样本的辐射损害。之后 获取快速数字弹性图像，待处理区域的二值化掩模 分析结果被生成并反馈到数字扫描生成器中。在……里面 这样，鳗鱼光谱就可以通过分发的方式以低剂量收集 任何扩展的样品区域上的入射电子 形状复杂。另一方面，鳗鱼与 数字暗视野成像已经被用来确定 蛋白质晶体，为了执行更精确的三维 电子结晶学，因此来自不同晶体的数据可以 已成功合并。

Techniques for acquiring electron energy loss (EELS) maps in the BEIP field-emission STEM have been developed further. Computer-controlled compensation for specimen drift has been implemented to allow the long acquisition times (in excess of two hours) required to detect physiological concentrations of elements in cryosectioned tissue. This compensation has been achieved by periodically collecting fast elastic images during EELS mapping and using automated Fourier cross-correlation methods to determine shift vectors, which are then applied to correct for the drift. A new spectral acquisition mode has also been developed to reduce radiation damage in beam-sensitive biological specimens. After acquiring a fast digital elastic image, a binary mask of the area to be analyzed is generated and fed back into the digital scan generator. In this way, the EELS spectrum can be collected at low dose by distributing the incident electrons over any extended specimen area that has a complicated shape. In another development, EELS in combination with digital dark-field imaging has been used to determine the thicknesses of protein crystals, in order to perform more accurate three-dimensional electron crystallography so that data from different crystals can be successfully merged.