EXPERIMENTS WITH A HIGH RESOLUTION FIELD-EMISSION STEM

BEIP中获取电子能量损失（EELS）图的技术 场发射STEM得到了进一步的发展。 计算机控制 补偿样品漂移已经实施，以允许长 检测所需的采集时间（超过两小时） 冷冻切片组织中元素的生理浓度。 这 通过周期性地收集快速弹性， 图像在EELS映射和使用自动傅立叶互相关 方法来确定移位向量，然后应用于校正 漂移 还开发了一种新的光谱采集模式， 减少对光束敏感的生物样本的辐射损伤。 后 获取快速数字弹性图像，待测量区域的二值掩模， 生成并反馈到数字扫描生成器中。 在 这样，EELS光谱可以通过分布在低剂量下收集， 入射电子在任何延伸的样品区域， 复杂的形状 在另一个发展中，EELS与 数字暗场成像已经被用于确定 蛋白质晶体，以执行更准确的三维 电子晶体学，以便从不同的晶体数据可以 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.