STEM imaging is typically performed by raster scanning a focused electron probe over a sample. Here we investigate and compare three different scan patterns, making use of a programmable scan engine that allows to arbitrarily set the sequence of probe positions that are consecutively visited on the sample. We compare the typical raster scan with a so-called 'snake' pattern where the scan direction is reversed after each row and a novel Hilbert scan pattern that changes scan direction rapidly and provides an homogeneous treatment of both scan directions. We experimentally evaluate the imaging performance on a single crystal test sample by varying dwell time and evaluating behaviour with respect to sample drift. We demonstrate the ability of the Hilbert scan pattern to more faithfully represent the high frequency content of the image in the presence of sample drift. It is also shown that Hilbert scanning provides reduced bias when measuring lattice parameters from the obtained scanned images while maintaining similar precision in both scan directions which is especially important when e.g. performing strain analysis. Compared to raster scanning with flyback correction, both snake and Hilbert scanning benefit from dose reduction as only small probe movement steps occur.

中文翻译：

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STEM 成像不同矩形扫描策略的评估

STEM 成像通常通过对样品进行光栅扫描聚焦电子探针来执行。在这里，我们研究并比较了三种不同的扫描模式，利用可编程扫描引擎，允许任意设置在样本上连续访问的探针位置序列。我们将典型的光栅扫描与所谓的“蛇形”模式（其中扫描方向在每行之后反转）和快速改变扫描方向并提供两个扫描方向的均匀处理的新型希尔伯特扫描模式进行比较。我们通过改变停留时间和评估样品漂移的行为来实验评估单晶测试样品的成像性能。我们展示了希尔伯特扫描模式在样本漂移存在的情况下更忠实地表示图像高频内容的能力。还表明，当从获得的扫描图像测量晶格参数时，希尔伯特扫描提供减少的偏差，同时在两个扫描方向上保持相似的精度，这在例如执行应变分析时尤其重要。与使用回扫校正的光栅扫描相比，蛇形扫描和希尔伯特扫描都受益于剂量减少，因为只发生很小的探针移动步骤。