使用Timepix3探测器进行事件驱动的4D STEM采集：微秒停留时间和更快的扫描，适用于高精度和低剂量应用
Event driven 4D STEM acquisition with a Timepix3 detector: microsecond dwell time and faster scans for high precision and low dose applications
摘要：
四维扫描透射电子显微镜（4D STEM）非常详细地记录了材料中电子的散射。由4D STEM提供的益处是实质性的，其提供的丰富数据促进例如经由基于质心或重叠关联分析的高精度、高电子剂量效率相位成像。然而，在每个探头位置处记录散射的2D图像的要求长期以来对可以执行4D STEM的速度造成了严重的瓶颈。照相机技术的最新进展大大减少了这一瓶颈，直接电子探测器的探测效率特别适合该技术。然而，即使是最快的帧驱动像素化检测器仍然显著限制了可以在4D STEM中使用的扫描速度，使得所得到的数据容易漂移并阻碍其用于低剂量射束敏感应用。在这里，我们报告了使用事件驱动的Timepix 3直接电子相机的发展，使我们能够克服这一瓶颈，并实现4D STEM停留时间下降到100 ns;数量级快于基于帧的读出。我们对不同加速电压的检测器进行了测试，并表明该方法特别适合于低剂量成像，并且与传统的STEM成像相比，在不影响停留时间的情况下，可以提供丰富的数据集。
英文摘要：
Four dimensional scanning transmission electron microscopy (4D STEM) records the scattering of electrons in a material in great detail. The benefits offered by 4D STEM are substantial, with the wealth of data it provides facilitating for instance high precision, high electron dose efficiency phase imaging via center of mass or ptychography based analysis. However the requirement for a 2D image of the scattering to be recorded at each probe position has long placed a severe bottleneck on the speed at which 4D STEM can be performed. Recent advances in camera technology have greatly reduced this bottleneck, with the detection efficiency of direct electron detectors being especially well suited to the technique. However even the fastest frame driven pixelated detectors still significantly limit the scan speed which can be used in 4D STEM, making the resulting data susceptible to drift and hampering its use for low dose beam sensitive applications. Here we report the development of the use of an event driven Timepix3 direct electron camera that allows us to overcome this bottleneck and achieve 4D STEM dwell times down to 100~ns; orders of magnitude faster than what has been possible with frame based readout. We characterise the detector for different acceleration voltages and show that the method is especially well suited for low dose imaging and promises rich datasets without compromising dwell time when compared to conventional STEM imaging.
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