Highly sensitive electron detector for electron energy loss spectroscopy and zero-loss filtered ptychography

2019年11月，柏林洪堡大学的IRIS Adlershof收到了一台配备单色仪和电子能量损失谱仪（EELS）系统的像差校正扫描透射电子显微镜（STEM）。该仪器将用于表征各种材料系统，包括CRC 951“光电混合无机/有机系统”（HIOS）中合作伙伴生产的样品，但也用于开发新的表征技术。该显微镜的特殊功能包括其高空间分辨率（< 0.07 nm）和EELS中的高光谱分辨率（< 6 meV），使其在德国独一无二。EELS光谱目前使用相机获取，其中落在一个像素中的电子也将在相邻像素中产生显著信号（差的点扩散函数）。这导致所记录的光谱的模糊，特别是当在强得多的峰附近记录非常弱的峰时。当通过低损耗EELS表征光束敏感有机材料时，通常是这种情况，其中一些振动峰非常接近强零损耗峰。在订购新的显微镜显微镜一年多后，直接电子探测器可用于其光谱仪。使用该检测器，可以在没有读出噪声和> 10 Mio：1的动态范围的情况下以至少2250帧每秒的帧速率记录衍射图案和EELS光谱，即，有效地比使用当前检测器高100倍以上。它可以同时记录超过10 Mio计数的零损耗峰值，同时仍然能够计数单个电子。因此，这种探测器极大地提高了记录数据的质量，并允许用于表征束敏感材料的电子剂量显着减少。使用这种显微镜进行的重叠关联实验也将大大受益于这种新探测器的增强速度和灵敏度。灵敏度的增强已经被证明允许重叠关联重建的空间分辨率的显著增加，至少对于非常薄的材料。

In November 2019, IRIS Adlershof of Humboldt University of Berlin received an aberration-corrected scanning transmission electron microscope (STEM) equipped with a monochromator and electron energy loss spectrometer (EELS) system. This instrument will be utilized to characterize a large variety of materials systems, including samples produced by partners within the CRC 951 "Hybrid Inorganic/Organic Systems for Opto-Electronics" (HIOS), but also to develop new characterization techniques. The special features of this microscope include its high spatial resolution (< 0.07 nm) and its high spectral resolution in EELS (< 6 meV), making it unique in Germany. EELS spectra are currently acquired using a camera in which electrons landing in one pixel will also generate significant signal in the neighboring pixels (poor point spread function). This leads to a smearing out of the recorded spectra, especially when very weak peaks are being recorded in the vicinity of much stronger peaks. This is commonly the case when characterizing beam-sensitive organic materials by low-loss EELS, where some vibrational peaks are very close to the strong zero-loss peak. More than one year after ordering the new microscope microscope, a direct electron detector became available for its spectrometer. With this detector diffraction patterns and EELS spectra can be recorded without read-out noise and a dynamic range of > 10 Mio : 1 at a frame rate of at least 2250 frames per second, i.e. effectively more than 100 times higher than with the current detector. It can simultaneously record a zero-loss peak with more than 10 Mio counts while still being able to count individual electrons. This detector thus enormously increases the quality of the recorded data and allows the electron dose for the characterization of beam-sensitive materials to be reduced significantly. The ptychography experiments being carried out using this microscope will also benefit greatly from the enhanced speed and sensitivity of this new detector. The enhancement in sensitivity has already been shown to allow for a significant increase in the spatial resolution of ptychography reconstructions, at least for very thin materials.