Enhancement of resolution and precision of TEM imaging by scanning illumination

在透射电子显微镜（TEM）中，主要分为两种成像模式：常规透射电子显微镜（CTEM）和扫描透射电子显微镜（STEM），前者使用平面相干电子波照射样品，后者使用电子束扫描样品并通过检测器记录散射电子。CTEM具有直接成像的优点，不受电子束定位误差的影响。相比之下，由于STEM是一种非相干成像模式，因此图像的解译更容易，空间分辨率也更好。我们在《物理学》上发表的一篇文章中证明了这一点。启。通过实验和仿真表明，将扫描照明应用于CTEM成像模式的新型成像模式系统（imaging STEM）结合了CTEM和STEM的优点。它提供比CTEM更好的空间分辨率，更容易解释对比模式，并且没有电子束定位误差的影响。然而，系统的优点也伴随着难以实现的缺点。该项目的第一个目标是通过编写操作和调整显微镜的专用脚本以及减少样品污染来提高系统的适用性。此外，迄今为止仅通过模拟显示的系统成像的优势将在实验中得到证明。这些优点包括测量原子柱位置的精度更高，以及在重原子柱直接附近对轻原子柱成像的突出可能性。在澳大利亚教授L. Allen等人最近发表的一篇文章中，建议通过减少伪影的能量滤波成像应用系统进行元素分析。这一方法将与ER-C j<s:1> lich合作进行测试。系统成像的优势将通过与高度热门问题相关的技术相关材料系统来展示。原子柱位置测量精度的提高将应用于仅几纳米厚的铁电隧道势垒的极化域测量，这些势垒有可能应用于存储器件。特别是，我们计划利用原位外加电场来研究这些势垒的开关行为。此外，系统成像光原子柱的可能性将被应用于测量氧八面体在不同钙钛矿材料之间的界面上的倾斜度。进一步的应用是测量可以应用于二氧化氮传感器的纳米线中晶格平面的自发起皱，以及研究纳米孔金表面附近的晶格应变，这影响了该材料体系的催化活性。

In transmission electron microscopy (TEM), mainly two imaging modes are differentiated: Conventional TEM (CTEM), which uses a plane coherent electron wave to illuminate the specimen, and scanning TEM (STEM), where the electron beam is scanned over the specimen and scattered electrons are registered by a detector. CTEM has the advantage of direct imaging which is not influenced by errors of positioning the electron beam. In contrast, as STEM is an incoherent imaging mode, the interpretation of images is easier and it provides a better spatial resolution.We were able to demonstrate in an article published in Phys. Rev. Lett. by experiment and simulation that the new imaging mode ISTEM (imaging STEM), which applies scanning illumination in the CTEM imaging mode, combines advantages of CTEM and STEM. It provides better spatial resolution than CTEM, interpretation of contrast patterns is easier and there is no influence of errors in positioning the electron beam. However, the advantages of ISTEM are accompanied by the disadvantage of a more difficult practicability. A first goal of the project is to improve the applicability of ISTEM by writing dedicated scripts to operate and adjust the microscope as well as reducing the contamination of the sample. In addition, advantages of ISTEM imaging that have only been shown by simulation so far will be demonstrated experimentally. These advantages include the higher precision of measuring the positions of atom columns, as well as the outstanding possibilities to image light atom columns in direct vicinity of heavy atom columns. In a recent publication of Prof. L. Allen et al. in Australia it was suggested to apply ISTEM for elemental analysis by energy filtered imaging with reduced artifacts. This approach will be tested in cooperation with the ER-C Jülich.The advantages of ISTEM imaging will be demonstrated using technologically relevant material systems that are connected with highly topical problems. The improved precision of the measurement of atom column positions will be applied to measure polarization domains in only a few nanometers thick ferroelectric tunnel barriers which are potential candidates for application in memory devices. Particularly, we plan to investigate the switching behavior of these barriers using in-situ applied electric fields. In addition, the possibilities of ISTEM to image light atom columns will be applied to measure tilts of oxygen-octahedra across the interfaces between different perovskite materials. Further applications are the measurement of spontaneous wrinkling of lattice planes in Te nanowires which can be applied in NO2 sensors, as well as the investigation of lattice strain close to the surface of nanoporous gold, which influences the catalytic activity of this material system.