Enhancement of resolution and precision of TEM imaging by scanning illumination

在透射电子显微镜（TEM）中，主要有两种成像模式：常规TEM（CTEM），它使用平面相干电子波照射样品，和扫描TEM（STEM），其中电子束在样品上扫描，散射的电子由检测器记录。CTEM具有直接成像的优点，其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，因此图像的解释更容易，并且它提供了更好的空间分辨率。通过实验和仿真，提出了一种新的成像模式ISTEM（imagingSTEM），它将扫描照明应用于CTEM成像模式，结合了CTEM和STEM的优点。它提供了比CTEM更好的空间分辨率，对比度图案的解释更容易，并且在定位电子束时没有误差的影响。然而，ISTEM的优点伴随着更难实用的缺点。该项目的第一个目标是通过编写专用脚本来操作和调整显微镜以及减少样品的污染来提高ISTEM的适用性。 此外，ISTEM成像的优点，迄今为止只通过模拟显示，将实验证明。这些优点包括测量原子柱位置的更高精度，以及在重原子柱附近直接成像轻原子柱的突出可能性。在L.澳大利亚的艾伦等人建议通过减少伪影的能量过滤成像将ISTEM应用于元素分析。该方法将与ER-C Jülich合作进行测试。ISTEM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进行展示。原子柱位置的测量精度的提高将被施加到测量极化域在只有几个纳米厚的铁电隧道势垒，这是潜在的候选人在存储器设备中的应用。特别是，我们计划调查的开关行为，这些障碍使用原位施加电场。此外，ISTEM成像轻原子柱的可能性将被应用于测量不同钙钛矿材料之间界面上氧八面体的倾斜。进一步的应用是在Te纳米线，可应用于NO2传感器，以及靠近纳米多孔金的表面的晶格应变，这影响了该材料系统的催化活性的调查中的晶格平面的自发的双折射的测量。

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.