Enhancement of resolution and precision of TEM imaging by scanning illumination

在透射电子显微镜中，主要分为两种成像模式：常规电子显微镜(CTEM)和扫描电子显微镜(STEM)，前者使用平面相干电子波照射样品，后者将电子束扫描到样品上方，并由探测器记录散射电子。CTEM具有成像直接，不受电子束定位误差影响的优点。相比之下，由于STEM是一种非相干成像模式，图像的解释更容易，而且它提供了更好的空间分辨率。我们在发表在Phys上的一篇文章中进行了演示。莱特牧师。通过实验和仿真表明，在CTEM成像模式中采用扫描照明的新成像模式ISTEM(Imaging STEM)结合了CTEM和STEM的优点。它提供了比CTEM更好的空间分辨率，更容易解释对比图，并且不受电子束定位误差的影响。然而，ISTM的优点伴随着更难实用化的缺点。该项目的第一个目标是通过编写专门的脚本来操作和调整显微镜，并减少样品的污染，从而提高ISTEM的适用性。此外，到目前为止还只有通过模拟才能证明ISTEM成像的优点将在实验中得到证明。这些优势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.Allen等人最近发表的一篇文章中。在澳大利亚，建议使用ISTEM进行元素分析，通过减少伪影的能量过滤成像进行元素分析。这一方法将与ER-C Jülich合作进行测试。ISTEM成像的优势将使用与高度热门的问题有关的技术相关材料系统来演示。原子柱位置测量精度的提高将被应用于仅在几纳米厚的铁电隧道势垒中测量偏振域，这是潜在的应用于存储器件的候选。特别是，我们计划利用现场外加电场来研究这些势垒的开关行为。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的氧-八面体的倾斜度。进一步的应用包括测量Te纳米线中可用于NO2传感器的晶格面的自发起皱，以及研究影响该材料体系催化活性的纳米孔金表面附近的晶格应变。

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.