School of Applied and Engineering Physics, Cornell University
Scanning transmission electron microscopy (STEM) is known to be an atomic-resolution imaging technique for hard materials, such as ceramics or metals. However, high resolution imaging for beam sensitive materials, such as 2D and biological materials, is very challenging due to the electron-induced damage and the dose inefficiency of the conventional STEM imaging methods. New fast, high-dynamic-range pixel array detectors enable detection of all electrons with both momentum and position resolution, encoding all structural information of the sample. Utilizing a computational phase-contrast imaging technique, electron ptychography, we achieved a new spatial-resolution record of 0.39 Å in 2D materials . I will demonstrate the unique capability of micron down to sub-angstrom length-scale imaging in Moiré-lattice of twisted bilayer transition metal dichalcogenides . This new detector also allows analyses of strain in catalysts and local ordering in metallic glasses, and direct imaging of quantum states, such as polarization and spin textures. I will show spin textures imaging with magnetic-field sensitivity high enough for detecting magnetic domains in sub-nanometer thick ferromagnetic films at ~1 nm spatial resolution. We can determine the topological properties of skyrmions, such as singularities and chirality in both single crystal samples and embedded magnetic films. I will also show skyrmion nucleation with a sub-micron second electric current pulse in devices under electron microscope.
 Yi Jiang*, Zhen Chen*, et al., Nature 559, 343–349 (2018)
 Zhen Chen, et al., under review on Nature Communications (2019)
Zhen Chen is currently a Postdoctoral Associate in School of Applied and Engineering Physics at Cornell University. He obtained his PhD from the Institute of Physics, Chinese Academy of Sciences in 2014. After that, he went to Monash University in Australia as a Research Fellow working with Dr. Scott Findlay in 2014-2016. From 2016, he started working with Prof. David Muller at Cornell University in USA. His main research interests are developing new electron microscopy techniques for understanding atomic-scale structural and physical properties of materials. He was awarded Presidential Postdoctoral Award by Microscopy and Microanalysis Society of America in 2016 and 2018. He was also awarded for Microscopy Today Innovation Awards in 2019 as one of the developers of electron microscope pixel array detector. He serves as the referee for several renowned journals, such as Nature Communications, Physical Review Letters, Physical Review B, Applied Physics Letters and Microscopy & Microanalysis.
报告邀请人：李建奇 研究员 82649524，先进材料与结构分析实验室A06组