Electron Microscopy of Structure and Spin Textures at Record Resolution
speaker: 陈震 康奈尔大学(美国)
place: 北京大学综合科研楼137会议室
time: 2020年1月6日(周一)上午10:00



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 ? in 2D materials [1]. I will demonstrate the unique capability of micron down to sub-angstrom length-scale imaging in Moiré-lattice of twisted bilayer transition metal dichalcogenides [2]. 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.