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Real-space charge-density imaging with sub-angstroem resolution by four-dimensional electron microscopy

机译：二维电子显微镜在亚锥角分辨率下的实空间电荷密度成像

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摘要

The distribution of charge density in materials dictates their chemical bonding, electronic transport, and optical and mechanical properties. Indirectly measuring the charge density of bulk materials is possible through X-ray or electron diffraction techniques by fitting their structure factors(1-3), but only if the sample is perfectly homogeneous within the area illuminated by the beam. Meanwhile, scanning tunnelling microscopy and atomic force microscopy enable us to see chemical bonds, but only on the surface(4-6). It remains a challenge to resolve charge density in nanostructures and functional materials with imperfect crystalline structures-such as those with defects, interfaces or boundaries at which new physics emerges. Here we describe the development of a real-space imaging technique that can directly map the local charge density of crystalline materials with sub-angstrom resolution, using scanning transmission electron microscopy alongside an angle-resolved pixellated fast-electron detector. Using this technique, we image the interfacial charge distribution and ferroelectric polarization in a SrTiO3/BiFeO3 heterojunction in four dimensions, and discover charge accumulation at the interface that is induced by the penetration of the polarization field of BiFeO3. We validate this finding through side-by-side comparison with density functional theory calculations. Our charge-density imaging method advances electron microscopy from detecting atoms to imaging electron distributions, providing a new way of studying local bonding in crystalline solids.
机译：材料中电荷密度的分布决定了它们的化学键，电子传输以及光学和机械性能。可以通过X射线或电子衍射技术通过拟合结构因子来间接测量散装材料的电荷密度（1-3），但前提是样品在光束照射的区域内是完全均匀的。同时，扫描隧道显微镜和原子力显微镜使我们能够看到化学键，但仅在表面上（4-6）。解决具有不完善的晶体结构的纳米结构和功能材料中的电荷密度仍然是一个挑战，例如具有新物理出现的缺陷，界面或边界的结构。在这里，我们描述了一种实时空间成像技术的发展，该技术可以使用扫描透射电子显微镜和角度分辨像素化快速电子检测器，直接以亚埃分辨率绘制晶体材料的局部电荷密度。使用该技术，我们在四个维度上成像了SrTiO3 / BiFeO3异质结中的界面电荷分布和铁电极化，并发现了由于BiFeO3极化场的穿透而在界面处产生的电荷积累。我们通过与密度泛函理论计算的并排比较来验证这一发现。我们的电荷密度成像方法将电子显微镜技术从检测原子发展为成像电子分布，为研究结晶固体中的局部键合提供了新途径。

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  • 来源
    《Nature》 |2019年第7783期|480-484|共5页
  • 作者

    Gao Wenpei; Addiego Christopher; Wang Hui; Yan Xingxu; Hou Yusheng; Ji Dianxiang; Heikes Colin; Zhang Yi; Li Linze; Huyan Huaixun; Blum Thomas; Aoki Toshihiro; Nie Yuefeng; Schlom Darrell G.; Wu Ruqian; Pan Xiaoqing;

  • 作者单位

    Univ Calif Irvine Dept Mat Sci & Engn Irvine CA 92697 USA;

    Univ Calif Irvine Dept Phys & Astron Irvine CA 92697 USA;

    Univ Calif Irvine Dept Phys & Astron Irvine CA 92697 USA|Cent S Univ Sch Phys & Elect Hunan Key Lab Super Microstruct & Ultrafast Proc Changsha Hunan Peoples R China;

    Nanjing Univ Coll Engn & Appl Sci Collaborat Innovat Ctr Adv Microstruct Natl Lab Solid State Microstruct Nanjing Jiangsu Peoples R China;

    Cornell Univ Dept Mat Sci & Engn Ithaca NY 14853 USA;

    Univ Calif Irvine Irvine Mat Res Inst Irvine CA 92697 USA;

    Cornell Univ Dept Mat Sci & Engn Ithaca NY 14853 USA|Cornell Univ Kavli Inst Cornell Nanoscale Sci Ithaca NY USA;

    Univ Calif Irvine Dept Mat Sci & Engn Irvine CA 92697 USA|Univ Calif Irvine Dept Phys & Astron Irvine CA 92697 USA|Univ Calif Irvine Irvine Mat Res Inst Irvine CA 92697 USA;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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