Atom-by-atom structural and chemical analysis by annular dark-field electron microscopy
Atom-by-atom structural and chemical analysis by annular dark-field electron microscopy
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DOI：
10.1038/nature08879
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发表时间：
2010-03-25
期刊：
影响因子：
64.8
通讯作者：
Pennycook, Stephen J.
中科院分区：
文献类型：
--
作者：
Krivanek, Ondrej L.;Chisholm, Matthew F.;Pennycook, Stephen J.
对三维结构未知的材料中的所有原子进行直接成像和化学识别将构成一个非常强大的通用分析工具。正如包括费曼在内的许多科学家很早就意识到的那样，透射式电子显微镜原则上应该能够发挥这一作用。它用单个原子强烈散射的电子成像，这些电子的波长大约比原子小50倍。最近，由于引入了像差校正光学(2-8)，这项技术有了很大的进步。然而，无论是电子显微镜还是任何其他实验技术，都还没有能够分辨和识别由几个原子物种组成的非周期材料中的所有原子。在这里，我们展示了在优化的低电压工作的象差校正的扫描电子显微镜中的环形暗场成像可以分辨和识别单层六方氮化硼中包含替代缺陷的每个原子的化学类型。发现并鉴定了三种类型的原子取代：碳取代硼、碳取代氮和氧取代氮。这些取代在氮化硼单层中引起了约0.1埃量级的面内扭曲，直接解决了这一问题，并用密度泛函理论计算进行了验证。结果表明，对存在于超薄层及其上面的所有抗辐射损伤的原子进行逐个原子的结构和化学分析现在已经成为可能。
Direct imaging and chemical identification of all the atoms in a material with unknown three-dimensional structure would constitute a very powerful general analysis tool. Transmission electron microscopy should in principle be able to fulfil this role, as many scientists including Feynman realized early on(1). It images matter with electrons that scatter strongly from individual atoms and whose wavelengths are about 50 times smaller than an atom. Recently the technique has advanced greatly owing to the introduction of aberration-corrected optics(2-8). However, neither electron microscopy nor any other experimental technique has yet been able to resolve and identify all the atoms in a non-periodic material consisting of several atomic species. Here we show that annular dark-field imaging in an aberration-corrected scanning transmission electron microscope optimized for low voltage operation can resolve and identify the chemical type of every atom in monolayer hexagonal boron nitride that contains substitutional defects. Three types of atomic substitutions were found and identified: carbon substituting for boron, carbon substituting for nitrogen, and oxygen substituting for nitrogen. The substitutions caused in-plane distortions in the boron nitride monolayer of about 0.1 angstrom magnitude, which were directly resolved, and verified by density functional theory calculations. The results demonstrate that atom-by-atom structural and chemical analysis of all radiation-damage-resistant atoms present in, and on top of, ultrathin sheets has now become possible.