Institute of Physics, Laboratory for Ultrafast Microscopy and Electron Scattering (LUMES), École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland;
National Graphene Institute, University of Manchester, M13 9PL Manchester, United Kingdom.
Proc Natl Acad Sci U S A. 2018 Jul 17;115(29):7473-7478. doi: 10.1073/pnas.1722523115. Epub 2018 Jul 3.
The van der Waals heterostructures, which explore the synergetic properties of 2D materials when assembled into 3D stacks, have already brought to life a number of exciting phenomena and electronic devices. Still, the interaction between the layers in such assembly, possible surface reconstruction, and intrinsic and extrinsic defects are very difficult to characterize by any method, because of the single-atomic nature of the crystals involved. Here we present a convergent beam electron holographic technique which allows imaging of the stacking order in such heterostructures. Based on the interference of electron waves scattered on different crystals in the stack, this approach allows one to reconstruct the relative rotation, stretching, and out-of-plane corrugation of the layers with atomic precision. Being holographic in nature, our approach allows extraction of quantitative information about the 3D structure of the typical defects from a single image covering thousands of square nanometers. Furthermore, qualitative information about the defects in the stack can be extracted from the convergent diffraction patterns even without reconstruction, simply by comparing the patterns in different diffraction spots. We expect that convergent beam electron holography will be widely used to study the properties of van der Waals heterostructures.
范德瓦尔斯异质结构通过将二维材料组装成三维堆叠来探索它们的协同特性，已经带来了许多令人兴奋的现象和电子设备。尽管如此，由于所涉及晶体的单原子性质，这种组装中各层之间的相互作用、可能的表面重构以及固有和外在缺陷仍然很难用任何方法来表征。在这里，我们提出了一种会聚束电子全息技术，该技术允许对这种异质结构中的堆叠顺序进行成像。基于在堆叠中的不同晶体上散射的电子波的干涉，这种方法允许以原子精度重建层的相对旋转、拉伸和离面波纹。由于其全息性质，我们的方法允许从单个覆盖数千平方纳米的图像中提取关于典型缺陷的三维结构的定量信息。此外，甚至无需重建，仅通过比较不同衍射点的图案，就可以从会聚衍射图案中提取有关堆叠中缺陷的定性信息。我们预计会聚束电子全息术将被广泛用于研究范德瓦尔斯异质结构的性质。
