Defect-induced Surface and Interface Reconstruction in Novel Two-dimensional Materials Revealed by Low Voltage Scanning Transmission Electron Microscopy

Two-dimensional (2D) materials attracted substantial attention due to their extraordinary physical properties resulting from the unique atomic thickness. 2D materials could be considered as material systems with flat surfaces at both sides, while the van der Waals gap is a natural out-of-plane interface between two monolayers. However, defects are inevitably presented and often cause significant surface and interface reconstruction, which modify the physical properties of the materials being investigated. In this review article, we reviewed the effort achieved in probing the defect structures and the reconstruction of surface and interface in novel 2D materials through aberration corrected low voltage scanning transmission electron microscopy (LVSTEM). The LVSTEM technique enables us to unveil the intrinsic atomic structure of defects atom-by-atom, and even directly visualize the dynamical reconstruction process with single atom precision. The effort in understanding the defect structures and their contributions in the surface and interface reconstructions in 2D materials shed light on the origin of their novel physical phenomenon, and also pave the way for defect engineering in future potential applications.