Atomic Defects in Two-Dimensioal Materials: From Single-Atom Spectroscopy to Functionalities in Opto-/Electronics, Nanomagnetism, and Catalysis

Two-dimensional layered graphene-like crystals including transition metal dichalcogenides (TMDs) have received extensive research interest due to their diverse electronic, valleytronic and chemical properties, with the corresponding optoelectronics and catalysis application being actively explored. However, the recent surge in two-dimensional materials science is accompanied by equally great challenges such as defects engineering in the large-scale sample synthesis. It is necessary to elucidate the effect of structural defects on the electronic properties, in order to develop an application-specific strategy for the defect engineering. Here in this paper, we review the two aspects of the existing knowledge of native defects in two-dimensional crystals. One is the point defects emerging in graphene and hexagonal boron nitride as probed by atomically resolved electron microscopy and their local electronic properties as measured by single-atom electron energy-loss spectroscopy. The other will focus on the point defects in TMDs and their influence on the electronic structure, photoluminescence and electric transport properties. Our review of atomic defects in two-dimensional materials will offer a clear picture of the defect physics involved to demonstrate the local modulation of the electronic properties and possibly benefit in potential applications in magnetism and catalysis.