Controllable preparation and photoelectric applications of two-dimensional in-plane and van der Waals heterostructures

<sec>Since the discovery of graphene, two-dimensional (2D) materials have received continuous attention and carried out in-depth exploration and development due to their excellent properties. With the exploration of the preparation of new 2D materials, one began to consider the synergistic effects produced by the in-plane junction and interlayer stacking to compensate for the defects of a single material and obtain some new properties. Matching the lattice structure to achieve specific functionalization, or using van der Waals force to achieve stacking, helps to introduce a new degree of freedom by combining different 2D materials, and open a new window for the research and practical application of 2D materials.</sec><sec>From the perspective of atomic manufacturing, in this article we introduce the controllable preparation and optoelectronic applications of 2D planar and van der Waals heterojunction materials. First, we briefly introduce the common 2D materials such as graphene, hexagonal boron nitride, transition metal dichalcogenides and black phosphorus used in the preparation of heterojunctions and related concepts of heterojunctions. Second, we review, in principle, the commonly used characterization methods including scanning probe-based techniques, spectrum-based, electron-based imaging techniques and others. Third, we summarize the preparation methods of planar and vertical heterojunctions. Basically, mechanical transfer method such as wet or dry method can be used to produce various vertical heterostructures of 2D materials, but usually lack the scalability. On the other hand, chemical vapor deposition method provides a scalable route to producing the planar heterostructure and vertical structure of 2D materials. Several strategies have been developed to produce various heterostructures. In addition, the recent development of twist-angle and quasi-crystalline bi-layer graphene is briefly reviewed. Fourth, the properties and applications of 2D van der Waals heterostructures such as field-effect transistor, light emitting diode, solar cell, flexible optoelectronic devices and plasmonic applications are introduced. Finally, the problems in the field are discussed, and the outlook is provided. </sec>