Controllable synthesis of two dimensional heterostructures and their application

Abstract

Since the successful exfoliation of graphene in 2004, many attentions have been paid to two-dimensional (2D) materials, which include graphene, h-BN, transition metal dichalcogenides (TMDCs), black phosphorus (BP) and so on. Although these materials have shown unique characteristics, there are numerous challenges in this emerging field. For example, charge trap between the substrate and the 2D materials seriously influences their excellent electrical properties; some 2D materials are unstable while exposed in air, which will lead to their degradation. To have an intensive study of the basic properties of 2D materials and broaden their field of application, researchers pay attentions to the heterostructures of these materials, which consist of vertically stacked or laterally pieced 2D materials, including graphene/h-BN, TMDCs/h-BN, TMDCs/graphene, and TMDCs/TMDCs heterostructures, et al. For vertical heterostructures, graphene/h- BN vertical heterostructures mainly take advantage of h-BN to decrease the charge trap between insulating layer and graphene, thus to increase the carrier mobility in graphene. TMDCs/graphene vertical heterostructures mainly combine the good photo responsivity of TMDCs with the high conductivity of graphene, which can be utilized for high performance optoelectronics. TMDCs/TMDCs vertical heterostructures mainly combine the band structures of two different materials to control the carrier transport behavior, thus realizing excellent carrier storage or high performance photo responsivity. Lateral heterostructures are only suitable for materials with low lattice mismatch, and they are usually used for studying the carrier transport behavior between the interfaces of materials. Along with the increasing requirements on integration and multifunction, 2D heterostructures-based electronic and optoelectronic devices are paid much more attention to. Controllable synthesis of 2D heterostructures is the precondition of constructions of high-performance and highly-integrated devices. This review first introduces the preparation methods of 2D materials, including exfoliation, molecular beam epitaxy (MBE) and chemical vapor deposition (CVD). Exfoliation method mainly pieces the exfoliated materials together to form heterostructures with the help of polymer. MBE can overcome the difficulties of the transfer process in exfoliation, however they are not suitable for large scale preparation. Compared with exfoliation and MBE, CVD has less restrictions on the substrate, as well as a simple preparation process with lower cost and higher quality of the as-prepared materials. 2D heterostructures can be prepared by the combination of exfoliation and CVD, or CVD process only. Then, considering the problem of the interface contamination in these preparation methods proposed at present, we put forward a liquid metal strategy in the controllable preparation of 2D heterostructures. Furthermore, we introduce the construction and performance of 2D-heterostructures-based electronic and optical devices. The opportunities and challenges in the preparation and application of 2D heterostructures are also discussed.