Fabrication And Characterization Of Graphene-Based Van Der Waals Heterostructures

The graphene-based van der Waals heterostructures have shown unique physical properties and possessed great potential in various applications.Based on an improved transfer method of graphene,this paper focuses on the controllable preparing and adjusting morphology of single-crystal graphene,as well as the growth and photoresponse of Molybdenum disulfide(MoS2)/graphene heterostructures.The main research results are listed here:The single-crystal graphene is grown by chemical vapor deposition using molybdenum sheets enclosed in copper pocket,which limits the internal carbon content.Under low pressure and high temperature conditions,methane is cracked into carbon atoms.Carbon atoms inside the copper box participate in two processes:some react with molybdenum metal as dissolved carbon,and the others are deposited on the surface of the copper foil to form graphene.The effects of growth temperature,annealing time,and gas flow on the growth are investigated.The grown graphene domains exist in different morphologies:dendritic and hexagonal.The growth parameters for hexagonal single-crystal graphene are optimized and successfully prepared high-quality hexagonal single-crystal graphene(HSCG)with size of nearly 100 μm.This provides a new avenue to grow single-crystal graphene.Furthermore,the MoS2/graphene heterostructures were prepared and their photoresponse was researched.The heterostructures were developed using a custom-designed high-vacuum vapor deposition system by directly growing MoS2 crystals on the surface of graphene.It is found that the growth of MoS2 on graphene follows a strict epitaxial growth mechanism,which can be used to mark the grain boundaries(GBs)of graphene.The G and 2D Raman bands of graphene show a blueshift after the growth of a single layer of MoS2.The photoluminescence(PL)quenching was observed for MoS2 grown on the surface of graphene.The PL peak at the GBs of MoS2/graphene shifts to a long wavelength.In addition,the photo current signal in MoS2/HSCG heterostructures is successfully captured without applying a bias.The photoresponse of the device is attributed to the optical absorption and response of MoS2 and the high carrier mobility of graphene.Through the direct preparation of MoS2/graphene heterostructures,the marking of graphene GBs and the preparation of high photoresponse devices are realized at the same time.These findings offer a new approach to develop optoelectronic devices based on two-dimensional material hetero structures.