The Fabrication,characterization And Electronic Structure Of Graphene/hBN Van Der Waals Heterostructure

Two dimensional Van de Waals heterostructures have attracted numerous interests in both fondamental physics and practical applications.Different 2D materials will be held together by Van de Waals force if they are stacked one by one in vertical direction,forming Van de Waals heterostructures.This new kind of artifical structure usually shows unusual properties and new phenomena due to the synergetic effects,which offers us a platform to design various new devices.Here we focus on graphene/h BN Van de Waals heterostructure,one typical member of the famliy of two dimensional heterostructures.1.The eletronic structure of epitaxial grahpene/h BN heterostructure.We directly grow single-crystalline graphene on h BN.As grown graphene/h BN heterostructure shows trigonal moire patterns,which will fold the band structrue of graphene.We investigated the electronic structure of as grown graphene moire superlattice using both transport and ARPES techniques.We directly observed the second generation of Dirac points(superlattice Dirac points)locating at three K points of the superlattice Brillouin zone and only at one of the two superlattice valleys.A gap of ~160me V was also observed at origional Dirac point,indicating the strong inversion symmetry breaking in this system.Moreover,third generation of Dirac points were also observed unexpectly at higher doping level.It exhibited anomalous behavior in magntic field.2.Transprot measurements of graphene Corbino devices.Unlike typical two terminal devices,the edge current in Corbino devices does not contribute to conductance.The devices will exhibit metal-insulator transition when the Fermi surface is tuned across the Landau levels.We observed the gaps between different Landau levels in graphene Corbino devices.3.Growth and electronic transport studies on graphene nanoribbons.We have developed an approach to epitaxially grow graphene nanoribbons with controllable widths directly from the H-BN surface steps.Results show that suchgraphene nanoribbons also have superlattice structure.But unlike the 2D superlattice mentioned above,this superlattice is 1D.We fabricated field effect transistors based on such graphene nanoribbons and studied the transport properties.The preliminary results are very interesting,showing that the superlattice Dirac points can be shifted by the width of this 1D graphene superlattice.