Controllable Growth Of Hexagonal Boron Nitride/Graphene Heterostructures

Graphene,the two-dimensional(2D)hexagonal honeycomb with sp2-hybridized carbon atoms,has great potential in the broad application of transparent conductive film,field effect transistor,sensor,energy storage materials due to its excellent physical and chemical properties.Beyond graphene,a series of other two-dimensional materials(2DMs)including hexagonal boron nitride(h-BN),transition metal sulfide(MoS2,WS2)have been discovered later on.Among all 2DMs,h-BN has attracted intense research interests owing to its unique atomic structure and the outstanding properties such as wide bandgap,low dielectric constant,high mechanical strength and so on.Especially,the stacking of h-BN and graphene films to form the vertical graphene/h-BN heterostructure has shown the novel characteristic of the photoinduced doping,the emergence of new Dirac points and the Hoffstadt butterfly,which broaden the application of graphene in optoelectronics and other fields.Chemical vapor deposition(CVD)has been a great success in the preparation of large-scale and high-quality graphene film,and has been widely applied in the synthesis of other 2DMs.However,the synthesis of heterostructure usually consists of two or more types of 2DMs which raise more difficulties in the growth control than one single material.Therefore,it is a urgent need to develop the novel approach to prepare large-area,high-quality heterostructure film with controllable thickness for further applications.Moreover,the 2DMs grown by CVD are typically polycrystalline,and the grain boundaries are expected to degrade the electrical and thermal properties of the resulting films.Therefore,the effective identification of grain boundaries is crucial to enabling the diverse application of 2DMs.The growth mechanism of graphene and h-BN synthesis on the high carbon-solubility metal substrate platinum has been studied seperately.Combing with the precipitation growth of graphene layer and the surface deposition growth of h-BN film,a direct synthesis of the high-quality h-BN/graphene heterostructure on platinum substrate via a two-step process was proposed.Due to the different growth mechanism,the thickness of graphene and h-BN layer in the heterostructure could be tuned separately.The carrier mobility of graphene measured on the h-BN can achieve as high as 10,000 cm2/V-s.The study of graphene grains and their boundary is critical for enabling diverse applications.In this work,thermal treatment in the atmospheric environment has been applied to introduce defects on the transferred graphene films.It is found that the intensity of Raman D peak at the edge of graphene and the grain boundary are significantly enhanced after heat treatment in air,whereas no change was found in D peak within the graphene grain.Therefore,the grain boundary distribution of the graphene films can be characterized by thermal treatment combined with Raman spectroscopy-scanning technique,which provides a rapid and effective method to identify the graphene grains on arbitrary substrates.