Epitaxial Growth Of Molybdenum Disulfide On Graphitic Substrates And The Properties Of Their Heterostructures

The discovery of graphene arouses great research interest into two-dimensional materials.Single-layer molybdenum disulfide(MoS2)has also attracted increasing attention in recent years.The heterostructures combined graphene and MoS2 exhibit unusual properties and novel phenomena due to their complementary advantages,which further widen the application of these two materials in micro-nano electronics and optoelectronics.The preparation and investigation of 2D heterostructures are in its infant stage so far,and the detailed understanding of their structure and properties is still lacking.In this thesis,we focus on the epitaxial growth and the structural properties of molybdenum disulfide on graphitic substrates.The heterostructures of graphene and MoS2 based on ZnO have been further prepared,in which the structural and optical properties have been investigated.The main results are as follows.The epitaxial growth of molybdenum disulfide on graphitic substrates has been studied firstly.Based on the optimization of experimental parameters,the single-layer molybdenum disulfide with high quality has been prepared by molecular beam epitaxy method in our lab-built vacuum system.The initial growth of MoS2 on the graphite surface has been studied by using scanning electron microscopy,Raman spectroscopy,and scanning tunneling microscopy.It is observed that molybdenum disulfide nucleates preferentially at the edge of the graphite steps to form monolayer triangular flakes,and follows the lattice orientation of the graphite substrate.A model of MoS2/graphite heterostructure has been established based on our experimental observations,and further investigated by using the first-principles calculations.The results show that the hybrid system exhibits semi-metallic properties,in which MoS2 and graphite retain their main characteristics of band structures due to the relatively weak interaction between them.On the other hand,the heterostructures of graphene and molybdenum disulfide on the basis of ZnO substrate have been successfully prepared by mechanical transfer and epitaxial growth.The interlayer interaction and optical properties have been investigated based on Raman and photoluminescence studies.It is found that the ultraviolet luminescence of zinc oxide is enhanced effectively in the heterostructures,which can be attributed to the exciton resonance at the interface.The results obtained here provide scientific data for the function expansion and performance improvement of two-dimensional materials such as graphene and molybdenum disulfide,as well as light emitting materials such as zinc oxide.