Study On The Controllable Preparation And Growth Mechanism Of Two-dimensional MoSe₂ Chemical Vapor Deposition

Since the discovery of graphene,two-dimensional(2D)materials have attracted great attention.MoSe₂and other transition metal disulfides(TMD)with a two-dimensional layered structure of atomic thickness have been widely studied due to their excellent electronic and optical properties.Single-layer MoSe₂has a direct band gap and can produce extremely high intensity photoluminescence(PL).When the thickness of MoSe₂crystal increases from single layer to multiple layer,its band structure can change from direct band gap to indirect band gap.This adjustable band gap provides a good prospect for the development of optoelectronic devices,valley electronics and spintronics.Although there are many ways to synthesize two-dimensional MoSe₂,it is still challenging to prepare large-area,high-quality,and morphologically controlled MoSe₂.At present,most studies on the growth of MoSe₂by CVD method are limited to the size of the growth size or the difference of the growth substrate,and the study on the growth mechanism still needs to be explored systematically.In this paper,two-dimensional MoSe₂films,arrays and dendrites were prepared by CVD under different conditions.The surface morphology,crystal structure and properties of MoSe₂with different morphologies were studied systematically,and the growth mechanism was investigated thoroughly.In this thesis,the main contents are as follows:(1)The research on the controllable preparation and growth mechanism of MoSe₂films with different layers in large area.A large-area,higher-quality MoSe₂thin film with different layers and monolayer size of 3 mm was prepared using the atmospheric pressure CVD method with only Ar gas assist.The effects of Mo source(Mo O₃film and Mo O₃powder)and Se powder temperature on the quality and crystallinity of MoSe₂film were studied.The optimal growth conditions of MoSe₂films with high crystal quality were obtained.The properties of large size,uniform surface continuity and high crystallinity of MoSe₂films grown by this method were proved by various characterization methods.In addition,the hydrodynamics boundary layer theory and diffusion theory of the wing model were used for the first time to study the growth mechanism of MoSe₂films with different layers.Our results provide reference value for CVD method to grow large-area,uniform,continuous and high-quality two-dimensional films,and this new theoretical model also expands our understanding of the growth mechanism of other two-dimensional materials.(2)The research on the controllable preparation of MoSe₂array and its growth mechanism.High quality triangular MoSe₂monocrystal,hexagon MoSe₂monocrystal and MoSe₂array were successfully prepared by atmospheric CVD method,and various characterization methods were used to prove that they all have good uniformity and crystallinity.The effects of different excitation wavelengths and array angles on Raman and PL spectra were studied.Finally,the growth mechanism of MoSe₂array is explained.Our experimental results provide reference value for the preparation of two-dimensional material arrays without templates.(3)The research on controlled preparation and growth mechanism of monolayer MoSe₂dendrites.Monolayer MoSe₂dendrites were successfully prepared by atmospheric CVD method.The effects of Se powder temperature and reaction temperature on MoSe₂dendrites were studied respectively.The optimal growth conditions of monolayer MoSe₂dendrites with high crystal quality were obtained.Various characterization methods were used to prove that the MoSe₂dendrites grown under this method had better uniformity and crystallinity,and the growth mechanism of MoSe₂dendrites was also clarified.Our experimental results provide reference value for the preparation of two-dimensional material dendrites.