Preparation And Luminescence Of High Quality Single Layer Molybdenum Disulfide

In recent years,transition metal chalcogenides with the unique optical,electrical,valley electronics,and catalyst applications have attracted great interest from researchers.The structure of the transition metal chalcogenide is layered,similar to materials such as graphene,hexagonal boron nitride,and black phosphorus.A large number of basic researches on transition metal chalcogenides,especially heterojunctions,have greatly promoted the understanding of the properties of two-dimensional materials.As a member of the transition metal chalcogenide,molybdenum disulfide has attracted much attention due to its good chemical stability.The main content of this thesis is to propose two preparation methods of two-dimensional molybdenum disulfide.First,the metal molybdenum is used as a source to synthesize a single-layer,two-layer molybdenum disulfide with chemical vapor deposition technology.Second,a new "seed" tungsten trioxide is proposed to promote the synthesis of single-layer molybdenum disulfide.This method can increase the single crystal size of molybdenum disulfide and broaden the growth temperature of molybdenum disulfide.In the first chapter of this thesis,we introduce the structure of molybdenum disulfide in detail,including crystal structure,electronic structure,boundary structure and doping.The properties of single-layer molybdenum disulfide,including mechanical properties,thermal properties,optical properties,electrical properties and magnetic properties,are also presented.Finally,we illustrate the application prospects of two-dimensional molybdenum disulfide in optoelectronic devices,energy electronics,sensors and hydrogen production catalysis.In the second chapter of this thesis,we introduce the common preparation methods and corresponding characteristics of two-dimensional molybdenum disulfide,including mechanical exfoliated method,chemical exfoliated,chemical vapor deposition and physical vapor deposition.At the same time,the instrument methods and principles used in our experiments are also introduced,including optical microscope,fluorescence and Raman spectroscopy,X-ray photoelectron spectroscopy,atomic force microscopy,and scanning electron microscopy.In the third chapter of this thesis,we use chemical vapor deposition(CVD)technology to synthesize monolayer in one step using metal molybdenum as the source.In this chapter,we also discuss the influence of the amount of reaction source,reaction time,reaction temperature and protective gas nitrogen(N2)flux on the synthesis of single-layer molybdenum disulfide,and explain the synthesis mechanism and characteristics of metal molybdenum as the source.Finally,the fluorescence and Raman spectroscopy of the prepared monolayer molybdenum disulfide were studied in detail,especially the effect of laser power density on the fluorescence spectrum.In the fourth chapter of this thesis,we propose a new "seed" method to prepare the single-layer molybdenum disulfide.The monolayer molybdenum disulfide synthesis is promoted by using tungsten trioxide as a seed.Through comparative experiments,we found that a certain amount of tungsten trioxide was added during the preparation process,so that the synthesis temperature range of the single-layer molybdenum disulfide is from 810 ? to 950?.The single crystal size of the single-layered molybdenum disulfide prepared is also found to be greatly improved up to 200 ?m.We believe that the addition of tungsten trioxide provides a stable nucleation center for the growth of monolayer molybdenum disulfide,which promotes the growth of molybdenum disulfide.