Controllable Synthesis Of Wafer-scale Two-dimensional Materials

Material is the product of the progress of human civilization,and it is also a powerful force for the progress of human civilization.High-performance materials have been the focus of human research for a long time.The discovery of semiconductor materials and related devices has brought mankind into the information age,and the development of nanoscience and technology has enabled mankind to explore the novel properties of atoms and molecules on the nanoscale,and to manufacture widely used multifunctional nanoelectronic devices and circuits.Two-dimensional(2D)materials are a unique class of nanomaterials,whose longitudinal dimensions are generally less than 100 nm and horizontal dimensions can reach several meters.Due to 2D materials unique structure,it has shown exciting potential applications in the fields of electronics,optoelectronics,valley electronics,spintronics,etc.At the same time,some new interesting characteristics have been discovered,such as losslessness in 2D topological insulators,scattered edge states,2D ferroelectricity,and magnetism.So far,a large number of 2D materials have been successfully prepared,such as transition metal disulfides(TMDs)(such as WSe₂,WS₂,MoSe₂,MoS₂),metal halides(such as CdI₂,BiI₃),and MXene materials(such as Ti C,Mo C)Wait.At present,researchers have proposed many preparation methods,such as mechanical lift-off,liquid-phase lift-off,hydrothermal synthesis,molecular beam epitaxy(MBE),magnetron sputtering,pulsed laser deposition,atomic layer deposition,chemical vapor deposition(CVD),etc.Because the 2D materials prepared by CVD have the characteristics of high quality,controllable number of layers,high yield and low cost,they are considered to be one of the most important preparation methods for 2D materials.In the process of CVD growth of 2D materials,the number of nucleation points,the size and quality of the epitaxial material are closely related to the choice of substrate.How to choose a suitable substrate to achieve controllable nucleation and high-quality epitaxial growth is a major challenge for 2D material growth.On the other hand,large-area ultra-thin 2D materials are the basis for the development of next-generation electronic and optoelectronic devices and large-scale integrated circuits.In the field of semiconductors(or chips)in the future,the synthesis of large-area ultra-thin 2D materials will become the most critical step,which will determine whether 2D materials can be industrialized and can be truly applied to all aspects of people's daily lives.However,the current large-area ultra-thin 2D material is also a very significant challenge.Based on this,this thesis used CVD and MOCVD systems to successfully achieve the controlled growth of high-quality single crystals and wafer-scale TMDs on different substrates.The research results obtained in this thesis are summarized as follows:1)This thesis first reviewed and summarized the physical and chemical properties of various substrates and their important roles in the synthesis of 2D materials in the form of a review.Then,using the CVD method,the growth of high-quality single crystal WSe₂nanosheets was successfully realized on Si O₂/Si,sapphire,mica flakes and molten glass substrates,and the influence of the substrate on the growth of WSe₂was explored.This work provides a theoretical and experimental basis for the choice of substrate in 2D material synthesis.2)In this thesis,we used a customized vertical cold-wall MOCVD system to grow 2D TMDs,and successfully synthesized wafer-scale,high-quality and ultra-thin2D MoS₂films on SiO₂/Si substrates and sapphire substrates.This work lays the foundation for the realization of practical applications such as electronics,optical devices,and large-scale integrated circuits.3)In this thesis,2D BiOCl nanosheets with large size and ultra-thin were synthesized by CVD system.This work provides a high quality base material for photoelectric applications and other studies of BiOCl materials.