Preparation Of Monolayer MoS₂/WS₂ With NaCl And Grain Boundaries And Electrical Properties Study

The excellent performance of graphene,a typical two-dimensional material,has inspired researchers to study two-dimensional materials.Two-dimensional transition metal chalcogenide disulfide materials are prepared in various ways,including mechanical lift-off,electrochemical lift-off,liquid-phase ultrasonic lift-off,hydrothermal（solvothermal）,and chemical vapor deposition（CVD）.Among them,the chemical vapor deposition method can achieve controlled growth of the size and number of layers of the material by adjusting a series of growth parameters.It can prepare a high-quality,large-area single-layered two-dimensional material,which is highly expected to be industrialized.In addition,the chemical vapor deposition method can also achieve specific doping or modification of the material through external introduction.In this paper,a single-layer MoS₂ and WS₂ material was successfully prepared by sodium chloride-assisted chemical vapor deposition.The influencing factors of its growth（growth temperature,growth time,type and proportion of halides,flow rate of carrier gas,etc.）were studied in series,and the optimal growth conditions of two-dimensional MoS₂ and WS₂ under this experimental system were determined.The detailed analysis of the prepared monolayer MoS₂ and WS₂ was carried out by optical microscopy,transmission electron microscopy,Raman spectroscopy and atomic force microscopy.There are some deficiencies in the preparation of two-dimensional TMDs by chemical vapor deposition.After research,it has been found that there are some inherent defects in crystal structures of two-dimensional TMDs,such as atomic dislocations,vacancies,impurity substitutions,and grain boundaries.Although these defects affect the intrinsic properties of the materials,they are some opportunities for the study of defect engineering.It is necessary to solve the problem of defect observation,which is especially the grain boundary observation of two-dimensional materials,in order to development of the defect engineering research.The previous grain boundary research methods have many limitations,such as complicated operation,time-consuming,introduction of artificial defects,etc.This article has developed a simple and efficient method to observe the grain boundary of two-dimensional material by optical microscopy.It is deposited gold or copper on the target sample with annealing treatment.The method is simple and reliable.It has a wide observation range and does not need to transfer the two-dimensional material.It also avoids artificially induced defects.At the same time,this experiment was not only confirmed by SEM,AFM,etc.but carried out research on the universality of the method,and confirmed that has good applicability to other 2D-TMDs materials.In addition,this experiment also uses the monolayer MoS₂ and WS₂ to build a field effect transistor for electrical performance testing.Found that the material obtained has very good electrical properties.