Synthesis Of Two-dimensional Heterojunction And Study On Their Sensitive Properties

With the rapid development of integrated circuits,the pursuit of integrated circuits with lower cost,smaller size and lower power consumption has become higher and higher.Two-dimensional materials will become one of the innovative materials in micro-nanoelectronic materials and optoelectronics due to the superior physical and chemical properties and adjustable bandgap.Molybdenum disulfide?MoS₂?has a typical two-dimensional layered structure with a indirect band gap of 1.2 eV.As the number of layers decreases,its band gap gradually increases.Monolayer MoS₂ shows a direct band gap of 1.8 eV,which can be a good material for the fabrication of optoelectronic devic4es.This work studied firstly the controllable preparation of MoS₂ by chemical vapor deposition method.Secondly,the preparation of two-dimensional heterostructure was studied.Finally,the preparation and sensing properties of field effect transistors based on MoS₂ were studied.The main results obtained are as follows:1.MoS₂ with different sizes were prepared by chemical vapor deposition.The size,formation,crystallinity and layered structure of MoS₂ were characterized by optical microscopy,fluorescence microscopy,scanning electron microscopy,atomic force microscopy,transmission electron microscopy and Raman spectroscopy.The triangular MoS₂ with a size of 1-120?m were observed in both the optical microscope and the fluorescence microscope.Scanning electron microscopy?SEM?also confirmed that the MoS₂ single crystal was triangular in shape.Atomic force microscopy found that the thinnest MoS₂ was around 0.7 nm,indicating a single layer structure.The EDS mapping analysis showed that the Mo and S elements were uniformly distributed in the MoS₂ triangle.Raman spectroscopy revealed two characteristic peaks of MoS₂,E¹_2g and A_1g.Our systematic studyies given the optimal parameters for MoS₂ growth:growth temperature 750-800°C,growth time 10-15 min,argon flow rate 20 sccm.In addition,the vertical Graphene-MoS₂ heterojunction was successfully fabricated by CVD process,paving the way for exploring more excellent performance.2.The fabrication of field effect transistor based on monolayer MoS₂ was realized by an optical lithography process.The FET device show good FET characteristics with switching current ratio up to 10⁵ and the mobility around 1.15cm ² V^-1 s^-1.3.A gas sensor was prepared by using MoS₂ as a gas sensitive material.The response-recovery characteristics of the devices towards ethanol,acetone,toluene,ammonia were studied.It was found that the gas sensor has a fast response to ethanol and acetone vapor.The response time of ethanol is 4s,and the response time of acetone is 2s.