Investigation On Chemical Vapor Transport Growth Of Two-Dimensional Molybdenum Disulfide Films

The molybdenum disulfide(MoS2)changed from indirect band gap to direct band gap with the thickness decreased to monolayer,which has widely applications in electronic,optoelectronic devices.In this work,the controllable preparation is difficult,although there have been many reports on the preparation of MoS2 monolayer.In this paper,the Chemical Vapor Transport(CVT)deposition method with MoS2 solid powder as molybdenum source and water vapor(H2O)as transport agent is proposed to grow MoS2 monolayer.We found that the growth of MoS2 is promoted by H2O.In this work,the effects of carrier gas flow,H2O,growth temperature,growth time,pressure have been used to study the growth of MoS2 monolayer.We found that the nucleation density of MoS2 is increased by increasing gas flow and H2O.With the extension of growth time,the nucleation density increases,the crystal size increases,but the corrosion of the base for a long time(>120 min)is not conducive to the growth of the molecular layer.The growth of the low temperature(<900?)have adverse effect on nucleation and crystal growth,the growth of high temperature(900?1000 ?)is conducive to the formation of crystal nucleus,but the higher temperature is not conducive to the growth of the crystal.Low pressure is beneficial to the growth of large area monolayer.On the basis of mastering the law of the influence of experimental conditions on the growth of MoS2 monolayer,this paper discusses the growth mechanism of MoS2 monolayer by CVT method.In the last part of this paper,we study the effects of other chemical gas transport agents and crystal nucleation promoters on the growth of MoS2 monolayer.The results show that the growth of MoS2 monomolecular layer has been hardly affected by iodine(I2),which commonly used in CVT.The growth of MoS2 monomolecular layer can be promoted by NaCl,but its quality is not high.A further study needs to be made.