Preparation Of Few-layer Molybdenum Disulfide Thin Films By CVD Method And Its Gas Sensing Propertises

Because of its excellent physical,chemical and mechanical properties,graphene has attracted extensive attentions from domestic and foreign scholars.MoS₂ possesses a graphene-like structure and has a high specific surface area,which increases the contact area with gas molecules and makes it have an application potential in the field of gas sensors.However,the MoS₂ structures used in the gas sensors are mostly prepared by a mechanical or chemical exfoliation method.The obtained MoS₂ films have small sizes and uncertain layer numbers,and the reproducibility is poor,which is not conducive to the large-scale production of gas sensors based on Mo S₂.What.'s more,there appeared a saturation phenomenon in the gas sensing of MoS₂,and the response and recovery time of MoS₂ gas sensor reach up to tens of minutes.In this paper,continuous MoS₂ thin films with large areas were prepared by chemical vapor deposition?CVD?method,and their gas sensing performance was studied.The main contents are as follows:1.The effects of pressure,the mass of S,gas flow rate,growth time and growth temperature on the experimental results were investigated.optical microscope,X ray diffraction?XRD?,X ray photoelectron spectroscopy?XPS?,Raman spectroscopy?Raman spectra?,atomic force microscopy?AFM?and transmission electron microscopy?TEM?were used to characterize the samples.The results show that the pressure mainly affects the morphology of MoS₂,the mass of S directly controls the degree of MoO3 vulcanization,the gas flow rate indirectly affects the degree of MoO3 vulcanization by controlling the amount of S into the reaction atmosphere,the growth temperature mainly affects the critical of MoS₂ nucleus to control the nucleation point and the size of MoS₂,the growth time mainly affects the size of MoS₂.When the pressure is atmospheric pressure,the mass of S is greater than 1g,the gas flow is 30 sccm,the growth temperature is 750? and the growth time is 20 min we successfully prepared MoS₂ thin film with an area of ⁴mm×5mm.In addition,a thin layer of MoS₂ thin film with an area of ¹0mm×15mm was prepared by two-step method on the basis of the best experimental conditions of one-step method.2.The gas-sensing performance of the prepared MoS₂ thin film was tested by gassensing analysis system.The results show that MoS₂ had the best selectivity to NO2 gas at room temperature and the detection limit of NO2 gas was as low as 1ppm,with the sensitivity up to 2.6%.The response and recovery time for 20 ppm NO2 were 320 s and 900 s,respectively.3.In order to further improve the gas-sensing properties of MoS₂,precious metal Pt was sprayed on the surface of MoS₂ film to improve the structure.The sensitivity of the MoS₂ thin film modified by Pt to NO2 was improved,and the sensitivity increased from 2.6% to 3.46% at the detection limit of 1ppm.Moreover,the response time to 20 ppm NO2 was 210 s,shortened by 110 s.