A First-principle Study Of The Influence Of Doping On The Gas-sensing Performance Of A Single-layer MoS₂

Due to high gas sensitivity,good long-term stability and short response/recovery time,semiconductor gas sensor has become the most widely used and researched gas sensor.Moreover,it is playing an important role in human life.However,the traditional oxide semiconductor gas sensor has the disadvantages of high working temperature and poor repeatability,which deeply restrict its application.Monolayer MoS₂,as a typical 2D transition-metal dichalcogenides,has been widely applied in many fields.Because of quantum confinement effect,MoS₂ monolayer has unique mechanical,electrical,catalytic and optical properties.Compared to the traditional body semiconductor material,MoS₂ monolayer has a huge specific surface area,so it has a high application prospect in the field of gas detection.Recently,the problems of air pollution and industrial production safety are becoming more and more serious.Even trace toxic and harmful gases could lead to enormous damages.Therefore,the development of high-performance gas sensor is particularly important.Similar to graphene,MoS₂ monolayer can also be applied as gas sensing material.Because of outstanding physical and chemical properties,MoS₂monolayer acts as a new type of gas sensing material and plays an important role in environmental monitoring and industrial production.Based on first-principles method,the influence of doping treatment on the gas sensing properties of MoS₂ monolayer is studied in this paper.The main jobs of the work are as follows:?1?Supercell structure of Ag doping MoS₂ monolayer was constructed,and the energy and electronic structure were calculated.It is found that Ag atom is steadily embedded in the S vacancy on the MoS₂ monolayer.Moreover,the conductivity of the basement is improved because of the doping of Ag atom.Then,three gas molecules?NO,NO₂ and NH₃ molecules?were adsorbed on the surface of the doping basement.The calculation results show that the gas sensitivity of the MoS₂ monolayer is improved.The adsorption reactions between the basement and NO₂/NH₃ molecules are chemisorption.But the reaction between NO molecule and the basement is still physisorption.Owing to the opposite direction of electron transfer between two molecules?NO₂ and NH₃ molecules?and Ag-MoS₂ monolayer,the Ag doping basement exhibit gas selectivity among three gases.?2?The models of Ag-Si,P,Cl co-doping MoS₂ monolayer are constructed.The structure stability and electronic structure of the doping system are calculated,respectively.The results show three co-doping systems are stable.Additionally,along with the increasing of non-metal doping atom number,Fermi level gradually moves to conduction band and work functions gradually decrease.After adsorption of NH₃ on MoS₂ monolayer,energy calculation shows that three adsorption configurations all belonged to chemisorptions.Moreover,hybridization of p-d orbitals exists between NH₃ molecule and co-doping systems.Besides,the number of electron transfer between NH₃ molecule and doping system is decreasing.This interesting phenomenon could be explained via Schottky-contact-barrier model method.?3?In order to further expand the application of MoS₂ monolayer in the field of gas detection,the model of Al doping MoS₂ monolayer was built.Firstly,the energy and electronic structure of Al doping system are calculated.It is found that the Al dopant could exist steadily,and Al doping behaves as donor doping.After doping processing,the conductivity of the system is improved.Three gas molecules?CH₄,SO₂ and NH₃ molecules?were adsorbed on the basement.The energy and electronic structure are calculated,the results show that only NH₃ molecule adsorption reaction belong to typical chemisorption.The NH₃ molecule adsorption configuration is more stable than the Ag doping adsorption configuration.Furthermore,the number of electron transfer between NH₃ monolayer and Al-MoS₂ monolayer is more than that of Ag doping,which reaches to 0.38e.It reveals Al doping MoS₂ monolayer shows gas selectivity in three gases.