A First Principle Study On The Modification Of MoS₂ Properties By Atoms And Molecules

Because of the reduced dimensions,two-dimensional?2D?matrials possess many exellent properties that do not have been found in bulk matrials.The first piece of 2D material is graphene,prepared from graphite by mechanical peeling about ten years ago.Now,a large family of 2D materials was come into being,for the great efforts and enthusiasm devoted by the worldwide researchers.Among them,monolayer molybdenum disulfide?MoS₂?is one of the most outstanding matrials and a large amount of attention has been paid to it.MoS₂ is direct-gap semiconductor,and can be used in many field,such as field effet tube?FET?,optoelectronic devices and chemical catalysis and so on.In order to make a better application of MoS₂,the modifcation of properties of MoS₂ is nessesary.In this thesis,first principle calucations were adopted to study the halogenation of MoS₂,adsoption behaviors of gas molecules at defective MoS₂ and the magnetic atomic chains on MoS₂.1.The halogenation of MoS₂.Halogen?F,Cl,Br and I?monomers can adsorb on MoS₂ stably.All these systems are magnetic with 1 ?B moment due to the asymmetry impurity states induced by adatoms.Once another adatom was adsorbed,long-range antierromagnetic?AFM?develop.We further fully halogenate one side of MoS₂.F-MoS₂ can stabilize in bonding state with large binding energy and a titled configuration.Upon semiflurination,MoS₂ transferred from semicoductor to metal.Cl-and Br-MoS₂ can be in bonding or nonbonding state,however,the energy of nonbonding state lower than bonding state in the two sytems.I-MoS₂ can only be in nonbonding state.2.The adsorption of gas molecules,CO₂,N₂,H₂O,CO,NH3,NO,O₂,H₂ and NO₂,on MoS₂ with sulfur vacancy?SV?.CO₂,N₂ and H₂O physisorb at the vicinity of SV,however,SV will strengthen the adsorption.CO,NO,O₂ and NH3 chemisorb at SV,forming new bonds,Mo-C,Mo-N and Mo-O.The Mo-O bond will eliminate the defective states induced by SV.The H₂ and NO₂ molecules were found to dissociate at S vacancy.The dissociation of NO₂ molecules resulted in O atoms located at the S vacancy site and NO molecules physisorbed on O-doped MoS₂.3.The magnetic properties and adjustment of magnetic atomic chains?V,Cr,Mn and Fe?on the sulfur vacancy line?SVL?of MoS₂.All magnetic chain can adsorb at SVL stably,and their magntic properties influenced by MoS₂ dramatically.Upon the anchoring on MoS₂,the magnetic order of V and Cr chains remain unchanged,but the weaken the magnetic interactions.However,transitions from ferromagnetic to antiferromagnetic were happened to Mn and Fe induced by MoS₂ substrate.The electronic magnetic properties of atomic 3d transition-metal chain on SVL of MoS₂ can be tuned by the uniaxial strain that applied along chain direction.Compressive strain transfers V/MoS₂ from ferromagnetic metal to antiferromagnetic metal.Transition from antiferromagnetic narrow gap semiconductor to ferromagnetic metal will occurs to Cr/MoS₂ and Mn/MoS₂ by-2.5%compressive strain and 5%tensile strain respectively.Fe/MoS₂ can transfer from antiferromagnetic semiconductor to metal by-5%compressive strain.