First-principles Study Of Transition Metal Atom Doped Monolayer WS₂

In this paper,the structures,electronic and magnetic properties of a single and double identical TM atoms Mn,Fe,Co and Ni doped WS₂ systems are investigated using the first-principles methods based on the DFT.We find that a single TM atom doped monolayer WS₂ systems exhibit the magnetic HM characters with the total magnetic moments Mtot of 1,2,3 and 4?B and the smaller spin-down gaps Eg of 1.262,1.154,1.407 and 1.073 eV for Mn,Fe,Co and Ni,respectively.Comparing with the formation energy Eform,we find that it is relatively easier to incorporate Mn,Fe,Co or Ni atom into WS₂ nanosheet under S-rich experimental conditions.Moreover,the Eform increases for Mn,Fe,Co and Ni doped cases successively,indicating the Mn doped WS₂ nanosheet system is the most stable.For the double identical TM atoms Mn,Fe,Co and Ni doped WS₂ systems at the first?0,1?,second?0,2?and third?0,3?nearest-neighbor cation site configurations,except for the cases of two Ni atoms doped at the first?0,1?,second?0,2?and third?0,3?nearest-neighbor cation configuration which are AFM,FM and FM metals,respectively,the other cases are all HM ferromagnets.The total magnetic moment Mtot increases not only for double identical TM dopants Mn,Fe,Co and Ni?except for?0,1?AFM case?successively at the same nearest-neighbor cation configuration but also for each of the double identical TM dopants at the first?0,1?,second?0,2?and third?0,3?nearest-neighbor cation configurations successively.Next,the structure,electronic,magnetic and optical properties of Mn-X?X=B,C,N,O,F,Cl,Br,I,At?co-doped monolayer WS₂ systems are theoretically studied.We find that the Mn-B,Mn-N,Mn-F,Mn-Cl,Mn-I and Mn-At co-doped monolayer WS₂ systems remain the nonmagnetic semiconducting character with the smaller band gaps of 1.094,0.839,0.667,0.578,0.558 and 0.564 eV respectively.While the Mn-C and Mn-O co-doped monolayer WS₂ systems exhibit the magnetic semiconducting characters with a total magnetic moment Mtot of 1 ?B,the spin-up gaps?spin-down gaps?of 0.541?1.168?and 0.608?1.436?eV,respectively.The Mn doped and Mn-Br co-doped monolayer WS₂ systems change to HM ferromagnet with a total magnetic moment Mtot of 1 ?B and-2 ?B,the spin-down band gap of 1.262 eV?spin-up band gap of 1.321 eV?and thus useable in the spintronic devices.The positive binding energies E,show all the Mn-X co-doped monolayer WS₂ systems will not easy decompose once they have been formed,especially for the Mn-F co-doped monolayer WS₂ system with the highest binding energy Eb.Furthermore,the Mn doped monolayer WS₂ system has the highest static dielectric constants ?1?0?and ?2?0?,refractive indices n?0?and k?0?among the doped systems.Meanwhile,for all studied systems from 2.5 to 7.5 eV,the r???and k???present an oscillation behavior.The absorption coefficients ????show the pure monolayer WS₂ system has the highest transmittance in low energy region.Meanwhile,the pure monolayer WS₂ system has larger absorption from 6 to 9.5 eV and thus is more suitable to make a near-ultraviolet?6-9.5 eV?photodetector,while all doped monolayer WS₂ systems are more suitable to make an infrared photodetector due to their red-shift phenomenon.