First-principles Study On Doping Modification Of Single-layer WS₂

Spintronic devices made of half-metal(Half-metal,HM)ferromagnetic materials play an important role in modern information technology.Therefore,it is necessary to theoretically and experimentally try various methods to introduce ferromagnetism into nonmagnetic transition-metal dichalcogenides(Transition Metal Dichalcogenides,TMDCs)and effectively control the electron and magnetic properties of TMDCs to expand its application.Like other materials,defects are inevitably produced during the preparation of monolayer tungsten disulfide(WS2),which greatly affects the electrical,magnetic and optical properties of the material.However,sometimes the existence of defects is not a bad thing,because they can control the properties of materials in a controlled manner.For example,extensive experimental and theoretical studies have effectively altered the magnetic properties of WS2 by forming vacancies,alternatively doping transition-metal(Transition Metal,TM)atoms,adsorbing nonmetal atoms,applying an external electric field,or elastic strain.Inspired by this,our paper systematically studied the structural and magnetic properties of monolayer WS2 after doping a single nonmetal atom,a single TM atom,and Fe-nonmetal cluster based on first-principles method.First,we systematically studied the case of alternative doping of a single nonmetal atom X(X=N?P?As?Sb?Cl?Br?I or At)at the S position.The results show that regardless of the p-type or n-type doped monolayer WS2 system,the greater the atomic radius of the dopant X.the larger the bond length(dx-w)and height difference(hs),but the smaller the bond angle(?w-x-w).Furthermore,by comparing the formation energies(Efom)of the doping system,we have found that all doped systems are easier to form and more stable under Wnich conditions than under Snich conditions.Interestingly,although the pristine monolayer WS2 system is a nonmagnetic semiconductor,the I and At doped systems are converted to magnetic HM.The above results indicate that nonmetal substitution for S atom is a useful method of modulating the electron and magnetic properties of a monolayer WS2 system.Then,we systematically studied the alternative doping of a single TM atom X(X=Fe?Ru or Os)at the W position.The results show that the W-S bond exhibits strong covalentity,but it is clearly weakened after the W atom is replaced by a single X atom.In addition,the smaller total energy reveals that the spin-polarized doping system is more energetically favorable to the non-spin polarized state,and the case of Os doping in spin-polarized state is the most stable of the three doping systems.Furthermore,although the pristine monolayer WS2 system is a nonmagnetic semiconductor,a single TM atom Fe and Ru doped monolayer WS2 system are transformed into a magnetic HM.The above results indicate that it is a feasible method to modulate the electron and magnetic properties of the monolayer WS2 system by replacing the parent W atom with a transition metal atom X.Finally,based on the above two doping methods,we have systematically studied the case where a transition metal atom Fe and six nonmetal atoms X(X=S?N?O or F)jointly replace one W atom in the matrix and its nearest six S atoms.The results show that although the total magnetic moment of the isolated Fe atom is 4?B,but in the monolayer WS2 system doped with Fe-S6,Fe-N6,Fe-O6 and Fe-F6,the magnetic moment of the dopant Fe are 1.193 ?B,1.095 ?B,-3.019?B and-3.269 ?B,respectively,which means that there is a strong hybridization between the dopants Fe and S/N,but there is a weaker hybridization with O/F.Although the pristine monolayer WS2 system is a nonmagnetic semiconductor,the clusters Fe-S6 and Fe-F6 doped monolayer WS2 systems become magnetic HM.In addition,the absorption edges of the clusters Fe-N6,Fe-O6 and Fe-F6 doped monolayer WS2 systems show a red shift relative to the pristine monolayer WS2 system,which significantly increases the absorption of visible light and can therefore be used as Potential solar absorbers.Compared to monoatomic doping,cluster doping seems to have more advantages because its constituents can be selectively selected,the physical properties it exhibits may exceed a single constituent atom,and clustering can be avoided due to its high stability.