First-Principles Study Of The Domain Boundary Defects In Two-Dimensional MoTe₂

In the wake of the first mechanical exfoliation of graphene in 2004,atomically thin two-dimensional?2D?layered materials have attracted an upsurge of interest during the past decade.As a result,one kind of vital 2D materials 2D transition metal dichalcogenides?TMDs?is coming into play on account of their numerous fascinating properties.Typical TMDs include MoS₂,MoSe₂,and MoTe₂ etc..Bulk MoTe₂ is an indirect band gap semiconductor,but when the thickness decreases to monolayer,it exhibits a direct band gap of 1.10 eV as a consequence of the quantum confinement effect.In 2011,MoTe₂ single layers have been firstly obtained through liquid exfoliating in the experiments.This monolayer material exhibits a charge carrier mobility greater than that of MoS₂,extends the spectral range of atomically thin direct-gap materials from the visible to the near-infrared.Whereafter,structural defects are ubiquitous when large-scale single layer materials were synthesized under fluctuating growth conditions by using the CVD or CVT method.Previous experimental studies have shown that a number of different defects exist in the monolayer TMDs,covering point defects and boundaries.The defects could significantly influence the geometric,mechanical,optical,thermal,and electrical properties of the material.Furthermore,intrinsic structural defects in 2D TMDs provide an exciting opportunity to modulate the local properties on new application.In recent years,the electronic properties of the defects of MoS₂,MoSe₂,WS₂,etc.have been intensively studied in both experimental and theoretical research.Motivated by the questions above,in this article,we have systematically studied the electronic and magnetic properties of intrinsic defects including point defects,boundaries,and superstructure in monolayer MoTe₂ by means of DFT simulations.The main work and innovation points in this study are summarized as follows:1.The magnetism of intrinsic point defects in MoTe₂ monolayer.For the point defects,all the vacancy defects including V_Te,V_Te2,V_MoTe3,V_MoTe6 do not induce magnetism in MoTe₂ monolayer.However,the antisite defect Mo_Te2 induce a biggish spin polarization,leading to the formation of local magnetic moments of 1.93?_B in the single layer MoTe₂.The main contribution to the spin polarization results from the nearest Mo atoms,and the other atoms in the supercell almost do not have any contribution to it.The magnetic moment is mainly contributed by the p orbital of the Te atoms and the d orbital of Mo atoms with an asymmetric spin-up and spin-down DOS near the Fermi level.2.The magnetism of boundary defects in MoTe₂ monolayer.For the boundary defects,with the exception of 4l4a,other types of boundaries including 5|7a,5|7b,4|8,4|4b,6|6a,6|6b,8|8a and 8|8b induce spin polarization and lead to the formation of local moments,which is come from the 4d orbital of Mo atom around the boundary.Compared with the nonmagnetic pristine MoTe₂ monolayer,the introduction of magnetic defects makes it having wider and better applications for spintronics devices.For the magnetic boundary defects,the principle of the magnetic moment magnitude for Mo atoms in different positions can be summarized as that the coordination number of Mo atom and its distance from the boundary center have a major impact on it.With the same coordination number,the smaller distance of Mo atom to boundary,the larger magnetic moment of Mo atom.When the coordination number is different,the Mo atom has the larger magnetic moment with the more coordination number.It is worth noting that 6|6a shows a spin gapless band structures,which could have wide applications for creation and manipulation of spin-polarized carriers in spintronics.The 4|4b and 8|8b boundary shows a metallic band structure,which can serve as a perfect one-dimensional metallic wires embedded in the other semiconducting MoTe₂ and could provide more functionalities by forming intrinsic electronic heterostructures in single layer MoTe₂.Our results could shed light on the design of novel nano-and magnetic electronics based on MoTe₂ by structure modulation.3.The magnetism of superstructure in MoTe₂ monolayer.we firstly study the stability of the superstructure in MoTe₂ monolayer.Taking into account the number of extranuclear electrons in Mo atom,the electronic structure of monolayer MoTe₂ was studied with the PBE effects as well as PBE+SOC methods,and a appropriate electronic band structure was obtain by PBE approach.All types of superstructure induce spin polarization and lead to the formation of local moments,which is come from the vertices Mo atom around the boundary.The charge of superstructures have a redistribution at the boundary.More charge transfer around the boundary suggests a strong ionic bond,leading to the charge accumulation near the interface.