First-principles Study On The Design And Electronic Properties Of Two-dimensional Transition Metal Materials

The application of two-dimensional(2D)transition metal(TM)nanomaterials in various fields of new high-performance electronic devices has attracted extensive attention.Based on first-principles calculations,focus on 2D TM material design,and consider the geometric structures and electronic properties of three kinds of 2D TM materials.We commit to discovering and designing 2D TM materials with excellent properties and providing theoretical support and design ideas for the application of spintronic devices.Here,by using first-principles calculations,we propose square Pb FCl KMX(M=Cu,Au;X=S,Se)monolayers and bilayers as 2D TM candidates.We find that the structures exhibit direct semiconductor characteristics.Compared with indirect band gap semiconductor,direct band gap semiconductor is easier for electrons to transition and has higher carrier mobility.According to the analysis of the energy band structure,it is found that the band gap of the KMX monolayers are less than 1.0 e V,the bilayers are 1.2?1.4 e V.And the optical properties show KMX monolayers and bilayers have several dielectric peaks and absorption peaks,respectively.By calculating the carrier mobility,we find the KMX monolayers are over 10³cm² V^-1 s^-1,the electron mobilities of KMX bilayers can reach 10⁴ cm² V^-1 s^-1.Our findings illustrate that the higher electron mobility and effective light absorption make these films have broad application prospects as optoelectronic devices in optoelectronic field.Next,we study 2D TM Sc X(X=P,As)monolayers with corrugated shapes.We analyze the structural characteristics,energy band structure,the nodal-line is formed by band crossing and observe the contribution of atomic orbitals to energy band components near the Fermi surface.The molecular dynamics simulations verify that Sc X can maintain good structural stability at higher temperatures up to 1000 K.Young's modulus and Poisson's ratio show the anisotropy of the structure.The Fermi velocity exceeds 10⁵ m/s,which is the same order of magnitude as graphene.And we consider the optical and transport properties of Sc X.In addition,we analyzed the rationality of the nodal-line by wave functions and structural symmetry.This work not only provides new ideas for the expansion of new anisotropic electron transport quantum devices,but also provides candidates for researchers to explore more 2D TM nodal-line materials.Motivated by recent experimental research progress of 2D TM ferromagnetic material Cr₂Ge₂Te₆,we discover 2D TM hexagonal M₂Ge₂X₆(M=V,Cr,Mn;X=S,Se,Po)monolayers.The monolayers have good dynamic stability at room temperature of 300 K.Young's modulus and Poisson's ratio are calculated to observe the elastic properties to explore their mechanical stabilities.The eigenstates of the 2D TM ferromagnetic semi-metallic state of Mn₂Ge₂Se₆ and Cr₂Ge₂Po₆ monolayers have good Curie temperatures which are close to room temperature.The Cr₂Ge₂S₆ and V₂Ge₂Se₆ monolayers are direct band gap semiconductors with band gaps of 1.22 e V and 1.25 e V.And they can increase the Curie temperature and change the easy magnetic axis through biaxial strain regulation.Moreover,the Cr₂Ge₂S₆ and V₂Ge₂Se₆ monolayers exhibit anisotropic light absorption properties in the visible and ultraviolet regions.This work can provide researchers with more candidates and ideas for exploring ferromagnetic 2D TM materials with tunable Curie temperature,and it may obtain certain application value in the fields of optoelectronic devices in the future.