Tunable Electronic Structure And Magnetic Properties Of Two-dimensional Cr₂C And CrC₂ Monolayers

Owing to the successful exfoliation of graphene,the two-dimensional(2D)materials become one of the hot topics in the field of condensed matter physics and materials science.Carbon-based materials have a variety of bonding modes,which exhibit rich structures and physical properties.In this dissertation,the electronic structure and magnetic properties of Cr₂C and CrC₂ monolayers were investigated by first-principles calculations,which provide the theoretical basis for the low-dimensional electronic devices.The valley polarization of 2H-VS₂ monolayer is well preserved in two-dimensional 2H-VS₂/Cr₂C heterostructures.In a certain stacking pattern,the valence band maximum of 2H-VS₂ turns from?to K'.The magnetization direction can tailor the spin and valley polarization.When V(S)atoms locate right above Cr(C)atoms,2H-VS₂ monolayers show the in-plane magnetic anisotropy(IMA).In other models,2H-VS₂ monolayers exhibit the perpendicular magnetic anisotropy.Valley polarization in 2H-VS₂/Cr₂C heterostructure can be modulated by biaxial strains.The valley of 2H-VS₂ monolayers at K'point has the spin polarization of 100%in a large energy range.The IMA of 2H-VS₂ monolayers increases as the tensile strain increases.As the interlayer distance decreases,the interlayer interaction between 2H-VS₂ and Cr₂C monolayers increases.Surface functionalization can affect the electronic structure of 2D materials.Monolayer CrC₂ shows different band structures when different functionalized atoms are adoped.By being functionalized with O atoms at high symmetry point X on both sides(named 2O_X),the monolayer CrC₂ shows the bipolar half-metallic characteristics.It is a bipolar magnetic semiconductor by H atoms functionalization(named 2H_X).The 2O_X model is fully spin-polarized in spin-up channel at Fermi level,which is robust against the uniaxial strain and electron(hole)doping.The fully spin-up(down)polarized carriers appear in 2H_X model by 0.1e hole(electron)doping per unit.These results present the theoretical basis for designing the 2D spintronics devices.