The Design And Electronic Properties Adjustment Of Two-dimensional Materials Based On Group ? Elements

Nanomaterials and devices designed based on the group VI elements are one of the important future development directions for spintronics.By using first-principles calculations,focus on two-dimensional(2D)material design,and consider the electronic properties and regulation of materials as the main research directions.We are committed to discovering and designing Dirac materials with massless and dissipationless,and semiconductor materials with excellent properties.Here,by using first-principles calculations,we propose for the first time a Se Te monolayer as a 2D candidate with these novel properties.We find that the square lattice exhibits anisotropic band dispersions near the Fermi level and a Rashba effect related to large SOC and inversion asymmetry,which leads to a Dirac semimetal state.Another prominent feature is that Se Te can achieve a topological state under a tensile strain of only 1%,characterized by the Z2 invariant and helical edge states.Our findings demonstrate that Se Te is a promising material for novel electronic and spintronics applications.Next,we report two different configurations of B2 Se monolayers with anisotropic Dirac cones.Fully optimized B2 Se,as a rare 2D pure planar pristine honeycomb structure,can maintain good structural integrity at higher temperatures up to 1000 K in ab initio molecular dynamics simulation,Young's modulus and Poisson's ratio show high anisotropy,the Fermi velocity of 106m/s is the same order of magnitude as graphene.Moreover,we analyze the rationality of the existence of Dirac cones in the structure through wave functions and symmetry.This work provides novel candidates for finding direction-dependent,massless,and dissipationless quantum devices.Inspired by recent experimental progress in the successful synthesis of honeycomb borene structures on Al(111)substrates,we designed a new 2D honeycomb B2 Se structure with a pure planar configuration by adding selenium atoms to the bridge site.The covalent bond between the selenium atom and the boron atom makes the structure more stable.We systematically studied its structure and properties.The ab initio molecular dynamics(AIMD)simulations showed that the structure did not undergo structural collapse and atom reconstruction at the temperature of liquid nitrogen.The 2D elastic constant satisfies the Born-Huang criteria and exhibits a high degree of anisotropy.Another prominent feature is that the B2 Se film has a node line formed by the crossing between an electron-like band and a hole-like band near the Fermi surface,and the node line is protected by mirror symmetry.Moreover,applying biaxial strain to the material will not break the mirror symmetry and cause damage to the node line.This work not only provides new research ideas for expanding new anisotropic electron transport quantum devices,but also provides theoretical ideas for the study of nodal line materials related to structural symmetry.Motivated by the recent experimental success and theoretical research of ?-Ge Se,to expand and discover more semiconductors with excellent properties,we performed first-principles calculations on the structure,electronic and optical properties of ?-Sn S.The monolayer ?-Sn S is an indirect band gap semiconductor with a band gap of 1.87 e V.The energy band near the Fermi level is mainly dominated by the p orbitals of S and Sn atoms.The ?-Sn S can be transformed from one stable phase B to another stable phase B' by lattice distortion.The material has spontaneous polarization with polarization intensity of 1.1 × 10-10 C/m,and a suitable energy barrier(5.437 me V)enables the ferroelectricity of the material to be applied.By applying biaxial strain,the band gap control of monolayer ?-Sn S and the regulation of anisotropic electron transport can be achieved.Another interesting feature is that monolayer ?-Sn S exhibits anisotropic light absorption properties in the visible and ultraviolet ranges.This work provides high-quality candidates for researchers to explore semiconductor materials with more tunable properties,and has broad application prospects in the fields of future optoelectronic devices and ferroelectric devices.