Performance Tuning Of One-dimensional Janus MoSSe Nanomaterials Based On First-principles Method

Transition metal dichalcogenides(TMD)has been widely studied because of the natural band gap and remarkable physical properties.The Janus Mo SSe(JMo SSe)nanomaterials studied in this thesis are a new type of TMD,and its monolayer structure has been successfully synthesized by experiments.Due to the structural symmetry breaking,JMo SSe nanomaterials has extraordinary properties,such as intrinsic vertical piezoelectric effect,enhanced Rashba spin-orbit interaction and optically active vertical dipole,which make the new material have a good promising application in lithium-ion batteries,optoelectronic devices,catalysts,spin electronic devices and so on.One-dimensional TMD is considered to be a very promising candidate material in the new generation of nano-devices because of its unique morphological characteristics and significant physical properties.The rich edge characteristics make one-dimensional TMD nanomaterials more sensitive to the effects of edge modification and strain.Thus,the researches on the tuning of one-dimensional TMD nanomaterials will help to improve the flexibility of one-dimensional TMD nanomaterials in device design and application.Therefore,first-principles calculation method based on density functional theory(DFT)is applied to the researches of JMo SSe nanoribbons(JMo SSe NR)and JMo SSe nanotubes(JMo SSe NT)in this thesis.The micromechanism of physical properties of one-dimensional JMo SSe nanomaterials under different tuning methods is studied systematically,which provides theoretical guidance for the future device application based on one-dimensional JMo SSe nanomaterials.The main research contents and results are listed as follows:(1)The effects of edge modification on the structural stability,electronic structure and magnetic properties of Zigzag JMo SSe NR(ZJMo SSe NR)are studied.The results show that ZJMo SSe NR is a magnetic metal material,and different types of edge modification can improve the stability of ZJMo SSe NR from varying degrees.Among them,the structure of ZJMo SSe NR is the most stable when H atom and O atom are adsorbed on the edge,and it is interesting that the magnetic moment decreases with the increase of the width of the nanoribbon.In addition,different types of edge modification make the spin density of ZJMo SSe NR edge redistribute and the magnetic moment is reduced.(2)The effects of edge modification on the structural stability,electronic structure and magnetic properties of Armchair JMo SSe NR(AJMo SSe NR)are studied.The results show that the bare AJMo SSe NR is an indirect band gap semiconductor with a band gap of 0.46 e V.Different types of edge modification can effectively improve the stability of AJMo SSe NR and tune the band structure.Among them,the structure of AJMo SSe NR is the most stable when H atom and O atom are adsorbed on the edge,and the band gap is significantly increased(from 0.46 e V to 1.36 e V).AJMo SSe NR becomes direct band gap semiconductor when H atoms are absorbed on the edge.When the edge modification is H/N,H/P or H/F,AJMo SSe NR show magnetic properties.(3)The effects of tube diameter and strain on the electronic structure and optical properties of Zigzag JMo SSe NT(ZJMo SSe NT)are studied,and the internal mechanism of the change of the electronic structure and optical properties is further analyzed.The results show that ZJMo SSe NT is a direct band gap semiconductor.The band structure and optical properties can be effectively tuned by the diameter.With the increase of the compression strain,the peak position of dielectric constant of ZJMo SSe NT is red shifted.With the increase of the tensile strain,the dielectric constant of ZJMo SSe NT does not change obviously,but the phenomenon of competitive switching at the bottom of the conduction band occurs.(4)The effects of tube diameter and axial strain on the electronic structure and optical properties of Armchair JMo SSe NT(AJMo SSe NT)are studied,and the internal mechanism of the change of electronic structure and optical properties is further analyzed.The results show that AJMo SSe NT is an indirect band gap semiconductor material,and its band structure and optical properties can be effectively modified by the diameter of the tube.After applying the strain,the band gap of AJMo SSe NT decreases with the increasing strain,and the dielectric constant is generally sensitive to the compressive strain while insensitive to the tensile strain.