Electronic And Magneto-Electronic Properties Of Antimonene Nanotubes And Heterojunctions

Antimonene,a newly emerging group VA two-dimensional material,has been predicted to hold significant potential applications in the next generation of logic circuits,optoelectronic devices,catalysis and energy devices due to its unique electronic properties.However,due to its large band gap and intrinsic non-magnetic behaviors,its application in electronic and magnetic devices is limited greatly.In this thesis,we theoretically study how to modify properties of antimonene and its related structures,such as the magnetic introduction for its nanotubes and the construction of heterojunctions to improve the electronic and optical properties,by the first-principles calculation method based on density functional theory.The main contents are as follows:First,we make investigations on antimonene nanotubes,which are a class of important derivatives of Antimonene.To induce magnetism for them,low concentration transition metal TM(TM=Sc,Y,V,Nb,Fe,Ni,Co and Rh)atoms are considered theoretically to be adsorbed on antimonene armchair nanotubes(SbANTs).Highly geometrical stability of these TM-adsorbed nanotubes is identified by the calculated adsorption energy and molecular dynamics simulation,and the TM-Sb bond lengths are proven to be closely related to their relative electronegativity.Meanwhile,we also find that the intrinsic magnetic moment of TM atom plays a decisive role in inducing SbANTs magnetism,and the weakened or quenched TM atom intrinsic magnetism is intimately related to the valence electron configuration expansion and charge transfer.The strong interaction and coupling between the TM d-orbital and Sb p-orbital lead to variously favorable magnetic phases such as spin bipolar semiconductor and half-semiconductor,which is predicted to be stable beyond room temperature.The TM adsorption can also effectively regulate the tube carrier mobility to the difference of several orders of magnitude as well as result in the significant carrier polarity and spin polarity of mobility.Also shown is that very strong electric-magnetic coupling effects cause the continuous transition of magnetic phase,providing the possibility to realize magneto-electric materials.And the noticeable Stark effect is also observed.Subsequently,to improve the electronic and optical properties of antimonene,the Sb/WS2 heterostructure is constructed and its geometric structure,electronic and optical properties are studied in depth.It is found that the heterostructure can well retain the electronic structure of antimonene(Sb)and WS2(a transition metal dichalcogenide(TMD))monolayer,and a small bandgap semiconductor with type-? band alignment is realized,which will promote the separation of the lowest energy electron-hole effectively,making it possible to be applied in the field of optoelectronics.More interesting is that the external electric field(Eext)can effectively adjust the band gap(Eg)and band edge position of the heterostructure.For example,the positive Eext can make the heterostructure transition from the intrinsic type-? to the type-? and then to the type-?,while the high negative Eext can realize the transition of type-? band alignment(metal),which makes the Sb/WS2 promising to be applied in logic devices(field effect transistors(FETs)).The heterostructure always keep type-? band alignment unchangeable within a vertical strain,but the band gap can quickly become smaller,which is in favor to designing a mechanical switch.Particularly,the strong light absorption anisotropy is also found in the heterostructure,and power conversion efficiency(PCE)is up to 20.98%.Besides,the low positive Eext not only significantly improve the light absorption,but also the PCE is up to 22.845%.Which means that the heterostructure has a exceptional application prospect in the field of solar cells.Apparently,Our calculation results provide a useful reference for the experimental study of the Sb/WS2 hetero structure nanoelectronics and optoelectronic devices.Finally,the magneto-electronic properties of Sb/WS2 heterostructure adsorbed by Fe atom are calculated.We select multiple adsorption sites into three categories,and find that Tw,Ts_m and Vsb are the most stable adsorption sites,which can induce magnetism.The Tw,TS_m adsorption makes heterostructure be a HSC,while the Vsb adsorption leads to a BMS.The spin polarized charge density,the magnetic moment before and after Fe atom adsorption,and the net magnetic moment of the system indicate that the system magnetism is mainly contributed by Fe atom.The electron configuration(VEC)of Fe atoms before and after adsorption and the number of charge transfer calculated by Bader further suggest that the magnetism is mainly caused by the transfer of 4s electrons of Fe atoms into 3d and 4p orbitals and the heterostructure.The calculated magnetization energy shows that Ts_m has the highest magnetic stability,while the magnetic properties of Vsb are easily affected by thermal fluctuations at room temperature.Meanwhile,we find that the applied electric field and strain not only induce various magnetic properties of the Fe adsorption system,but also regulate the stability of structure and band gap.These results indicate that Fe adsorption of the Sb/WS2 heterostructure is of great significance in spintronics.