Theoretical Study On Defect Nano Silicon Carbide Materials With Reversible Switching Magnetic Spin Coupling Properties

The electronic properties and their relevant modulations for various defect nanoscale diamonds and their analogues are currently of profound interest due to their potential applications.As one of the third generation semiconductor,diamond-like silicon carbide(SiC)is a promising and attractive material for used in the fields of high-temperature and high-voltage semiconductor electronics and nuclear energy applications because of its inherent excellent chemical and physical stability and outstanding mechanical and thermal properties.Besides,Si vacancy(VSi)defect in SiC has great potential in quantum computing and sensing,and the formation mechanism,defect characterization and potential applications related to Vsi with internal H atoms have been widely investigated.However,the interesting phenomena that the inherent electronic properties generated by the related defects,the magnetic coupling property regulated by an applied electric field,and the magnetic spin interaction dynamics due to H-motion,are still poorly understood in the nano SiC.In order to further expand the research field of defect-induced magnetism in diamond-like materials,several kinds of C-radical nano SiC clusters containing N,B and H doped Vsi defects are designed in this paper,and the relevant density functional theory calculations are carried out.The main research results are summarized as follows.1.Magnetic couplings and applied electric field regulation in diradical SiC defect diamond-like nanoclusters.SiC has similar structural characteristics and electronic properties to diamond,but there is still a lack of research on the magnetic coupling properties of nano SiC defects currently.This work computationally investigates the magnetic coupling characteristics of SiC nanoclusters with four different types of N and B doped Vsi defect center,NV-,NNV,NBV and BBV.Our results reveal that three main modifications,surface perfluorination,layer expansion and doping N or B,can each regulate the spacing and electronic interaction in the radicals and thus determine whether they involve ferromagnetic(FM)or antiferromagnetic(AFM)coupling.The magnetic coupling essentially originates from the magnetic moments produced by the p-orbital on the C-radicals around the VSi.In particular,an applied electric field can affect the distribution and stability of an excess electron among the C-radicals in the NV-center.Detailed analyses uncover two important relationships,J ∝ I(field intensity)and |J| ∝ d(diradical spacing),which can better describe the dependence of the magnetic coupling constant J on non-intuitive variables.Under an applied electric field,when an excess electron becomes localized on one of three C-radicals from the delocalized distribution over three C-radicals,i.e.forming a carboanion(C-),the other two C-radicals with maintaining a large spacing can switch from the FM to AFM coupling.Interestingly,the two highest occupied molecular are no longer singly occupancy due to the formation of C-orbitals,while the two highest open shell ones participate in the AFM coupling.This work provides new insights into electron spin couplings for endohedrally confined multiple radicals in such SiC defect diamond analogues,and possible magnetic characteristics regulated by an applied electric field in inorganic magnetic materials and logic devices.2.Electron-coupled proton transfer(ECPT)governed magnetic spin couplings and switching in defect nano silicon carbide.H has an important impact on the related electronic properties of Vsi in SiC.This work computationally explores the magnetic coupling characteristics and dynamic behaviors induced by H-motion in nano SiC with four different types of H-doped VSi defect centers,(VSi+H)-,(VSi+H)+,(VSi+2H)and NVH.Our results reveal their unique FM or AFM spin coupling characteristics and H-motion-induced interconversion.In general,the interior H-motion goes through the electron-coupled proton transfer in a C-H…C unit which has great impact on molecular orbitals,spin densities and thus spin couplings among the C-radicals,allowing the VSi center to undergo magnetic switching between FM and AFM coupling.Interestingly,as in the(VSi+H)-center,such ECPT can further drive the excess electron delocalized on three C-radicals to gather at the ECPT unit,forming a three-center-four-electron(3c-4e)[C··H··C]-covalent H-bond with the switching of magnetic coupling,which also improve the stability of excess electron.At this time,the highest closed shell doubly occupied molecular orbitals support the H-bond orbitals,while the two next highest open shell ones support the AFM coupling orbitals.This work provides the dynamics insights into the spin coupling characteristics and its regulation by internal H-motion and multiple radical characters of such defect materials,and also provides inspired information for the design of inorganic magnetic materials and logic devices which can be controlled by interior doping and dopant dynamics.In a word,this paper mainly studies and discusses several kinds of diamond-like defect nano SiC materials with magnetic spin coupling properties in detail.In particular,two of them have a reversible switch,and the change of their inner special orbital combination may play an important role in improving the stability of magnetic coupling switching,which provides a new design idea for molecular device materials with relatively stable magnetic functions.