Thermal Spin And Semi-metal Transport Research Based On Boron And Nitrogen Co-doping Zigzag Graphene Nanoribbons

Spintronics is the transfer of information by controlling the spin of electron,and thermoelectronics is the use of temperature differences to drive electric current.The research of spintronics based on the combination of spintronics and thermoelectronics provides a new idea for the design of new nanometer functional materials in the future.This method has the advantages of fast information transmission speed,low energy consumption and high integration of information storage and processing.To some extent,it breaks the limitation that the integration degree of integrated circuits is difficult to increase.Meanwhile,in spintronics,semi-metallic materials with spin polarize rate of 100% have also been widely studied and applied.Semi-metallic materials are considered as the ideal spin injection materials for future spintronics devices such as spin filter devices,spin diodes,spin triode,and so on.Based on the first-principles calculation,this paper studied the use of boron(B)atom and nitrogen(N)atom co-doped graphene nanoribbon to achieve thermal spin transport and semi-metal transport respectively,which can be divided into the following two tasks:(1)we analyzed and studied the transport properties of graphene nanoribbons and the thermal spin current transport properties of co-doped ferromagnetic graphene nanoribbons at the edges of b-n atoms.We found that in the structure of ferromagnetic eigen-zigzag graphene nanoribbon,the transmission spectrum function of electrons with different spin directions in the vicinity of Fermi energy level is always 1,which does not have the function of generating spin current.When the most edge of the structure is doped with B and N atoms respectively,the transmission spectra of electrons with different spin directions near the Fermi energy level show a crossover phenomenon similar to 'X'.When such b-n atoms are doped on the structure of the zigzag graphene nanoribbon by applying a temperature difference rather than a voltage difference,the spin-up charge flow is in the opposite direction to the spin-down charge flow,producing a spin current.In addition,further research shows that the two spintrons generate a large reverse seebeck thermoelectric potential near the Fermi energy level,and the linear variation mechanism is satisfied.Then we calculated the structure doped with two b-n atoms(2B2N)and three b-n atoms(3B3N)at the most edge respectively.It was found that as the number of b-n atoms doped increased,the seebeck coefficient value of the two atoms with opposite signs alsoincreased.More importantly,by slightly adjusting the chemical potential value of the system,the pure spin current with a charge current of zero and a spin current of non-zero can be obtained,achieving the perfect seebeck effect,which can quickly transmit information while avoiding the energy consumption of charge flow and heat emission,and improve the performance of the device.In addition,the value of the chemical potential of the obtained pure spin current will not change with the influence of temperature,which reduces the requirement of this method to generate pure spin current and enables the device to be applied to more stable environments.These findings demonstrate the feasibility of using doped impurity atoms to generate hot spin current in the ferromagnetic zigzag graphene nanoribbon.In addition,stable pure spin current can be generated under certain conditions,which has certain guiding significance for the design of graphene-based spin devices.(2)we proposed a doping system,is that BN pair was used to replace carbon atoms which is the center of zigzag graphene nanoribbon can obtain stable metal transport,the system is composed of two pieces of BN doping graphene nanoribbons is similar to the heterojunction structure,we studied the two nanoribbons,two types of connections,respectively,is made up of carbon four-member ring and six-member ring brought a nanometer carbon on the edge and bottom edge of the another nanoribbons to connect.For all connected systems,considering the different orientations of BN pairs in the two nanoribbons,they will be divided into two structures: one is the same orientations of BN pairs,known as the 'BN-BN' system;the other is the opposite orientations of BN pairs,known as the 'BN-NB' system.Through the calculation and analysis of the transport of these systems,it is found that no matter what the connection mode and structure is,as long as the orientation of BN pair is reasonably selected,we can completely ignore the influence of magnetism and obtain stable semi-metal transport.This result is caused by the spin polarization of the chemically modified nanoribbon and the spatial separation of different spin electrons on the edge of the nanoribbon.This design idea can provide good theoretical suggestions for designing spintronic devices using graphene nanoribbons.