Spin-polarized Transport In Graphene Nanoribbons By Atomic Chains Adsorption And Doping

As a quasi-one dimension material, graphene nanoribbons are regarded asimportant materials for spintronics devices due to their superior properties. How toget spin transport is a hot topic in spintronics. In this paper, using first-principlesspin-polarized calculations, we study spin transport properties of zigzag graphenenanoribbons (ZGNRs) with the adsorption and doping of different atomic chains.In chapter one, the research progress of graphene and the electrical properties ofgraphene nanoribbons (GNRs) are described.In chapter two, the theory research methods are introduced. Firstly, we introducethe density functional theory, and then the ATK software package which based ondensity functional theory in combination with the nonequilibrium Green’s functionmethod is introduced.In chapter three, we have investigated the spin-polarized transport properties ofnonmagnetic (metallic Al and nonmetallic C) atomic chains adsorbed on ZGNRs. Wefind that the spin polarization of ZGNRs is sensitive to the adsorption sites and atomictypes of the chains. As an Al chain is adsorbed on the middle of ZGNR, the systembecomes metallic. But no spin-polarized transport arises. As the Al chain is adsorbedon the edge of ZGNR, high spin polarization is produced around the Fermi level. Thedifferent transport behaviors are originated from the fact that the edge adsorption ofAl chain breaks the magnetization symmetry of two edges while the middleadsorption of Al chain only modifies the magnetizations of two edges equally. Moreprominent spin polarization is generated as a C chain is adsorbed on the edge ofZGNR. The complete spin polarization emerges not only around the Fermi level butalso far from the Fermi level, owing to the edge states and the localized states. Theseresults indicate that one can effectively modulate the spin-polarized transports ofZGNRs through adsorbing different nonmagnetic atomic chains.In chapter four, we have studied the spin-polarized transport properties ofZGNRs doped with zigzag BN atomic chain. We find that as a BN chain is doped inthe middle site of ZGNR, the system is still a semiconductor. As the BN chain isdoped in the subedge of ZGNR, the system can be tuned to be metallic andhalf-metallic. While as the BN chain is doped in the edge of ZGNR, the systembecomes metallic. The BN chain doping can induce a wide range of complete spin polarization for all the doping positions. The spin polarization is due to the edge statesof ZGNR and the interaction between the BN chain and adjacent C chains.In the fifth chapter, a final conclusion is given for our studies and we describethe problems for future investigations.