A New Kind of Edge-Modified Spin Semiconductor in Graphene Nanoribbons

Despite their rich electronic and magnetic properties, the freestanding or suspending zigzag edge graphene nanoribbons with n chains (n-ZGRNs) can be twisted quite easily and buckle, which makes it difficult for nanoelectronics as well as spintronics applications. Using first principles density functional theory (DFT) calculations as well as classical molecular dynamic (MD) simulations, we propose a way to overcome this problem by modifying one edge of n-ZGRNs with (m,m)single-walled carbon nanotubes ((m,m)SWCNTs) into functionalized n-ZGRNs, namely nZGNR-(m,m)SWCNTs. DFT calculations indicate that the 8ZGNR and (6,6)SWCNT are predicted to form a 8ZGNR-(6,6)SWCNT without any obvious activation barrier. Moreover, the formed 8ZGNR-(6,6)SWCNT is more energetically favorable by about 1.86 eV. Hence, the nZGNR-(m,m)SWCNT should be found in experiment under mild conditions. MD simulations indicate that the nZGNR-(m,m)SWCNT possesses significantly improved mechanical and thermal stability as compared to a n-ZGNR, such that even at 1000 K the 6ZGNR-(6,6)SWCNT can remain straight. Excitingly, we find that one edge modification with (m,m)SWCNT transforms the n-ZGNR into a ferromagnetic spin semiconductor. By simulation field-effect transistor (FET) doping, we demonstrate that in a nZGNR-(m,m)SWNT FET completely spin-polarized currents with reversible spin polarization can be created and controlled simply by applying a gate voltage. These findings should open a viable route for efficient spin-resolved band engineering in graphene-based devices with the current technology of the semiconductor industry. Finally, the origins of its unique electronic and magnetic properties as well as of its mechanical and thermal stabilities are discussed by using the band structures, partial charge densities of the bands at the Gamma and X points, Mulliken charge analysis, as well as atomic configurations.