Theoretical exploration of the half-metallicity of graphene nanoribbons/boron nitride bilayer system

The geometrical and electronic structures as well as stabilities of zigzag GNR (ZGNR) stacked on zigzag BN nanoribbon (ZBNNR) or BN sheet have been theoretically studied at the DFT-LDA level for the first time. It is shown that the most stable structure for 4-GNR/5-BNNR is AB (boron) stacking configuration with equilibrium distance at 0.320 nm and formation energy (E_f) at -605.39 meV. At the same time, the ZBNNR changes the ZGNR from spin-degenerated semiconductor to spin-polarized semiconductor with the up- and down-spin gaps of 0.38 and 0.28 eV, respectively, due to the spontaneous polarization of ZBNNR. Most importantly, we found that the band structures of ZGNR on ZBNNR or BN sheet can be tuned into half-metal simply by two methods including applying appropriate vertical electric field and interlayer compression due to the enhanced interlayer polarization and significant changes in the charge densities at the edge atoms of ZGNR. Correspondingly, the calculated critical electric fields from semiconductor to half-metal are 2.11 and 1.70 V/nm for 4-GNR/5-BNNR and 4-GNR/BN sheet, respectively, which are smaller than that of 2.31 and 1.80 V/nm for the ZGNRs sandwiched between BNNRs or BN sheets at the same PWC/DNP level of theory. Note that the interaction between ZGNRs and ZBNNRs can be significantly enhanced under the appropriate vertical electric field. The calculated critical interlayer distance of compression-induced semiconductor-to-half metal transition for 4-GNR/5-BNNR is 0.245 nm. Moreover, it is shown that the wider stacking system can realize its half-metallicity more easily. These findings may provide new ways in fabricating new spintronic devices that are compatible with the current technology of the semiconductor industry, and may be helpful for the synthesis of nanoelectronic devices experimentally.