The electronic structures and transport properties of prototype carbon nanotube (CNT) (10,10) and boron-nitride nanotube (BNNT) (10,10) nanocables, including (VBz) n @CNT and (VBz) n @BNNT (where Bz = C 6 H 6 ), are investigated using the density functional theory (DFT) and the non-equilibrium Green's function (NEGF) methods. It is found that (VBz) n @CNT shows a metallic character while (VBz) n @BNNT exhibits a half-metallic feature. Both (VBz) n @CNT and (VBz) n @BNNT nanocables show spin-polarized transport properties, namely, spin-down state gives rise to a higher conductivity than the spin-up state. For (VBz) n @CNT, the CNT sheath contributes the metallic transport channel in both spin-up and spin-down states, while the (VBz) n core is an effective transport path only in the spin-down state. For (VBz) n @BNNT, the BNNT sheath is an insulator in both spin-up and spin-down states. Hence, the transport properties of the (VBz) n @BNNT nanocable are attributed to the spin-down state of the (VBz) n core. The computed spin filter efficiency of (VBz) n @CNT is less than 50% within the bias of À1.0 to 1.0 V. In contrast, the spin filter efficiency of (VBz) n @BNNT can be greater than 90%, suggesting that the (VBz) n @BNNT nanocable is a very good candidate for a spin filter. Moreover, encapsulating (VBz) n nanowires into either CNTs or BNNTs can introduce magnetism and the computed Curie or Neél temperatures of both (VBz) n @CNT and (VBz) n @BNNT are higher than 2000 K. These novel electronic and transport properties of (VBz) n @CNT and (VBz) n @BNNT nanocables render them as potential nanoparts for nanoelectronic applications.
We perform a comprehensive study of effects of wrapping either undoped or doped polysilane (PSi) around the outer surface of a carbon nanotube (CNT) or a boron-nitride nanotube (BNNT) using density functional theory and nonequilibrium Green’s function calculations. For CNT, because the wrapping of either undoped PSi or B-doped PSi has little effect on the electronic band structure near the Fermi surface E f, the conductivity of the wrapped CNT is still dominated by the CNT π state. This behavior is also confirmed by using the two-probe device model system with a unit cell of undoped or B-doped PSi-wrapped CNT sandwiched between two Au electrodes. For P-doped PSi/CNT, the P dopant can introduce electron donor state in the valence band. However, such a P-dopant effect is still suppressed and the conductivity is still controlled by the CNT π state based on the two-probe device computation. Contrary to CNT, the PSi-wrapped BNNT can markedly influence the band structure of the BNNT. The wrapping of either undoped or doped PSi can significantly increase the conductivity. For undoped PSi/BNNT, the valence band stems from the BNNT π state while the conduction band stems from the PSi σ state. For B-doped PSi/BNNT, B atoms introduce an electron-acceptor band just above the E f, whereas in the P-doped PSi/BNNT, P atoms introduce an electron-donor band just below the E f. For the B-doped PSi/BNNT two-probe system, the B-dopant state can participate in electron transport and exhibit a notable negative differential resistance (NDR) feature. However, for the P-doped PSi/BNNT two-probe system, the P-dopant contribution is suppressed, akin to the P-doped PSi/CNT system.
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