Theoretical Study Of The Doping Effect On The Conductivity Of CNT And BNNT Materials

Carbon nanotubes CNT and boron nitride nanotubes BNNT have attracted most scientific attention due to their extraordinary electrical, optical, thermodynamics, mechanical, and so forth properties resulting from their quasi one-dimensional nanostructure. CNT are known to be metallic or semiconducting while BNNT to be typically insulating. Recently, noncovalent modification of CNT and BNNT has attracted particular interest, because it has been commonly realized as an effective strategy to tailor their properties while still preserving nearly all of the nanotube NT intrinsic properties. However, to date, theoretical study on the electronic and transport properties of such polymer/NT nanocomposites is scarce. By combining density functional theory DFT and non-equilibrium Green’s function formalismNEGF,we calculated the transport properties of two different series of materials. The doping effect on their conductivities was discussed based on the calculated results. This work is composed of two parts: 1 Electronic and Transport Properties of(VBz)n/CNT and(VBz)n/BNNT Nanocables. 2 Electronic and Transport Properties of Polysilane/Carbon Nanotube and Polysilane/Boron-Nitride Nanotube Composites.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 refers as C6H6, are investigated using the density functional theory and the non-equilibrium Green’s function 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 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 property of(VBz)n/BNNT nanocable is 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-1.0 to 1.0 V. In contrast, the spin filter efficiency of(VBz)n/BNNT can be greater than 90%, suggesting that(VBz)n/BNNT nanocable is a very good candidate for spin filter. Moreover, encapsulating(VBz)n nanowire into either CNT or BNNT can introduce magnetism. These novel electronic and transport properties of(VBz)n/CNT and(VBz)n/BNNT nanocables render them as potential nanoparts for nanoelectronic applications.The effects of wrapping undoped and doped polysilane PSi around the surfaces of carbon nanotube CNT and boron-nitride nanotube BNNT were theoretically investigated by using density functional theory and nonequilibrium Green’s function calculations. It was found that attachment of either undoped PSi or B-doped PSi upon CNT has little effect on the band structure near the Ef. The conductivity is dominated by the CNT π state in these PSi/CNT nanocomposites. This phenomenon is preserved in the two-probe devices as one unit cell of undoped or B-doped PSi/CNT is sandwiched between two Au electrodes. In contrast, when PSi is doped by P atom, the P atom could contribute electron donor state at the valence band. However, such P contribution is suppressed and the conductivity is still controlled by the CNT π state in the two-probe devices. Different from CNT, encircling PSi onto BNNT could evidently influence the band structure. Wrapping undoped or doped PSi could increase the conductivity as compared with the pure BNNT. In the undoped PSi/BNNT system, the valence band comes from the BNNT π state, while the conduction band stems from the PSi σ state. In the B-doped PSi/BNNT, B atom introduces an electron accepter band just above the Ef, while in the P-doped PSi/BNNT, P atom provides an electron donor band just below the Ef. In the B-doped PSi/BNNT two-probe systems, the B state may participate in electron transporting and exhibit an evident NDR feature. While in the P-doped PSi/BNNT two-probe systems, the P contribution is suppressed, similar to that in the P-doped PSi/BNNT.