Guiling Zhang

Electronic and transport properties of carbon and boron-nitride ferrocene nanopeapods

Electronic and transport properties of novel ferrocene based carbon nanotube (CNT) and boron-nitride nanotube (BNNT) nanopeapods, including Fe(Cp)2@CNT, Fe2(Cp)3@CNT, Fe(Cp)2@BNNT, and Fe2(Cp)3@BNNT (where Cp refers as cyclopentadiene), are investigated using the density functional theory and non-equilibrium Greens function methods. Computed electronic structures of the Fe(Cp)2@CNT and Fe2(Cp)3@CNT nanopeapods suggest that their electric conductivity is primarily contributed by the CNT π channel while the electron hopping from the core Fe(Cp)2 or Fe2(Cp)3 to the sheath CNT may have some contribution to the transport properties. Encapsulating Fe(Cp)2 into BNNT is more favorable for the electron conduction, owing to the splitting of the BNNT bandgap by the Fe(Cp)2 state. In contrast, introducing Fe2(Cp)3 into the BNNT is not beneficial to the conduction due to intramolecular electron transfer within the core Fe2(Cp)3 which can cause a trap effect. Because the transport channels can be changed by the applied bias voltage, the transport properties cannot be solely predicted from the electronic structures of infinite systems alone. For computing transport properties, we use two-probe device model systems with a finite-sized nanopeapod sandwiched between two CNT electrodes. Again, we find that encapsulating either Fe(Cp)2 or Fe2(Cp)3 into CNTs has little effect on the conductivity owing to the strong metallic character of the CNT sheath. Encapsulating Fe(Cp)2 into BNNTs can notably enhance electron conducting due to electron hopping from the core Fe(Cp)2 to the sheath BNNT. Encapsulating Fe2(Cp)3 into BNNTs, however, has little effect on the electron conductivity of BNNT nanopeapods due to the trap effect of the longer guest molecules. Hence, the length of guest molecules can effectively tune electronic and transport properties of the BNNT nanopeapods.

The electronic and transport properties of (VBz)n@CNT and (VBz)n@BNNT nanocables

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 = C6H6), are investigated using the density functional theory (DFT) and the non-equilibrium Greens 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 −1.0 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 Neel 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.

Electronic and transport properties of porous graphene sheets and nanoribbons: benzo-CMPs and BN codoped derivatives

We investigate the electronic and electron transport properties of a series of 2D porous n-benzo-CMP (CMP refers to π-conjugated microporous polymer) sheets with different pore sizes n and their boron-nitride (BN) codoped derivatives, BN-n-benzo-CMPs, as well as one-dimensional (1D) porous graphene nanoribbons (p-GNRs) tailored from n-benzo-CMPs and BN-n-benzo-CMPs using density-functional theory (DFT) and the non-equilibrium Greens function (NEGF) methods. We find that the n-benzo-CMP and BN-n-benzo-CMP (n = 3, 4, 5) sheets are all semiconductors with direct band gaps (0.57–1.75 eV). Their band gap decreases with increasing pore size n. In addition, the 1D armchair and zigzag p-GNRs tailored from 2D n-benzo-CMP and BN-n-benzo-CMP (n = 3, 4, 5) sheets are all semiconductors with their band gaps ranging from 0.19 to 2.0 eV. BN codoping, pore size (n), and the width of nanoribbons (w) can all be used to tune the band gap of either 2D porous graphenes or their corresponding 1D p-GNRs. Computed current–voltage (I–Vb) curves are consistent with the semiconducting properties and suggest that both BN-3-benzo-CMPs and BN-p-3ZGNRs (w = 4) can be exploited for applications in low-dimensional electronics.

Modulating the molecular third-order optical nonlinearity by curved surface of carbon skeleton

ABSTRACT Curved π bowl compounds represent another class of the completely conjugated materials with quantum dot nature. Non-equivalent hybridisation type from rim to hub carbon atoms in curved π bowl compound triggers anisotropic physical properties. With density functional method (CAM-B3LYP) and response theory calculations, curved π bowl compounds exhibit large radial and axial component ratio for its polarisability and the second hyperpolarisability. More importantly, they possess larger effective mass second hyperpolarisability (γmass) and nondiagonal components (γxxyy) compared to C60. Except the static properties, the dispersion characters of dynamic cubic response of curved π bowl compounds have been analysed in large frequency range.

Hybrid nanobud-array structures (C24)n/MoS2 and (C24V)n/MoS2: two-dimensional half metallic and ferromagnetic materials

Two-dimensional (2D) hybrid nanobud-array structures, (C24)n/MoS2 and (C24V)n/MoS2, are designed by grafting (C24)n or (C24V)n fullerene arrays onto the surface of 2D monolayer MoS2 (ML-MoS2). Our density functional theory (DFT) computations show that the attachment of the (C24)n array onto the ML-MoS2 surface turns the 2D semiconductor (ML-MoS2) into a half metal, while the attachment of the (C24V)n array onto the ML-MoS2 surface turns the 2D semiconductor into a ferromagnetic (FM) metal. Our non-equilibrium Greens function (NEGF) computation indicates that the zigzag direction of the hybrid nanobud-array structures is more preferential for electron transport than the armchair direction. For the (C24)n/MoS2 system, the grafted (C24)n array not only can markedly increase the electron conductivity of ML-MoS2 but can also induce spin-polarized transport, that is, the spin-up state exhibits higher conductivity than the spin-down state. After placing a V atom between every two-neighboring C24 fullerenes along the zigzag direction, the conductivity is further enhanced. In contrast to (C24)n/MoS2, for (C24V)n/MoS2, the spin-down state exhibits higher conductivity than the spin-up state due to the strong contribution of the V 3d state to the spin-down state. The FM metal (C24V)n/MoS2 entails a magnetic moment of 2.3 μB per V atom. These results suggest that the 2D hybrid nanobud-array structures can be tailored as nanoelectronic parts with different electronic and transport properties by design.

Transport and Photoelectric Properties of 2D Silicene/MX2 (M = Mo, W; X = S, Se) Heterostructures

The transport and photoelectric properties of four two-dimensional (2D) silicene/MX2 (M = Mo, W; X = S, Se) heterostructures have been investigated by employing density functional theory, nonequilibrium Green’s function, and Keldysh nonequilibrium Green’s function methods. The stabilities of silicene (SiE) are obviously improved after being placed on the MX2 (M = Mo, W; X = S, Se) substrates. In particular, the conductivities of SiE/MX2 are enhanced compared with free-standing SiE and MX2. Moreover, the conductivities are increased with the group number of X, i.e., in the order of SiE < SiE/MS2 < SiE/MSe2. An evident current oscillation phenomenon is observed in the SiE/WX2 heterostructures. When a linear light illumination is applied, SiE/MSe2 shows a stronger photoresponse than SiE/MS2. The maximum photoresponse with a value of 9.0a02/photon was obtained for SiE/WSe2. More importantly, SiE/MS2 (M = Mo, W) heterostructures are good candidates for application in designing solar cells owing to the well spatial separation of the charge carriers. This work provides some clues for further exploring 2D SiE/MX2 heterostructures involving tailored photoelectric properties.

Electronic and transport properties of [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT nanocables

We have investigated electronic and transport properties of a novel form of [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT nanocables by means of DFT and NEGF methods. We find that endohedral encapsulation of [V(Bz)2]n into SWCNT or DWCNT is energetically favorable. Both nanocables exhibit strong magnetism and their ferromagnetic state is predicted to have a very high Curie or Neel temperature of over 1100 K, suggesting a potential candidate as magnetic nanopart. [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT show metallic property with a little spin dependent character: spin-down state gives a slight higher conductivity than the spin-up state due to the half-metallic character of the core [V(Bz)2]n. We also find that multiple transport channels coexist in [V(Bz)2]n@DWCNT: half-metallic channel of [V(Bz)2]n, direct main metallic channel of inner CNT, indirect hopping channel between inner and outer CNTs. Encapsulating [V(Bz)2]n into either SWCNT or DWCNT can effectively tune electronic and transport properties and these nanocables can be potentially used as functional nanodevices.