Yan Shang

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.

Theoretical study on the reaction of triallyl isocyanurate in the UV radiation cross-linking of polyethylene

Herein, a theoretical investigation on the reaction of triallyl isocyanurate (TAIC) in the UV radiation cross-linking process of polyethylene is conducted at the B3LYP/6-311+G(d,p) level for the production of high voltage cable insulation materials, where the reaction potential energies of 10 reaction channels are identified. The HOMO–LUMO energy gaps, ionization potentials, and electron affinities of the raw materials, product, and by-product in polyethylene insulation composite products are obtained. Furthermore, the optimized process for the production of UV radiation cross-linking polyethylene insulation materials for high voltage cables is described. The results indicate that the UV radiation cross-linking reaction of polyethylene is initiated by benzophenone, and the multi-functional cross-linker TAIC is required for the cross-linking process to occur. This investigation is expected to provide reliable information for the optimization of the polyethylene UV radiation cross-linking process and the development of insulation materials for high-voltage cables that can withstand more than 500 kV in real applications.

Theoretical study on the tailored side-chain architecture of benzil-like voltage stabilizers for enhanced dielectric strength of cross-linked polyethylene

A theoretical investigation on the mechanism of the tailored side-chain architecture of benzil-like voltage stabilizers for enhanced dielectric electrical breakdown strength of cross-linked polyethylene at the atomic and molecular levels is accomplished. The HOMO–LUMO energy gaps, the ionization potentials, and the electron affinities at the ground states of a series of benzil-like molecules are obtained at the B3LYP/6-311+G(d,p) level. The 8 isomerization reactions at the S0 state, including the harmonic vibration frequencies of the equilibrium geometries and the minimum energy paths (MEP) found using the intrinsic reaction coordinate (IRC) theory, are obtained at the same level. The substituent group effect, functional group effect, and electronic effect of the different heteroatoms (O, N, S) in substituent groups have been evaluated. The results show that benzil-like molecules, which have much smaller HOMO–LUMO energy gaps, much lower ionization potentials, and much larger electron affinities than those of aliphatic chains, can increase the electrical breakdown strength effectively as voltage stabilizers in cross-linked polyethylene. This result is consistent with Jarvid’s suggestions (Journal of Polymer Science, Part B: Polymer Physics, 2014, 52(16): 1047–1054).

Theoretical study on the reaction mechanism in the UV radiation cross-linking process of polyethylene

A theoretical investigation on the benzophenone-initiated UV radiation cross-linking reactions of polyethylene is accomplished at B3LYP/6-311+G(d,p) level for high-voltage cable insulation materials. The reaction potential energies of 9 reaction channels are identified in the T1 state. The HOMO–LUMO energy gaps, ionization potentials, and electron affinities of the polyethylene, photoinitiator, voltage stabilizer, antioxidant, and by-products in the polyethylene insulation composite products are obtained. The results show that the by-products, photoinitiator, voltage stabilizer, and antioxidant can effectively increase the electrical breakdown strength. In addition, aromatic ketone voltage stabilizer and hindered phenol antioxidants of the studied molecule can be grafted to the polyethylene chain easily during the polyethylene UV radiation cross-linking process, and they have excellent compatibility with the polymer matrix. The investigation is expected to provide reliable information for optimizing the polyethylene UV radiation cross-linking process and for the development of insulation material for high-voltage cable for use at voltages exceeding 500 kV in real applications.

Theoretical study of OCCHCN as a potential alternative insulation gas for SF6

Cyanoketene (OCCHCN) has been reported as a potential alternative insulation gas for SF6 in Patent US0135817. Stationary point equilibrium geometries on the ground state have been optimized at the B3LYP/6-311+G(d,p) level, and the harmonic vibration frequencies are calculated at the same level. The HOMO-LUMO energy gaps (Eg), ionization potentials (IP), and electron affinities (EA) of the studied molecules are obtained. The minimum energy path (MEP) is obtained by the intrinsic reaction coordinate (IRC) theory, and the energetic information is further refined by QCISD(T) (single-point) method. The results show that OCCHCN can be used as SF6 alternative insulation gas in high voltage equipment according to potential energy surface analysis. As the isomerization and the cleavage reactions potential barriers are lower than the Eg and IP values, resulting in OCCHCN is not easy to be ionized and excited.

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.

Transport properties of nanowires with alternating organosilanylene and oligoethenylene units

Transport properties of a series of σ–π-conjugated nanowires nSix(C=C)y (xxa0=xa02–4, yxa0=xa01–4, and nxa0=xa02–4) were studied by using non-equilibrium Green’s function formalism with density functional theory. It is found that the silanylene moiety length, the ethenylene moiety length, and the whole molecular length play important roles in governing the transport properties of the nanowires: (1) the conductivity tends to be decreased with increasing the silanylene moiety length x; (2) lengthening the ethenylene moiety y is not always favorable to enhancing the conductivity; (3) the zero-bias conductance is decayed exponentially with the whole molecular length n. Further analysis indicates that the conductivities correlate well with the transmission spectra and the topology of the HOMO and LUMO states.