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DOI: 10.1039/C6RA08222J (Paper) RSC Adv., 2016, 6, 44041-44049

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

Yan Shanga, Cuicui Suna, Guiling Zhang*a, Zhaodi Yanga and Xin Wang*b
aCollege of Chemical and Environmental Engineering, Harbin University of Science and Technology, Harbin 150040, China. E-mail: guiling-002@163.com
bCollege of Chemistry, Sichuan University, Chengdu, 610064, China. E-mail: wangxin@scu.edu.cn

Received 30th March 2016 , Accepted 29th April 2016

First published on 29th April 2016

Abstract

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 Neél 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.

1. Introduction

One of the most fascinating properties of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) is their ability to encapsulate substances for exploring one-dimensional (1D) hybrid nanomaterials, X@CNT, where X denotes the fillers and CNT is the carbon nanotubes. Functionality of these hybrid nanostructures can be broadened compared to that of single-component CNT or encapsulated specie due to the interplay between them. During the 1990s, research was first devoted to filling SWCNTs and MWCNTs by C60 and higher fullerenes.1–6 Later, various substances including modified-fullerenes,7–13 polymers,14,15 oxides,16–18 nanowires,19–24 single element,25–27 ionic salt,28 etc. have been successfully encapsulated inside CNTs. Concerning the filling of SWCNTs, more importantly, metallocenes, such as ferrocene, chromocene, vanadocene, cobaltocene, and ruthenocene can be introduced inside SWCNTs.29–31 The insertion occurs from the vapor phase of the sandwich-type species with formation of linear metallocene chains inside the SWCNT.29,30 These new devices offer the possibility to separate the metallocenes from the environment and hence reduce its oxidation. Additionally, encapsulation of metallocenes may give rise to novel electronic, magnetic, and conducting properties not present in neat SWCNT due to the transition metal atoms of the metallocene molecules.31 For example, the trapping of cobaltocene into SWCNT is found to induce a red-shift of the photoluminescence emission, which is attributed to the formation of localized impurity states below the conduction band of the nanotubes.29 With regard to the encapsulation of MWCNTs, most works have focused on double-walled carbon nanotubes (DWCNTs). Applications of DWCNTs have been proposed including their use in nanobearings or nanogears32–34 and as high-quality fieldemitters.35,36 In analogous works, fullerene molecules,37 crystalline iodide salts (KI, CsI, PbI2),38,39 selenium double-helices40 or cage-like molecules (H8Si8O12, H3PW12O40, [W6O19]2−)41–43 have been successfully inserted into the cavities of DWCNTs. Different from X@SWCNTs, X@DWCNTs may give rise to unique properties owing to the influence between the inter-walls of DWCNTs. Take an example, fullerenes in C60@DWCNTs can interact with the outer layer of DWCNTs, as demonstrated by Raman scattering studies.44 In addition, thermogravimetric analysis of C60@DWCNTs indicated that their thermal stability was greatly enhanced as compared to pristine DWCNTs.45

Metallocenes are well known for their intriguing physical phenomena arising from transition metals. Particularly, ferromagnetism observed in V and Bz based sandwich-like clusters (VnBzn+1)46,47 and infinite wire (VBz)n47 results in their great promise as candidates for spin-polarized transport and information storage.48–50 For such 1D systems, studies have been extended to another kind of metal–ligand complexes where the ligands being of polycyclic aromatic hydrocarbons.51,52 Theoretical studies predict that these sandwich-like wires exhibits better stability and conductivity than that of (VBz)n, and thus may be more suitable for real applications.53 Polyphenylene provides a perfect polycyclic aromatic chain for sandwiching V atoms to form 1D vanadocene arrays [V(Bz)2]n. We have reported the electronic and transport properties of the nanocables with (VBz)n in molybdenum disulfide nanotube (MoS2NT),54 CNT and boron-nitride nanotube (BNNT).55 In this work, we investigate electronic and magnetic properties of two novel nanocables by endohedral encapsulating [V(Bz)2]n inside SWCNT and DWCNT. To our knowledge, this is the first contribution for these nanocables, especially for DWCNT nanocables. Our results show that these nanocables are thermodynamically stable and their electronic and magnetic properties are tuned by the core [V(Bz)2]n.

2. Models and computational methods

Metallic SWCNT (9, 9) is selected as prototype host single-walled carbon nanotubes. For DWCNT, inner (9, 9) and outer (14, 14) tubes are used. In recent years, the coplanar low dimensional nanostructures constituted by Bz rings, e.g. graphene nanoribbons and graphene nanoflakes are under active investigations owing to their unique π-conjugated electronic structure.56 Here, we also suppose that the Bz rings in [V(Bz)2]n arrange in a coplanar orientation. For computing electronic structures, the infinite [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT systems are modeled using the periodic condition in the axial direction. For computing transport properties, the two-probe devices are adopted. As a benchmark test, we have computed electronic properties and transport properties for pure [V(Bz)2]n, SWCNT, and DWCNT systems.

For periodic systems, the supercell of [V(Bz)2]n@SWCNT contains 144 atoms of CNT and two units of V(Bz)2 (i.e., [V(Bz)2]2) (Fig. 1), and that of [V(Bz)2]n@DWCNT contains 144 atoms of inner CNT layer, 224 atoms of outer CNT layer, as well as two units of V(Bz)2. This is because that the lattice parameter of the [V(Bz)2]2 (∼9.693 Å) nearly matches the lattice parameter of the supercell of S(D)WCNT (∼9.844 Å). In addition, such a supercell containing two V atoms can be used to study magnetic coupling between V atoms. The nanocables are separated by 15 Å vacuum to neglect tube–tube interaction. All the periodic systems are fully optimized until the maximum absolute force is less than 0.02 eV Å−1.


image file: c6ra08222j-f1.tif
Fig. 1 Optimized structures of [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT. [V(Bz)2]n@DWCNT also illustrates the two-probe devices for electron transport computation.

For the two-probe devices, we take two optimized supercells as the central scatter region, i.e., [V(Bz)2]4@SWCNT or [V(Bz)2]4@DWCNT for the two-probe devices. The scatter region is long enough (>17 Å) to separate the left and right electrodes. To compute intrinsic transport properties of the nanocables, we select one supercell as each of the two opposing electrodes (Fig. 1). Transport current is computed by changing the applied bias in the step of 0.2 V in the range of −1.0 to 1.0 V.

All the computations for both infinitely long and two-probe systems are performed using density functional theory (DFT) and non-equilibrium Green's function (NEGF) methods, implemented in the software package Atomistix ToolKit (ATK).57–60 A generalized gradient approximation (GGA) within the Perdew–Burke–Ernzerhof (PBE) formalism is employed to describe the exchange correlations between electrons. Spin polarization of V atom is considered in all calculations. The on-site correlation effects among 3d electrons of V atom are accounted for by using the GGA + U scheme.60 In fact, U can be determined non-empirically,61 here we set it to be 3.5 eV for the sake of economical computations. A double-ζ basis with polarization (DZP) is used for all atoms. A (1 × 1 × 100) k-point in string Brillouin zone (x, y, z directions, respectively) is adopted, and 150 Ry cutoff energy is applied to describe the periodic wave function.

3. Results and discussions

First, we show results of geometry, magnetism, and band structures of the infinitely long nanocables of [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT, followed by transport properties computed based on their two-probe devices. The results of pure [V(Bz)2]n, SWCNT, and DWCNT are also given for comparison.

3.1. Stability and geometry

Fig. 1 shows optimized structures of [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT. Their computed total energies per supercell are listed in Table 1. The antiferromagnetic (AFM) state and the ferromagnetic (FM) state of the two V atoms are both considered. Notably, the two nanocables both favor the FM V–V coupling as reflected from the lower energy of the FM state compared to the AFM state. Hereafter, we mainly focus on the FM state of these nanocables and discuss associated electronic and transport properties.
Table 1 Calculation results for [V(Bz)2]n, [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNTa
Species ETot,FM/eV ETot,AFM/eV ΔEFM–AFM/eV ΔEr,FM/eV J/eV Tc(N)/K S/μB
a For per supercell, computed total energies in the FM or AFM state (ETot,FM, ETot,AFM), the energy difference between FM and AFM states (ΔEFM–AFM), the reaction energy in the FM state (ΔEr,FM), the exchange parameter (J), the Curie or Neél temperatures (TC(N)), and the magnetic moment (S).
[V(Bz)2]n −7874.9980 −7874.8519 −0.146 — 0.146 566.28 2.62
[V(Bz)2]n@SWCNT −30[thin space (1/6-em)]343.2364 −30[thin space (1/6-em)]342.9484 −0.288 −1.092 0.288 1115.89 2.81
[V(Bz)2]n@DWCNT −65[thin space (1/6-em)]298.5561 −65[thin space (1/6-em)]298.2329 −0.323 −1.159 0.323 1252.71 2.84

Chemical stability for encapsulated [V(Bz)2]n is evaluated by computing the reaction energy per supercell for the net reaction, S(D)WCNT + [V(Bz)2]2 → [V(Bz)2]2@S(D)WCNT − ΔEr, where S(D)WCNT represents the nanotube in a supercell. Here, the computed reaction energies ΔEr are −1.092 and −1.159 eV for [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT, respectively (Table 1). The negative values indicate exothermic reactions. Hence, incorporation of [V(Bz)2]n into SWCNT or DWCNT is energetically quite favorable.

The optimized supercell length (L) in the axial direction, the radii of the outer CNT layer (Rout), the radii of the inner CNT layer (Rin), the neighboring V–V distances (rV–V), the Bz–V distances (rBz–V), the interlayer distances between the outer and inner CNTs (rout–in), and the nearest Bz–CNT distances (rBz–CNT) for [V(Bz)2]n, SWCNT, DWCNT, [V(Bz)2]n@SWCNT, and [V(Bz)2]n@DWCNT are given in Table 2. Incorporation of the [V(Bz)2]n into S(D)WCNT causes no changes in supercell length as reflected from the identical values of L compared to the bare S(D)WCNT. The CNT outer radii Rout and the inner radii Rin of [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT are slightly expanded compared with pure SWCNT and DWCNT, respectively. The CNT interlayer distances in DWCNT and [V(Bz)2]n@DWCNT are 3.446 and 3.461 Å, respectively, suggesting a van der Waals interlayer interaction. The neighboring V–V separations in [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT are elongated by 0.076 Å comparing with bare [V(Bz)2]n. The V–Bz distances in [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT are around 1.75 Å, a little longer than that for experimental observed dimer V(Bz)2 (1.66 Å).62 The shortest distances between Bz and CNT rBz–CNT are 4.621–4.629 Å.

Table 2 Calculation geometries for supercells of SWCNT, DWCNT, [V(Bz)2]n, [V(Bz)2]n@SWCNT, and [V(Bz)2]n@DWCNTa
Species L/Å Rout/Å Rin/Å rV–V/Å rBz–V/Å rout–in/Å rBz–CNT/Å
a The optimized supercell length in the axial direction (L), the radii of the outer CNT layer (Rout), the radii of the inner CNT layer (Rin), the neighboring V–V distances (rV–V), the Bz–V distances (rBz–V), the interlayer distances between the outer and inner CNTs (rout–in), and the nearest Bz–CNT distances (rBz–CNT).
[V(Bz)2]n 9.693 — — 4.846 1.749 — —
SWCNT 9.844 — 12.718 — — — —
DWCNT 9.844 19.628 12.736 — — 3.446 —
[V(Bz)2]n@SWCNT 9.844 — 12.739 4.922 1.749 — 4.621
[V(Bz)2]n@DWCNT 9.844 19.680 12.758 4.922 1.750 3.461 4.629

3.2. Band structures

Fig. 2 displays band structure and the average projected density of states (PDOS) of each element for pure [V(Bz)2]n, together with the corresponding Kohn–Sham orbitals at the Γ point near the Fermi level (Ef). In the spin-up state, the V 3d states open a band gap of 1.87 eV, suggesting an insulation character. Evidently, in the spin-down state, a band crosses the Ef, showing a metallic character. Therefore, the [V(Bz)2]n nanowire exhibits a half-metallic property. This result is very similar to that of the vanadium–benzene multidecker nanowire (VBz)n, which is identified to be a half-metal by experimental observations46 and theoretical investigations.47–49
image file: c6ra08222j-f2.tif
Fig. 2 Computed band structures and PDOS of [V(Bz)2]n and the Kohn–Sham orbitals corresponding to the energy levels (highlighted in color lines) near Ef at the Γ point. The iso-surface value is 0.005 (e Å−3).

Fig. 3 gives the band structure and PDOS for pure SWCNT and DWCNT as well as the corresponding Kohn–Sham orbitals near the Ef. Also, Fig. 4 and 5 give the results for the nanocables [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT, respectively. For pure SWCNT, the valence band and the conduction band cross at the Ef with large dispersion, reflecting typical metallic characteristics. After encapsulating [V(Bz)2]n inside SWCNT, the spin-up state clearly shows different features from the spin-down state. Compared with pure SWCNT (Fig. 3 vs. 4), one can see that in the spin-up state of [V(Bz)2]n@SWCNT, the CNT conduction band downshifts and bestrides the Ef, while the [V(Bz)2]n does not offer a transport path. As such, the SWCNT still dominates the spin-up electron transport in [V(Bz)2]n@SWCNT. For the spin-down state, the [V(Bz)2]n band crosses the Ef. Thus, the [V(Bz)2]n contributes a metallic channel in the spin-down state of [V(Bz)2]n@SWCNT, meanwhile, the CNT still behaves as a strong metallic conductor in the spin-down state. Therefore, [V(Bz)2]n@SWCNT would exhibit strong metallic character with a little spin-polarized transport property arising from half-metallic character of core [V(Bz)2]n. These results can be reflected from the projected density of states (PDOS) as well in Fig. 4. Evidently, the SWCNT π states of [V(Bz)2]n@SWCNT exhibit similar PDOS, e.g., peaks and broad valleys around the Ef. Thus, SWCNT is still the main transport channel even with the core [V(Bz)2]n nanowire. For the spin-up state, no [V(Bz)2]n PDOS peak appears around the Ef. For the spin-down state, both the Bz π PDOS and V 3d PDOS cross the Ef with a half-filled character, manifesting the transport channel along [V(Bz)2]n.


image file: c6ra08222j-f3.tif
Fig. 3 Computed band structures and PDOS of SWCNT and DWCNT and the Kohn–Sham orbitals corresponding to the energy levels (highlighted in color lines) near Ef at the Γ point. The iso-surface value is 0.005 (e Å−3).

image file: c6ra08222j-f4.tif
Fig. 4 Computed band structures and PDOS of [V(Bz)2]n@SWCNT and the Kohn–Sham orbitals corresponding to the energy levels (highlighted in color lines) near Ef at the Γ point. The iso-surface value is 0.005 (e Å−3).

image file: c6ra08222j-f5.tif
Fig. 5 Computed band structures and PDOS of [V(Bz)2]n@DWCNT and the Kohn–Sham orbitals corresponding to the energy levels (highlighted in color lines) near Ef at the Γ point. The iso-surface value is 0.005 (e Å−3).

With regard to pure DWCNT, the valence band derives mainly from the inner layer, while the conduction band originates from both the inner and outer layers, and the valence band and conduction band intersect at the Ef. Therefore, two major transport pathways exist in DWCNT: one belongs to direct mechanism through electron transporting along inner layer, the other belongs to indirect mechanism via electron hopping form inner to outer layers, and thus DWCNT should have higher conductivity than SWDNT. This is further confirmed by the calculated currents of the two-probe devices in the following section. Clearly, introducing [V(Bz)2]n into the cavity of DWCNT can influence the band structure. In the spin-up state of [V(Bz)2]n@SWCNT, two bands which mainly come from the inner tube of DWCNT cross the Ef, suggesting that the spin-up electron transporting is mainly through the inner layer of DWCNT. Different from the spin-up state, an evident [V(Bz)2]n band crosses the Ef, behaving as an effective transport pathway. Therefore, half-metallic character of pure [V(Bz)2]n is preserved even after enclosed in DWCNT. Different from pure DWCNT, the indirect channel in the spin-up state of [V(Bz)2]n@DWCNT derives from electron hopping form outer to inner CNT layers rather than from inner to outer CNT layers. PDOS distribution in Fig. 5 also demonstrates these results. Evidently, the CNT π states contribute constant peaks around the Ef, suggesting main transport channels even with the core [V(Bz)2]n. For the spin-up state, no [V(Bz)2]n PDOS appears around the Ef, while, [V(Bz)2]n PDOS crosses the Ef in the spin-down state. Therefore, 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.

3.3. Magnetic properties

As shown in Table 1, both [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT favor the FM ground state and their magnetic moments S for each supercell are 2.81 and 2.84 μB, respectively. These values are larger than the multidecker sandwich-like (VBz)n nanowire (S = 2.0)49 and pure [V(Bz)2]n (2.62 μB). The magnetic behavior of [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT is also reflected by uneven PDOS distribution in the spin-up and spin-down states as shown in Fig. 4 and 5. The spin polarization is mainly due to the V atoms. The exchange parameter J, which can be estimated by the energy difference between AFM and FM configurations, is about 0.288 and 0.323 eV per supercell (containing two V atoms) for [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT, respectively (Table 1). We also estimate the Curie or Neél temperatures, TC(N), of the nanocables using the formula 3/2kBTC(N) = J/2 (Table 1). The estimated Curie or Neél temperatures for [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT are all higher than 1100 K, much higher than that of bare [V(Bz)2]n (566 K), suggesting that their FM state can be highly stable even at elevated temperatures. Therefore, [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT are potential candidates as magnetic nanopart.

3.4. Transport properties

To analyze the effect of core [V(Bz)2]n on the transport properties of the two nanocables, we construct a model system such that two unit cells, i.e., [V(Bz)2]4@SWCNT or [V(Bz)2]4@DWCNT, are sandwiched between two electrodes, forming two-probe device as described in Section 2 (Fig. 1). Computation results suggest that electric conductivities of the two-probe devices are consistent with the electronic structures of the corresponding infinitely long systems.

The computed I–V curves based on the two-probe devices are shown in Fig. 6. The conductivities of SWCNT, DWCNT, [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT satisfy the Ohm's law, showing typical metallic property. The magnitude of total current of DWCNT is nearly two times larger than SWCNT (Fig. 6(a)), indicating that both CNT layers in DWCNT participated in electron transporting, as suggested from the band structure. The conductivities of DWCNT and SWCNT are much higher than [V(Bz)2]n. After introducing [V(Bz)2]n inside SWCNT or DWCNT, the total currents of [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT are increased by almost a magnitude from [V(Bz)2]n. Therefore, both CNTs and [V(Bz)2]n participate in electron transporting in [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT. Fig. 7 gives the transmission spectra (TS) of [V(Bz)2]n, SWCNT, DWCNT, [V(Bz)2]n@SWCNT, and [V(Bz)2]n@DWCNT. Clearly, at 0.0 V bias voltage, the magnitudes of TS peaks are in the order of [V(Bz)2]n@DWCNT > DWCNT > [V(Bz)2]n@SWCNT > SWCNT > [V(Bz)2]n (Fig. 7(a)). Those within the bias windows at 1.0 V bias voltage also follow this sequence. Here, the bias window refers to [−V/2, V/2] (indicated by wine lines in Fig. 7(b)). Generally, only states within the bias window contribute to the current. This result again manifests: the higher conductivity of DWCNT comparing with SWCNT; the dominate role of CNTs in electron transporting; the participation of [V(Bz)2]n in electron transporting. Furthermore, the voltage potentials are also shown in Fig. 8. Clearly, for [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT, scattering of the electrons takes place upon both CNT sheaths and core [V(Bz)2]n. These results are in good agreement with the electronic structures of their infinite long systems.


image file: c6ra08222j-f6.tif
Fig. 6 (a) Total currents of [V(Bz)2]n, SWCNT, DWCNT, [V(Bz)2]n@SWCNT, and [V(Bz)2]n@DWCNT and (b) spin-polarized currents of [V(Bz)2]n, [V(Bz)2]n@SWCNT, and [V(Bz)2]n@DWCNT.

image file: c6ra08222j-f7.tif
Fig. 7 (a) and (b) Total transmission spectra of [V(Bz)2]n, SWCNT, DWCNT, [V(Bz)2]n@SWCNT, and [V(Bz)2]n@DWCNT two-probe devices at bias voltage of 0.0 and 1.0 V, respectively; (c) and (d) polarized transmission spectra of [V(Bz)2]n, [V(Bz)2]n@SWCNT, and [V(Bz)2]n@DWCNT two-probe devices at bias voltage of 0.0 and 1.0 V, respectively; the vertical wine lines in (a) and (c) refer to the Ef, and in (b) and (d) refer to the bias window.

image file: c6ra08222j-f8.tif
Fig. 8 Voltage potential at 1.0 V for two-probe devices of [V(Bz)2]n, SWCNT, DWCNT, [V(Bz)2]n@SWCNT, and [V(Bz)2]n@DWCNT.

For FM [V(Bz)2]n, [V(Bz)2]n@SWCNT, and [V(Bz)2]n@DWCNT systems, the spin-up current (I↑) and spin-down current (I↓) are computed. As expected, the spin-down states of [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT give a little higher conductivity than the spin-up state (Fig. 6(b)) owing to the half-metallic character of [V(Bz)2]n, consistent with electronic structures of their infinitely long systems. The spin-polarized transport phenomenon of [V(Bz)2]n@SWBNNT and [V(Bz)2]n@DWBNNT can be further confirmed by the TS distribution in Fig. 7(c and d). At 0.0 V bias voltage, the spin-down state of [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT shows a slightly larger TS magnitude than the spin-up state at the Ef. Similarly, under 1.0 V bias voltage, the spin-down state presents a slightly larger TS contribution than the spin-up state within the bias window.

4. Conclusions

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 [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT exhibit magnetism, stronger than reported multidecker sandwich-like (VBz)n. More importantly, the ferromagnetic state of the two nanocables is predicted to have a very high Curie or Neél temperature of over 1100 K, suggesting a potential candidate as magnetic nanopart. [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT show strong metallic character 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. The [V(Bz)2]n@SWCNT and [V(Bz)2]n@DWCNT may be achieved by organometallic coupling reaction of dissolved V(Bz)2 metal compound and V(Bz)2 halide occurred in the lumen of CNT.

Acknowledgements

SY is supported by the SF for youth reserve talent of Harbin of China (grant No. 2014RFQXJ075), the NSF of Heilongjiang Province of China (grant No. E201236), and the foundation for the department of education of Heilongjiang Province of China (grant No. 12521074). GLZ is supported by the NSFC (grant No. 51473042). ZDY is supported by scientific initial funding of National Ministry of Education for returned overseas (grant No. [2014]1685) and the NSF of Heilongjiang Province of China (grant No. LC2015005).

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