Buildup of Sn@CNT nanorods by in-situ thermal plasma and the electronic transport behaviors
Buildup of Sn@CNT nanorods by in-situ thermal plasma and the electronic transport behaviors
Dongxing Wang 2 3
Da Li 1 3
Javid. Muhammad 2 3
Yuanliang Zhou 2 3
Xuefeng Zhang 0 3
Ziming Wang 2 3
Shanshan Lu 2 3
Xinglong Dong 2 3
Zhidong Zhang 1 3
0 Key Laboratory for Anisotropy and Texture of Materials (MoE), School of Materials and Engineering, Northeastern University , Shenyang 110819 , China
1 Shenyang National Laboratory for Materials Science, Institute of Metal Research, International Centre for Materials Physics, Chinese Academy of Sciences , Shenyang 110016 , China
2 Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education (MoE)), School of Materials Science and Engineering, Dalian University of Technology , Dalian 116024 , China
3 Electric transport of
Monocrystal Sn nanorods encapsulated in the multi-walled carbon nanotubes (Sn@CNT NRs), were fabricated by a facile arc-discharge plasma process, using bulk Sn as the raw target and methane as the gaseous carbon source. The typical Sn@CNT NRs are 40-90 nm in diameter and 400-500 nm in length. The CNTs protect the inner Sn nanorods from oxidation. Temperature dependent I-V curve and electronic resistance reveal that the dielectric behavior of Sn@CNT NRs is attributed to the multi-wall CNTs shell and follows Mott-David variable range hopping [lnR(T)∝T−1/4] model above the superconducting critical temperature of 3.69 K, with semiconductor-superconductor transition (SST). Josephson junction of Sn/CNT/Sn layered structure is responsible for the superconducting behavior of Sn@CNT NRs.
carbon nanotubes; nanocomposite; dielectric; variable range hopping; Josephson junction
INTRODUCTION
Encapsulation of nanostructured metals in graphite layers
can protect the metallic core from oxidation. These
carbon-coated nanostructures are now attracting more
interest, due to their potential applications as functional
materials such as lithium-ion batteries, fuel cell and
electromagnetic wave absorbents [1–3]. The carbon shell
encapsulating metallic core interferes in the electronic
properties of the nanocapsules (NCs) through changing
the ratio of sp2 to sp3 of the carbonaceous species. It is
confirmed that the single-walled carbon nanotubes
(SWCNTs) or their bundles show the classical transport
properties such as Coulomb blockade, energy
quantization, Luttinger liquid characteristics and ballistic
transport [4,5]. It is usually difficult for the multi-walled
carbon nanotubes (MWCNTs) to make electrical contact
between neighbor graphite layers because the total
conductance is significantly limited by the charge carrier
transport [6]. Variable range hopping (VRH) conduction,
weak localization, resonant tunneling phenomena,
universal conductance fluctuations, or Aharanov-Bohm
oscillations of magnetoresistance, may appear or become
dominant in the electrical transport of
MWCNTs-containing systems [7,8].
Sn is a typical metal with low melting point, high
electrical conductivity, superconductivity, electrochemical
activity and favorable behaviors. Bulk Sn has a relatively
long coherence length of ξ(0) (200 nm) [9] at nanoscale.
In the range of the coherence length (0–200 nm), the
superconductive behaviors are expected to be
significantly altered, for examples, a noticeable change in
superconducting transition temperature (TC), decreased
penetration depth, an enhancement in zero-field critical
temperature, and finite residual resistance [10,11].
Coexistence of ferromagnetism and superconductivity was
also found in Sn nanoparticles (NPs) with the size in
range of 9–16 nm [12]. One-dimensional (1D)
monocrystal Sn nanowires show TC close to 3.7 K; however
both the electrical transport and the critical field are
greatly size-related [13]. It has been reported that the
superconductivity of carbon-coated Sn@C NCs will be
destroyed as the size decreases down to 40 nm. However,
it has also been demonstrated for the carbon-coated Sn
nanorods with diameter of 50 nm and length of 200 nm,
the critical magnetic field is almost 25 times higher than
that of bulk Sn [14]. Large electrical current was also
detected for MWCNTs encapsulated Sn nanowire, which
can raise a local heating and in turn suppresses the
superconductivity [15].
Electrical conduction in a nanocomposite consisting
of the conductive and the insulative phases is usually
attributed to electrical network and the percolation, in
which the continuous conducting network or tunneling
between isolated conducting particles would be
concomitant [16]. A finite conductivity is ascribed to the
inter-particles tunneling through the dielectric regime in
the absence of metallic continuum. Kubo and co-workers
[17] revealed that the energy gap between the nearest
neighboring energy level increased rapidly with reducing
the sizes of metal particles, and thus their physical
properties differ from those of bulk metals. If the discrete
gap becomes larger than the thermal energy kBT, a
pronounced quantu (...truncated)