Origin of conductivity crossover in entangled multiwalled carbon nanotube networks filled by iron

Abstract

A realistic transport model showing the interplay of the hopping transport between the outer shells of iron filled entangled multi-walled carbon nanotubes (MWNT) and the diffusive transport through the inner part of the tubes, as a function of the filling percentage, is developed. This model is based on low-temperature electrical resistivity and magneto-resistance (MR) measurements. The conductivity at low temperatures showed a crossover from Efros-Shklovski (E-S) variable range hopping (VRH) to Mott VRH in 3 dimensions (3D) between the neighboring tubes as the iron weight percentage is increased from 11% to 19% in the MWNTs. The MR in the hopping regime is strongly dependent on temperature as well as magnetic field and shows both positive and negative signs, which are discussed in terms of wave function shrinkage and quantum interference effects, respectively. A further increase of the iron percentage from 19% to 31% gives a conductivity crossover from Mott VRH to 3D weak localization (WL). This change is ascribed to the formation of long iron nanowires at the core of the nanotubes, which yields a long dephasing length (e.g. 30 nm) at the lowest measured temperature. Although the overall transport in this network is described by a 3D WL model, the weak temperature dependence of inelastic scattering length expressed as L ~T -0.3 suggests the possibility for the presence of one-dimensional channels in the network due to the formation of long Fe nanowires inside the tubes, which might introduce an alignment in the random structure. _______________________________________________________________________________________________________ *Somnath.Bhattacharyya@wits.ac.za

Resistive switching in iron-oxide-filled carbon nanotubes

“…Likewise, the work presented by Chimowa et al demonstrates that an increase in the metallic material lling content in the MWCNT results in a more weakly localized conductivity promoted by the participation of the lling in the electronic properties. 53 Considering these facts, it becomes evident that the lling strongly contributes to the electronic transport of the Fe-MWCNTs presented herein. However, our device's conductivity experiences an abrupt change in the region of $6 V, and our lled-MWCNT contains iron oxide species, which commonly present an intriguing electrical behavior.…”

“…Thus, it remains unclear as to how the lling contributes to the electronic transport on the carbon nanotube network. According to some recent studies regarding CNTs, 13,32,53 the applied electric eld increase promotes charge injection from the outermost layer down to the innermost MWCNT layer and vice versa. For pure MWCNTs, this results in a nonlinear conductivity governed by at least two different regimes dependent on the electric eld intensity.…”

Semiconducting Carbon Nanotubes Embedded in a Metallic Film for a Thermistor Device with an Adjustable Temperature Coefficient and Reduced Noise Source Activities

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Self-Assembly Prepared Millimeter Length Ferromagnetic Carbon Nanotubes with Spin Nontrivial Electronic Transport Properties

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