Investigation of electrical transport in hydrogenated multiwalled carbon nanotubes

Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA 02115, USA
Physica B Condensed Matter (Impact Factor: 1.32). 02/2011; 406(4):841-845. DOI: 10.1016/j.physb.2010.12.009


Highly disordered multiwalled carbon nanotubes of large outer diameter (∼60 nm) fabricated by means of chemical vapor deposition process inside porous alumina templates exhibit ferromagnetism when annealed in a H2/Ar atmosphere. In the presence of an applied magnetic field, there is a transition from positive to negative magnetoresistance. The transition may be explained in terms of the Bright model for ordered and disordered carbon structures. Additionally, temperature dependent electrical transport experiments exhibit a zero-bias anomaly at low temperature.

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    • "In contrast to graphite and in spite of theoretical predictions on the possibility to have magnetic order due to hydrogen or vacancies in carbon nanotubes (CNT) [3] [4] [5], the observation of this phenomenon in these carbon structures appears to be more difficult. Apparently, only the hydrogenated CNT prepared in [6] [7] showed the existence of magnetic order at room temperature. However, and in clear contrast, several studies reported the existence of superconductivity through measurements in single nanotubes as well as bundles of them (single-and multiwall) [8– 15]. "
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    ABSTRACT: The magnetotransport properties were studied in hundreds of micrometer length double-wall carbon nanotubes (DWCNT) bundles. Above 15 K the resistance shows an ohmic behavior and its temperature dependence is well described using the variable-range hopping for one-dimensional system. The magnetoresistance is negative and can be explained using an empirical model based on spin-scattering processes indicating the existence of magnetic order up to room temperature. At temperatures between 2 K and 15 K the resistance is non-ohmic and the current-voltage characteristics reveal the appearance of a potential, which can be well described by a fluctuation-induced tunneling conduction model. In this low temperature range and at low enough input current, a positive magnetoresistance appears - in addition to the negative one - with an extraordinary hysteresis in field and vanishes at $T \sim 15 $K, suggesting the existence of a superconducting state. Magnetization results partially support the existence of both phenomena in the DWCNT bundles.
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    ABSTRACT: This study presents the design and fabrication of carbon nanotubes (CNTs) film based temperature sensor. The sensor has been fabricated by the sequential deposition of thin layers of glue and CNT nanopowder on a paper substrate. The diameter of multiwalled nanotubes (MWNTs) varied between 10 and 30nm. The ostensible thickness of the CNT films in the samples was ∼30–40μm. The inter-electrodes distance (length) and width of the surface-type samples were 5 and 4mm, respectively. The results revealed that the DC resistance of the sensors decreases in average by 10–20% as the temperature increases from 20 to 75°C. The resistance–temperature relationship was simulated.
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    ABSTRACT: By applying the nonequilibrium Green function method, we have theoretically investigated the quantum transport properties of armchair and zigzag graphene nanoribbons (GNRs), with defects (vacancies) appearing at the edges or in the inner part. Effects of the defects on the electronic conductance and local density of states are comprehensively studied. It is found that both edge and inner defects reduce the electronic conductance in general, while in detail they have different effects on the transport properties for different combinations of defect location and GNR edge type. Under the same theoretical framework, we have also studied the effects of dephasing scattering processes in the GNRs, employing two specific choices of self-energy that provide momentum-conserving or momentum-relaxing dephasing processes. The momentum-relaxing dephasing processes not only relax momentum but also add an additional resistance to the channel, while the momentum- conserving dephasing processes only break the phase and have much less effect on the resistance. It is found that the transport properties of metallic zigzag GNRs are much more strongly modified by the dephasing scattering processes than are those of semiconducting armchair GNRs.
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