We investigate experimentally the transport properties of single-walled carbon nanotube bundles as a function of temperature and applied current over broad intervals of these variables. The analysis is performed on arrays of nanotube bundles whose axes are aligned along the direction of the externally supplied bias current. The data are found consistent with a charge transport model governed by the tunneling between metallic regions occurring through potential barriers generated by a nanotube's contact areas or bundle surfaces. Based on this model and on experimental data, we describe quantitatively the dependencies of the height of these barriers upon bias current and temperature.

We investigate the effect of potassium (K) doping on the transport properties of aligned single-walled carbon nanotube fibers. The temperature dependence of the electrical resistance, the current-voltage characteristics, and the magnetoresistance vs external magnetic field of the fibers consistently show that doping enhances the metallic character of the fibers and that the response of the samples can be quantitatively explained in two thermal regimes separated by a characteristic temperature T * . At temperatures higher than T * , the data are interpreted in the framework of variable range hopping theory, suggesting that the increased conductance with potassium doping is due to the increase of the density of states, which enhances carriers hopping. For temperatures below T * , experimental evidence of fluctuation temperature-induced tunneling mechanism suggests that the doping by K atoms affects the potential barriers established between adjacent carbon nanotubes, enhancing the metallic properties of the fibers. Carbon nanotubes (CNTs) are promising materials in electronics due to the potential wide range of applicability, 1 but one difficulty foreseen for large-scale developments is the fabrication of samples having homogeneous electrical properties. Aggregates, mats, or fibers are commonly formed by CNTs having both semiconducting and metallic properties, a peculiarity which limits the spectrum of possible applications. 2At present, several techniques are under investigation in order to overcome this problem, and one specific technique consists in doping the CNT aggregate in order to increase the charge carriers density and favoring a semiconducting-to-metallic transition of the whole aggregate.3 Metallic doping by using halogen 4 and alkali atoms 5 has been successfully investigated. In this Brief Report, we show that doping a single-walled CNT (SWCNT) fiber with metallic potassium atoms improves its electrical conductance, as reported for other types of CNT aggregates. 3,6,7 Moreover, interpreting the experimental data on the basis of the current theories for disordered noncrystalline materials, we provide a quantitative model for the role played by K atoms on the electrical properties of CNT fibers.The fibers studied here have an external diameter of 100 μm and consist of aligned CNTs having a diameter of 1 nm. 8In order to generate the K doping, discrete fiber pieces are loaded in a small vial (∼20 ml volume) and loaded uncapped into a bigger flask (150 ml) capped after the addition of ∼1 g of solid potassium. The enclosed system is baked up to 120• C to melt the potassium and saturate the flask with K vapors, and the fibers are kept in contact with the K vapors for 2 h. The presence of K inside the fibers is confirmed by energy dispersive spectroscopy (EDS), which detected a change of about 13% going from the surface to the center of the fiber, while the average value of the K concentration is 33%. An electron microscope image of the fiber surface is shown in the upper inset of Fig. 1 together with the s...

A new neutron detection concept is presented that is based on superconductive niobium (Nb) strips coated by a boron (B) layer. The working principle of the detector relies on the nuclear

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