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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...

Low-dimensional carbon-based materials, in particular two-dimensional graphenic carbon structures, have been produced from single-walled carbon nanotube disruption using high-shear mixing and/or treatments in sulfonitric acid mixtures at both room and high temperature. Among other two-dimensional graphenic carbon structures, colloidal dispersions of graphenic nanoflakes have been obtained. Different structural arrangements, resulting from the reorganization of carbon because of the disruption procedures applied, were observed through selected area electron diffraction (SAED) and through reflection high-energy electron diffraction (RHEED) analyses coupled to transmission and scanning electron microscopy observations. Such combined investigations in the real and reciprocal space provided structural information at the nanoscale on the clustering of graphene layers in nanoplatelets or/and on their assembly into highly ordered (single-crystal) nanosheets. Furthermore, a different carbon phase exhibiting an orthorhombic cell with Cmma symmetry has been detected by SAED and RHEED analyses. In addition, a variety of self-assemblies of hexagonal basal planes have been observed to occur as the result of their different rotational and/or translational stacking faults. Overall, the reported results contribute to define the conditions for a controlled self-assembly of graphene-based structures with tailored dimensions, which is an important technological challenge, as their structure at the nanoscale dramatically affects their electrical properties

Conductive coatings made of template-free polymerized PEDOT/ND nanoparticles with peculiar enhancement of mechanical properties and endurance to electron damage.

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Recently, many experiments have highlighted the advantage of using polycapillary optics for x-ray fluorescence studies. We have developed a special confocal scheme for micro x-ray fluorescence measurements that enables us to obtain not only elemental mapping of the sample but also simultaneously its own x-ray imaging. We have designed the prototype of a compact x-ray spectrometer characterized by a spatial resolution of less than 100 microm for fluorescence and less than 10 microm for imaging. A couple of polycapillary lenses in a confocal configuration together with a silicon drift detector allow elemental studies of extended samples (approximately 3 mm) to be performed, while a CCD camera makes it possible to record an image of the same samples with 6 microm spatial resolution, which is limited only by the pixel size of the camera. By inserting a compound refractive lens between the sample and the CCD camera, we hope to develop an x-ray microscope for more enlarged images of the samples under test.