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...

The firing conditions used to produce an Athenian vessel in the 5th century B.C. were determined by XANES spectroscopy.

The black and red coloration of ancient Athenian pottery is due to the different oxidation states of iron oxide: reduced Fe 2+ (black) and oxidized Fe 3+ (red). It has long been thought that a single, three-step firing -oxidation-reduction-oxidation -was used to manipulate the Fe valence state and achieve different degrees of vitrification between the slip and the body to produce the high contrast black and red images. However, complex and layered structures, with slips of different color overlaying each other, are sometimes found, raising the question of the adequacy of a single three-step firing to produce complex architectures. The firing conditions used in the production of an ancient vessel in the collection of the J. Paul Getty Museum, in which a red glossy layer is found between the black gloss and the body, were investigated. The ancient specimen was compared to a set of replicates produced and fired under a series of controlled temperatures and oxygen fugacities. Raman spectroscopy was used to identify the mineralogical phases present in both the ancient and the replicate samples, and the shape and position of the E g mode in hematite provided a measure of the temperatures at which the minerals were formed. The results suggest the ancient vessel was produced using at least two separate firings: a high temperature firing under oxidizing conditions to create the underlying red glossy layer, followed by a three-step firing to create the surface black gloss decoration. This finding suggests the firing of ancient Athenian pottery was more complex than previously thought.