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The resistivities of individual multiwalled pure and boron-doped carbon nanotubes have been measured in the temperature range from 25 to 300 °C. The connection patterns were formed by depositing two-terminal tungsten wires on a nanotube using focused-ion-beam lithography. A decrease of the resistivity with increasing temperature, i.e., a semiconductor-like behavior, was found for both B-doped and pure carbon nanotubes. B-doped nanotubes have a reduced room-temperature resistivity (7.4×10−7–7.7×10−6 Ωm) as compared to pure nanotubes (5.3×10−6–1.9×10−5 Ωm), making the resistivity of the doped tubes comparable to those along the basal plane of graphite. The activation energy derived from the resistivity versus temperature Arrhenius plots was found to be smaller for the B-doped (55–70 meV) than for the pure multiwalled nanotubes (190–290 meV).

teresis loop compared to that observed for particles in powder form.In this communication, synthesis of 10.7 nm ferrite nanocrystals doped with 3.5 % in mass of cobalt ions is described. Organization of nanoparticles is controlled by the method of deposition on a substrate. In an applied magnetic field, deposition leads to formation of well-aligned nanoparticles on a very large scale forming a flat surface. In the absence of an applied field, the particles self-arrange on the substrate by forming large spheres with a large coverage. Magnetic properties of nanocrystals differing by their organizations are presented: when particles are aligned, the hysteresis loop is straightened and the magnetic parameters such as remanence and coercivity notably increase. These changes in the magnetic properties are related to the demagnetizing factor and to the orientation of the magnetic moments of the particles along one of the easy magnetization axes.

Aligned CNx (x<0.1) nanotubes have been generated by pyrolyzing ferrocene/C60 mixtures at 1050 °C in an ammonia atmosphere. The structure and composition of the product were determined by high-resolution transmission electron microscopy and high spatial resolution electron energy-loss spectroscopy. The CNx tubes (15–70 nm diameter, <50 μm length) grown in large flakes (<3 mm2) consist of a reduced number of “graphitic” layers (<15 on either side) arranged in a bamboo-like structure. Areas of high nitrogen concentration were found within curved or corrugated “graphite-like” domains. The observation of a well-developed double peak in the σ* feature of the N K-edge suggests that the material has not undergone the transition to the fullerene-like phase known for nitrogenated carbons. Incorporation of nitrogen from the gas phase (NH3) into CNx nanotubes therefore leads to improved and more efficient N substitution into the network as compared to the synthesis with solid nitrogen-containing precursors reported earlier.