Philipp Kohler-Redlich

Electrical transport in pure and boron-doped carbon nanotubes

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).

Aligned CNx nanotubes by pyrolysis of ferrocene/C60 under NH3 atmosphere

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 ...

Selective specimen preparation for TEM observation of the cross-section of individual carbon nanotube/metal junctions

We present here an efficient method to prepare a transmission electron microscopy (TEM) specimen for selective observation of the cross-section of individual nanoscale structures. As a typical example, the cross-sectional TEM observation of a quasi-one-dimensional material - a nano-electronic component based on an individual carbon nanotube - is presented.

Doping and connecting carbon nanotubes

Self-assembly pyrolytic routes to arrays of aligned CN x nanotubes are described. The electronic properties and the density of states (DOS) of these N doped tubes characterized by scanning tunneling spectroscopy (STS) are also presented. Using tight-binding calculations, we confirm that the presence of N is responsible for introducing donor states near the Fermi Level. Finally, it will be shown that high electron irradiation during annealing at 700-800°C, is capable of coalescing single-walled nanotubes (SWNTs). We investigate the merge at the atomic level using tight-binding molecular dynamics (TBMD). Vacancies induce the coalescence via a zipper-like mechanism, responsible of a continuous reorganization of atoms on individual tube lattices within the adjacent tubes. The latter results pave the way to the fabrication of nanotube contacts, nanocircuits and strong 3D composites using irradiation doses under annealing conditions.

Crystallization behavior of amorphous Fe-P strengthened with embedded carbon nanotubes

Fe80P20 amorphous alloy, amorphous Fe–P–C, and amorphous Fe–P strengthened with embedded carbon nanotubes were fabricated by the rapid solidification process. Magnetothermal analysis, high-resolution transmission electron microscopy, and x-ray diffraction were employed to investigate the crystallization behavior of these amorphous alloys. Carbon nanotubes embedded in the amorphous matrix increases the apparent crystallization temperature by about 100 K and modifies the crystallization process compared to those of amorphous Fe–P and amorphous Fe–P–C. The role of the added carbon nanotubes will be discussed.Fe80P20 amorphous alloy, amorphous Fe–P–C, and amorphous Fe–P strengthened with embedded carbon nanotubes were fabricated by the rapid solidification process. Magnetothermal analysis, high-resolution transmission electron microscopy, and x-ray diffraction were employed to investigate the crystallization behavior of these amorphous alloys. Carbon nanotubes embedded in the amorphous matrix increases the apparent crystallization temperature by about 100 K and modifies the crystallization process compared to those of amorphous Fe–P and amorphous Fe–P–C. The role of the added carbon nanotubes will be discussed.

Temperature dependence of the resistivity of individual multi-walled pure/boron doped carbon nanotubes at elevated temperatures

The resistivities of individual multi-walled pure/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 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). The activation energy derived from the resistivity vs. temperature Arrhenius plots was found to be smaller for the B-doped (58–78 meV) than for the pure multi-walled nanotubes (190–290 meV).