Showing papers by "S. Roth published in 2003"
TL;DR: In this paper, the authors revisited important experiments on the storage capacities of hydrogen in carbon nanostructures and showed that carbon nanotubes at around room temperature cannot store the amount of hydrogen required for automotive applications.
165 citations
TL;DR: In this article, the state of the art of hydrogen storage in carbon nano-structures is reviewed and new results obtained in a joint project sponsored by the Federal Ministry for Education and Research in Germany (BMBF).
121 citations
TL;DR: Atomic resolution images of multiwalled boron nitride nanotubes have been obtained using scanning tunneling microscopy operating at tunneling currents below 20 pA and biases of approximately −2.5 V as mentioned in this paper.
Abstract: Atomic resolution images of multiwalled boron nitride nanotubes have been obtained using scanning tunneling microscopy operating at tunneling currents below 20 pA and biases of approximately −2.5 V. Lattice images acquired with negative sample biases exhibit trigonal symmetry that is interpreted as resulting from nitrogen states. Tunneling spectroscopy confirms band gaps between 4.5 eV and 4.8 eV for tube diameters above 5 nm. Tunneling barrier height measurements made using standard current–distance analysis yields Φ∼6.3±0.7 eV for the boron nitride nanotubes.
44 citations
TL;DR: In this paper, single-walled carbon nanotubes (SWNTs) produced by the high pressure CO disproportionation (HiPCO) method and purified by controlled thermal oxidation in air have been studied by Raman spectroscopy at 300 and 5 K.
42 citations
TL;DR: In this paper, boron-doped multi-walled carbon nanotubes deposited on top of predefined electrode patterns have been performed to investigate the conductance properties of charge transport.
Abstract: Electrical transport measurements on boron-doped multiwalled carbon nanotubes deposited on top of predefined electrode patterns have been performed. The temperature dependence of the conductance reveals through two-point configuration, the appearance of a zero-bias anomaly which was found to be not compatible with the existence of a Luttinger-liquid-like state in the doped multiwalled carbon nanotubes. The experimental findings indicate that, in order to properly interpret the charge transport properties of multiwalled carbon nanotubes, the doping as well as the energy window in which the experiments are performed are crucial points.
35 citations
TL;DR: In this article, the first low temperature measurements of I-V characteristics of polyacetylene nanofibers were reported, which are signatures of a novel conduction mechanism: the creation of charged soliton-antisoliton pairs by quantum-mechanical tunneling.
21 citations
TL;DR: In this paper, the optical spectra of carbon nanotubes in the infrared region is used to calculate the diameter distribution and to estimate the ratio between metallic and semi conducting tubes as well.
17 citations
23 Oct 2003
TL;DR: In this article, a diameter-dependent oxidative etching of HipCO nanotubes (diameters 8-10 A) was observed by in situ Raman measurements both in a laser beam with a variable power density and in an optical oven with variable temperature.
Abstract: A diameter‐dependent oxidative etching of the smallest HipCO nanotubes (diameters 8–10 A) has been observed by in situ Raman measurements both in a laser beam with a variable power density and in an optical oven with a variable temperature. The effect manifested itself as an irreversible disappearance of the Raman breathing modes with frequencies > 220 cm−1. The small tube degradation (up to their complete disappearance) took place at temperatures 150–400°C. Statistical averaging of HRTEM images of HipCO nanotubes, taken after successive temperature steps, has confirmed an obvious shift of the tube diameter distribution maximum toward higher values.
7 citations
TL;DR: In this article, a simple model is considered to describe single-particle tunneling into a Luttinger-liquid-like state from electrically weak connected superconducting electrodes.
Abstract: Electrical transport through single-walled carbon nanotubes with weak electrical coupling to superconducting leads has been studied theoretically and experimentally. A simple model is considered to describe single-particle tunneling into a Luttinger-liquid-like state from electrically weak connected superconducting electrodes. This involves the superconductor's quasiparticle and the Luttinger liquid's excitation density of states. Experimentally, the suppression of quasiparticle tunneling induced current peaks was observed at temperatures below 0.1 K, which we attributed to the Luttinger-liquid-like excitation spectrum of the single-walled carbon nanotube.
6 citations
23 Oct 2003
TL;DR: Aqueous solutions of HiPCO SWNT with different surfactants (anionic (SDS), cationic (CTAB) and non-ionic (Triton X‐100)) have been studied by Raman and Near-infra-red (NIR) absorption spectroscopy.
Abstract: Aqueous solutions of HiPCO SWNT with different surfactants (anionic (SDS), cationic (CTAB) and non‐ionic (Triton X‐100)) have been studied by Raman and Near‐infra‐red (NIR) absorption spectroscopy. The nanotube interaction with surfactant leads to the spectral shift of lines and its intensity redistribution, compared with the spectrum of SWNT in KBr pellet. The most essential spectral changes are observed for nanotube aqueous solution with the surfactant containing a charge group. Two possible models of micelle formation around the nanotube are discussed.
6 citations
TL;DR: In this article, a scanning force microscope (SFM) is used for a single-step additive process to pattern a conductive trace on an insulating surface, where a bias voltage is applied between the conducting cantilever/tip and the pre-patterned electrodes of the sample, resulting in the formation of conductive deposits at the tip location.
TL;DR: In this article, the authors report on proton nuclear magnetic resonance (1 H-NMR) experiments on high-pressure hydrogen loaded single walled carbon nanotubes (SWNT).
23 Oct 2003
TL;DR: In this article, the transformation of single-walled carbon nanotubes into diamond by ab initio calculations and high pressure and temperature experiments was studied and the formation of hexagonal diamond as a high pressure nanotube phase was predicted.
Abstract: We studied the transformation of single‐walled carbon nanotubes into diamond by ab‐initio calculations and high‐pressure and temperature experiments. From the calculations we predict the formation of hexagonal diamond as a high‐pressure nanotube phase. High‐resolution TEM pictures of single‐walled carbon nanotubes subjected to 9 GPa and 700°C clearly indicate the formation of hexagonal diamond grains.
TL;DR: In this paper, the dependence of the electrical transport through the carbon nanotubes on magnetic field strength and direction, and on source-drain-voltage is investigated in a magnetic field applied perpendicularly to the Single-Walled Carbon Nanotubes longitudinal axis.
23 Oct 2003
TL;DR: In this paper, atomic force microscopy (AFM) investigations were done on individual suspended single-walled carbon nanotube (SWNT) bundles, showing the possibilites and limits of this technique.
Abstract: Electrochemical double layer charge injection in macroscopic sheets of carbon nanotubes (buckypaper) has been shown to convert electrical energy into mechanical energy. We investigate actuation for single nanotube bundles in order to obtain understanding that may be important for optimizing nanotube arrays (like buckypaper), understanding mechanical effects in electric devices made from nanotubes, and possibly using individual nanotubes as nanoscale actuator devices. Atomic Force Microscopy (AFM) investigations were done on individual suspended single‐walled carbon nanotube (SWNT) bundles, showing the possibilites and limits of this technique.
TL;DR: In this article, the density of states at the Fermi level were determined for pristine, lithium and cesium intercalated carbon nanotubes and discussed in terms of intercalation and charge transfer effects.
Abstract: Lithium intercalted carbon nanotubes have attracted considerable interest as perspective components for energy storage devices. We performed 13C Nuclear Magnetic Resonance spin lattice relaxation measurements in a temperature range from 4 K up to 300 on alkali intercalated Single Walled Carbon Nanotubes in order to investigate the modifications of the electronic properties. The density of states at the Fermi level were determined for pristine, lithium and cesium intercalated carbon nanotubes and are discussed in terms of intercalation and charge transfer effects.