Showing papers by "S. Roth published in 2002"
TL;DR: In this article, alternating current and direct current (DC) conductivities have been measured in polymer-nanotube composite thin films for a range of concentrations of multi-wall nanotubes in two polymer hosts.
Abstract: Alternating current (ac) and direct current (dc) conductivities have been measured in polymer-nanotube composite thin films. This was carried out for a range of concentrations of multiwall nanotubes in two polymer hosts, poly(m-phenylenevinylene-co-2,5-dioctyloxyp-phenylenevinylene) (PmPV) and polyvinylalcohol (PVA). In all cases the dc conductivity σDC was ohmic in the voltage range studied. In general the ac conductivity displayed two distinct regions, a frequency independent region of magnitude σ0 at low frequency and a frequency dependent region at higher frequency. Both σDC and σ0 followed a percolation scaling law of the form σ∝(p−pc)t with pc=0.055% by mass and t=1.36. This extrapolates to a conductivity of 1×10−3 S/m for 100% nanotube content. Such a low value reflects the presence of a thick polymer coating, resulting in poor electrical connection between tubes. This leads to the suggestion that charge transport is controlled by fluctuation induced tunneling. In the high frequency regime the cond...
748 citations
TL;DR: A critical review of the literature on hydrogen storage in carbon nanostructures can be found in this paper, where the authors show a reversible hydrogen storage only for single-walled carbon nanotubes (SWNTs).
216 citations
TL;DR: In this paper, an end-to-side or endto-end heterojunction can be formed by reacting chloride terminated nanotubes with aliphatic diamine, and the peak shift in the tangential vibration mode reveals that the attached chemical functional groups can behave as either an electron donor or an acceptor, and facilitate charge transfer with the host.
Abstract: Intermolecular carbon nanotube junctions were formed by coupling chemically functionalized nanotubes with molecular linkers. An end-to-side or end-to-end heterojunction can be formed by reacting chloride terminated nanotubes with aliphatic diamine. The chemically modified nanotube mats were characterized by Raman spectroscopy. The peak shift in the tangential vibration mode reveals that the attached chemical functional groups can behave as either an electron donor or an acceptor, and facilitate charge transfer with the nanotube host. The charge transfer is also verified by transport measurements on individual end-to-side intermolecular junctions, which show diode-like behavior. The charge transfer can be attributed to amide functionality at the junction.
192 citations
TL;DR: In this article, the direct conversion of electrical energy into mechanical energy is crucial for a number of high-technology applications, such as actuator design, and the use of single-walled carbon nanotubes.
83 citations
TL;DR: In this article, the substitutional placement of boron within the lattice of carbon nanotubes yields quite different transport properties for single walled and multi-walled Nanotubes (MWNTs) as compared to MWNTs.
15 citations
TL;DR: In this article, the chemical processes connected with the so-called solid state reaction performed for doping carbon material with alkali metals (alkali metal: lithium) were studied and identified by X-ray diffraction analysis, differential scanning calorimetry and mass spectrometry.
11 citations
28 Feb 2002
TL;DR: In this paper, the Schottky barrier was formed in the contact region due to the charge transfer from the metallic tube to semiconducting tube, leading to pronounced rectifying behavior.
Abstract: Metal-Semiconductor crossed carbon nanotube junction was prepared by adsorption of carbon nanotubes on Si/SiO2 substrate with predefined electrode contacts. The Schottky barrier was formed in the contact region due to the charge transfer from the metallic tube to semiconducting tube. The charge transport was strongly modified by the formation of barrier, leading to pronounced rectifying behavior. The results were modeled using conventional thermoionic emission theory. The ideality factor in diode is 5.8 eV at room temperature and increases as raising operating temperature.
6 citations
02 Oct 2002-Structural and Electronic Properties of Molecular Nanostructures. XVI International Winterschool on Electronic Properties of Novel Materials
TL;DR: In this paper, the atomistic nature of hydrogen storage in carbon SWNTs was investigated by thermal desorption spectroscopy utilizing mass spectrometry, and the partial pressures of desorbed H2, D2 and HD have been simultaneously recorded after sample loading with a 1:1 mixture of H2 and D2 gases.
Abstract: The atomistic nature of hydrogen storage in carbon SWNTs has been investigated by thermal desorption spectroscopy utilizing mass spectrometry. The partial pressures of desorbed H2, D2 and HD have been simultaneously recorded after sample loading with a 1:1 mixture of H2 and D2 gases. The amount of desorbed HD molecules approaches the ratio 2:1:1 for HD:H2:D2 in the case of atomic storage. In the case of molecular storage the concentration of HD approaches the background level. It was found that hydrogen isotopes are stored as atoms in SWNT samples containing transition metals from either sample production (Ni, Fe, …) and/or activation (opening) process (Ni, Fe, Ti, …). Purified SWNTs store hydrogen in the molecular state, if any.
4 citations
02 Oct 2002-Structural and Electronic Properties of Molecular Nanostructures. XVI International Winterschool on Electronic Properties of Novel Materials
TL;DR: Intermolecular carbon nanotube junctions were formed by coupling chemically functionalized nanotubes with molecular linkers as discussed by the authors, leading to a metal-insulator transition.
Abstract: Intermolecular carbon nanotube junctions were formed by coupling chemically functionalized nanotubes with molecular linkers. A T‐shape heterojunction can be formed by reacting chloride terminated nanotubes with aliphatic diamine. Electronic devices were prepared by adsorption of functionalized nanotube junctions on Si/SiO2 substrate followed by standard e‐beam lithography. The charge transport through the junction was fund to be strongly modified by the in‐plane nanotube mechanically, leading to pronounced metal‐insulator transition.
1 citations
02 Oct 2002-Structural and Electronic Properties of Molecular Nanostructures. XVI International Winterschool on Electronic Properties of Novel Materials
TL;DR: In this article, a single wall carbon nanotube was used as a demonstrator of an electromechanical actuator based on an individual single-wall carbon carbon nanophore.
Abstract: Samples of individual free standing carbon nanotubes fixed on nanostructured metallic blocks have been prepared. Electrons can be injected into the nanotubes by touching the tube with a conducting AFM tip. Because of this excess charge the nanotube expands in a similar way as buckypaper does in an electrolyte. The expansion of the tube leads to a deflection of the AFM cantilever. From the experimental data the relative length change is estimated to be 1.8 × 10−5 per injected electron, in rough agreement with theoretical expectations. These findings are taken as a demonstrator of an electromechanical actuator based on an individual single wall carbon nanotube.
02 Oct 2002-Structural and Electronic Properties of Molecular Nanostructures. XVI International Winterschool on Electronic Properties of Novel Materials
TL;DR: In this paper, the hydrogen adsorption properties of the carbon nanotube materials were investigated by temperature dependent analysis of the 1H-NMR spectra, and they were produced with different kinds of catalysts and hydrogen loaded under 23 bar hydrogen pressure.
Abstract: We report proton nuclear magnetic resonance (1H‐NMR) measurements on hydrogen loaded single walled carbon nanotubes. The carbon nanotubes were produced with different kinds of catalysts and hydrogen loaded under 23 bar hydrogen pressure. The hydrogen adsorption properties of the carbon nanotube materials were investigated by temperature dependent analysis of the 1H‐NMR spectra.
28 Feb 2002
TL;DR: In this paper, single-walled carbon nanotubes are connected to superconducting electrodes with a contact resistance considerably higher than the quantum resistance of h/2e2.
Abstract: Single-Walled Carbon Nanotubes are connected to superconducting electrodes with a contact resistance considerably higher than the quantum resistance of h/2e2. For the charge transport this excludes proximity effects and/or Andreev reflections but single-charging effects should be observable. The output characteristics of these devices are different from those observed in Single-Walled Carbon Nanotubes contacted by noble metal leads within the Coulomb-Blockade regime.
02 Oct 2002-Structural and Electronic Properties of Molecular Nanostructures. XVI International Winterschool on Electronic Properties of Novel Materials
TL;DR: In this paper, the substitutional placement of boron within the lattice of carbon nanotubes can yield quite different electronic properties for (SWNT) single walled and (MWNT) multi-walled nanotsubes.
Abstract: The substitutional placement of boron within the lattice of carbon nanotubes can yield quite different electronic properties for (SWNT) single walled nanotubes as compared to (MWNT) multiwalled nanotubes. Boron “doping” of the MWNTs results in an acceptor state in the local density of states that lies near the Fermi level. While, acceptor states also occur in the case of substitutional boron doping in single walled nanotubes (SWNTs), the energy of these states relative to the Fermi level is very different. The transport properties of doped MWNTs also show striking differences with the doped SWNT case. We interpret these results as suggesting that the substitutional dopants have been introduced into the lattice of these two morphologies of nanotubes in very different ways.