Showing papers by "S. Roth published in 2006"

Raman spectrum of graphene and graphene layers.

Abstract: Graphene is the two-dimensional building block for carbon allotropes of every other dimensionality We show that its electronic structure is captured in its Raman spectrum that clearly evolves with the number of layers The D peak second order changes in shape, width, and position for an increasing number of layers, reflecting the change in the electron bands via a double resonant Raman process The G peak slightly down-shifts This allows unambiguous, high-throughput, nondestructive identification of graphene layers, which is critically lacking in this emerging research area

Transparent and flexible carbon nanotube/polypyrrole and carbon nanotube/polyaniline pH sensors

Abstract: Thin film Carbon Nanotube (CNT) networks are used as a conductive, transparent and flexible electrode for electrochemically depositing a conducting polymer on it, polypyrrole or polyaniline in the present work. We analyse the properties of the device as an electrochemical sensor, measuring his pH dependence by recording the open circuit potential in various buffer solutions, ranging from pH 1 to 13. The results show a good sensitivity, linearity and stability in both cases. In the case of CNT/polyaniline, it can be used simply as an optical sensor, as the colour of polyaniline changes with pH. The CNT/polypyrrole and CNT/polyaniline devices could have applications as solid state gas sensor or biosensor deposited on any shape of surface that can be transparent and flexible.

Raman active phonons of identified semiconducting single-walled carbon nanotubes.

Abstract: The resonant Raman spectra of (n, m) semiconducting single-walled carbon nanotubes, unambiguously identified from their electron diffraction patterns, have been measured. The diameter dependence of the frequency of the tangential modes with A symmetry has been obtained in the diameter range from 1.4 to 2.5 nm. The comparison between the excitation energies and the calculated transition energies allowed us to determine precisely the values of the Es33 and Es44 transition energies. Finally, in the debate concerning the dominant process at the origin of the first-order Raman scattering in single-walled carbon nanotubes (single resonance process or double resonance process), our results are well understood in the framework of a single resonance process.

Electron transport in Ar+‐irradiated single wall carbon nanotubes

Abstract: We study the effect of Ar + -irradiation on electrical transport in an individual single wall carbon nanotube (SWNT), a thin SWNT network and a thick SWNT film. The damage to SWNT structure induced by Ar + -irradiation is characterized by Raman spectroscopy. The electrical conductance both in an individual SWNT and in a thin SWNT network is strongly reduced by highly energetic Ar + ions. On contrary, a thick SWNT film exhibits an increase of its conductivity as well as of its Young modulus after irradiation.

CVD synthesis of single wall carbon nanotubes devoted to ULSI electronic applications

Abstract: We report a comparison of the behaviour of different catalysts for the ethanol-CVD growth of single-wall carbon nanotubes (SWCNTs) on thermally grown silicon dioxide on silicon substrate. The samples have been prepared by spin-coating organometallic salt (Co, Fe, Mo, Ni acetate, and their bimetallic mixtures) water solutions (ethanol solution for Mo). As grown samples have been characterized by Raman spectroscopy, Atomic Force Microscopy and Scanning Electron Microscopy. Assuming as target the growth of high quality isolated nanotubes, the ratio in Raman spectra between the intensity of the G peak and of the D peak, has been used as main parameter to evaluate the performance of the catalytic process.

Single-walled carbon nanotubes synthesized by the pyrolysis of pyridine over catalysts

Abstract: Single-walled carbon nanotubes (SWNTs) were successfully synthesized by pyrolysis of pyridine over MgO supported Fe–Mo or Co–Mo catalysts in the presence of pure H2 or a mixture of H2 and NH3 atmospheres. The average diameters of SWNTs are ∼1.5 and ∼3 nm for pure H2 and the H2 and HN3 mixture, respectively. Scanning tunneling spectroscopy (STS) studies show that the SWNTs grown in both atmospheres are doped with nitrogen substituted into the lattice in a pyridine-type structure. This results in a donor feature in the local density of states with an energy that depends on the nitrogen doping concentration.

An anelastic spectroscopy investigation of carbon nanotubes produced by the high-pressure CO method

Abstract: The anelastic spectrum of carbon nanotubes produced by the high-pressure CO method is reported for the first time in the temperature range from 10 up to 700 K A series of peaks in the elastic dissipation are ascribed to the dynamics of atomic and molecular hydrogen, the adsorption of air, the surfactant melting and to a glassy dynamics, involving either the bundles of nanotubes or the molecular groups attached to the tubes

Hydrogen Relaxation Process in HiPco Carbon Nanotubes Studied by Mechanical Spectroscopy

Abstract: The first mechanical spectroscopy experiments in HiPco carbon nanotubes from room temperature to 3 K revealed a thermally activated relaxation process at about 25 K for frequencies in the kHz range. The peak is due to the presence of a very mobile species performing about 103 jumps per second at the peak temperature. The activation energy obtained by the peak shift with frequency is Ea = 54.7 meV; the value of the pre-exponential factor of the Arrhenius law for the relaxation time, τ0 = 10-14 s, which is typical of point defect relaxation and suggests that the process is originated by the dynamics of hydrogen or by H complexes. The peak is much broader than a single Debye relaxation process, indicating the presence of intense elastic interactions in the highly disordered bundle structure. There are indications that the relaxation process is governed by a quantum mechanism.