16 research outputs found
Thermodynamic calculations on the catalytic growth of multiwall carbon nanotubes
We have developed a thermodynamic model of the catalytic growth of multiwall
carbon nanotubes from hydrocarbon precursors at elevated temperature. Using
this model we have computed the heat distribution, and carbon concentration in
the catalyst. Calculations delivered a analytical formula for the growth time
and growth rate. We find that the growth is mainly driven by a concentration
gradient within the catalyst, rather than a temperature gradient.Comment: 9 pages, 3 figures, 1 tabl
Raman spectroscopy and field emission measurements on catalytically grown carbon nanotubes
We used microcontact printing to pattern a silicon surface with an
iron-containing catalytic solution. Multi-wall carbon nanotubes were
subsequently grown on the patterned areas by chemical vapor deposition at
temperatures between 650 and 1000C. We demonstrate that the diameter of the
catalytically grown multi-wall nanotubes increases with the deposition
temperature. Raman spectroscopy has been used to investigate the crystalline
character of the obtained structures and it is found that the fraction of the
nano-crystalline shell increases with the temperatures. The measurement of the
field emission properties shows a correlation between the tube diameter and the
emission field values.Comment: 6 pages, 6 figures, 1 tabl
Plasmon excitations in graphitic carbon spheres
©1998 The American Physical Society. The electronic version of this article is the complete one and can be found online at: http://link.aps.org/doi/10.1103/PhysRevB.57.15599DOI: 10.1103/PhysRevB.57.15599Electron energy loss spectroscopy in a high-resolution transmission electron microscope has recently been used with success to characterize the electronic properties of closed cage nanometer-size graphitic particles. In the plasmon region, the experimental data reveal interesting size-dependent variations, which are not yet fully understood. The difficulties encountered in the interpretation of the spectra are principally due to the lack of a complete theoretical treatment of the anisotropic dielectric response in nanometer-size particles. In order to obtain a better understanding of the experimental data we propose a model based on nonrelativistic local dielectric response theory for electrons penetrating through a nested concentric-shell fullerene or the so-called ‘‘carbon onion.’’ The anisotropy of the electronic properties of the sphere is taken into account via the frequency-dependent dielectric tensor of graphite. The model can be applied to simulate electron energy loss spectra as well as line scans through energy filtered images and allows thus a direct comparison to experimental data
Collective oscillations in a single-wall carbon nanotube excited by fast electrons
©2001 The American Physical Society. The electronic version of this article is the complete one and can be found online at: http://link.aps.org/doi/10.1103/PhysRevB.64.115424DOI: 10.1103/PhysRevB.64.115424Electron energy loss spectroscopy is a well adapted tool for the investigation of the valence excitations of individual nanometer-size particles. The interpretation of the loss spectra of such small particles, however, relies in most cases on a quantitative comparison with simulated excitation probabilities. Here we present a formalism developed for the interpretation of the energy loss data of single-wall carbon nanotubes based on the hydrodynamic theory of plasmon excitations by high-energy electrons. The nanotubes are modeled as a two-dimensional electron gas confined on the circumference of a cylinder. The plasmon excitation probabilities, directly comparable to measurements, are discussed for various parameters
Plasmon excitations in carbon onions: Model vs. measurements
©1998 American Institute of PhysicsNon-relativistic local dielectric response theory has proven successful in the interpretation
of Electron Energy Loss data of nanometer-size isotropic particles of different
geometries. In previous work, we have adapted this model to take into account anisotropy as
encountered in the case of carbon onions. We have shown that this anisotropy needs to be
taken into account since important deviations with respect to an isotropic model can be
observed. In this contribution, we report on the first energy filtered images of carbon onions
and compare intensity profiles across the spheres to our calculations
Comparative study of the catalytic growth of patterned carbon nanotube films
Three different catalysts (Fe, Ni, Co nitrates dissolved in ethanol) were
patterned on a SiO2/Si substrate and multi-wall carbon nanotubes were grown by
catalytic decomposition of acetylene. We compare the growth of the carbon
nanostructures in the temperature range between 580C and 1000C. With our
experimental set-up the catalyst solutions of cobalt and nickel were found to
be less efficient than the one of iron. An optimal production of multi-wall
nanotubes was observed at temperatures between 650C and 720C with the iron
solution as catalyst. We found a tendency towards thicker structures with
higher temperatures. Finally, we suggest a mechanism for the growth of these
carbon structures.Comment: 5 pages, 5 figure
The Physicist's Guide to the Orchestra
An experimental study of strings, woodwinds (organ pipe, flute, clarinet,
saxophone and recorder), and the voice was undertaken to illustrate the basic
principles of sound production in music instruments. The setup used is simple
and consists of common laboratory equipment. Although the canonical examples
(standing wave on a string, in an open and closed pipe) are easily reproduced,
they fail to explain the majority of the measurements. The reasons for these
deviations are outlined and discussed.Comment: 11 pages, 10 figures (jpg files). Submitted to European Journal of
Physic
Valence excitations in individual single-wall carbon nanotubes
©2002 American Institute of Physics. The electronic version of this article is the complete one and can be found online at: http://link.aip.org/link/?APPLAB/80/2982/1DOI:10.1063/1.1469685We report on measurements of the plasmon losses of individual single-wall carbon nanotubes by electron energy-loss spectroscopy in a high-resolution transmission electron microscope. The experimental data are compared to simulated excitation probabilities calculated using the hydrodynamic theory of the interaction between a probe electron and a two-dimensional quasifree electron gas confined on a cylindrical shell. Depending on the nanotube geometry, the first- or the second-order oscillation mode dominates the loss spectrum. The resonance energy of the dominant resonance mode is found to depend on the radius of the nanotube