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

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

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

Plasmon excitations in graphitic carbon spheres measured by EELS

The determination of the physical properties of individual nanometer-size particles has made rapid progress with the availability of local probe techniques during the past years. Electron energy-loss spectroscopy in a high-resolution transmission electron microscope is one experimental tool that can give insight into the intriguing properties of such small particles. The interpretation of the experimental data of the plasmon excitations is well established in the case of isotropic particles of different geometries. For the case of anisotropic particles such as multiwall fullerenes (carbon onions), the interpretation schemes had to be reviewed. In a recent publication, we have proposed a formalism based on nonrelativistic local dielectric response theory for high-energy transmission electron microscopy electrons penetrating or passing close by an anisotropic particle [Stockli et al., Phys. Rev. B 57, 15599 (1998)]. Here we report a detailed comparison of experimental data with the excitation probabilities obtained within this formalism. We show that there is an excellent agreement between theory and experiment. In consequence, we are able to interpret the plasmon loss data of multiwall fullerenes and draw conclusions on their physical properties