Some words about the Raman effect!
Briefly, the Raman scattering technique is based on the inelastic scattering of light (Raman effect) when the electromagnetic radiation interacts with the matter. Due to this interaction some photons come out from the sample with higher or lower energy than that of the in coming photons. The gain or lose in the photon energy is due to the atomic vibrations of the material that in turn depends on its symmetry properties and Raman spectrum carries out information about the material structure. When the radiation gains energy (the energy contained in vibrations are transferred to the photons) we have a process called anti-Stokes. The Stokes process is said when energy is transferred from the radiation to the vibrations. Below we describe our research lines using Raman spectroscopy as the main technique
Research topics
Resonant Raman Spectroscopy in carbon nanotubes
Raman spectroscopy is nowadays well established as a powerful
technique to characterize a variety of carbon materials including their most
famous nanostructured forms, namely fullerenes and carbon nanotubes.
Read More ...
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Temperature- and pressure-induced phase transitions studied by Raman spectroscopy
Raman scattering technique is a powerful tool for studying phase transitions (crystal-crystal, crystal-amorphous). We have been studied pressure- and temperature induced structural transformations in ferroelectric and ferroelastics materials. Read More ... |
Characterization of nanostructured materials (nanocrystals and thin films)
Luminescence of rare-earth ions in glassy host
Resonant Raman Spectroscopy in carbon nanotubes
The Raman spectra for carbon nanotubes are unique, distinctive and significantly different from those of other forms of carbons due to the reduced dimensionality of carbon nanotubes. The Raman technique has been of particular importance because it allows one to get a rich, detailed characterization (structural, vibrational and electronic) of carbon nanotubes, perhaps more than with any other available characterization technique.
The nanotube electronic structure is peculiar due to its low dimensionality
and exhibits molecular-like levels where the density of electronic states is
very high at certain energies called van Hove singularities. A very strong optical absorption takes place when the radiation energy
matches the transition between valence and conduction bands. What is
fundamental and unique is that each nanotube or alternatively each (n,m) pair
has a different set of transition values Eii. This feature labels each nanotube with a finger print and if one is able to probe someway the Eii values
is possible to identify the (n,m) structure.
By using Raman spectroscopy techniques our main results are:
- Analysis of the Stokes and anti-Stokes Raman intensities allows to determine the electronic transition energies.
- The Raman spectra at the single nanotube level allowed a deep understanding of the spectra observed in nanotube bundle samples and graphite.
- Better understanding of graphite vibrational properties
- The dispersive modes such as D-band and G'-band can be used to probe electronic structure in the phonon spectra.
- The electron-phonon matrix elements induced quantum interference effects on the resonant Raman cross section of metallic carbon nanotubes.
- Probing charge transfer effects in doped carbon nanotubes.
The nanotube electronic structure is peculiar due to its low dimensionality
and exhibits molecular-like levels where the density of electronic states is
very high at certain energies called van Hove singularities. A very strong optical absorption takes place when the radiation energy
matches the transition between valence and conduction bands. What is
fundamental and unique is that each nanotube or alternatively each (n,m) pair
has a different set of transition values Eii. This feature labels each nanotube with a finger print and if one is able to probe someway the Eii values
is possible to identify the (n,m) structure.
By using Raman spectroscopy techniques our main results are:
- Analysis of the Stokes and anti-Stokes Raman intensities allows to determine the electronic transition energies.
- The Raman spectra at the single nanotube level allowed a deep understanding of the spectra observed in nanotube bundle samples and graphite.
- Better understanding of graphite vibrational properties
- The dispersive modes such as D-band and G'-band can be used to probe electronic structure in the phonon spectra.
- The electron-phonon matrix elements induced quantum interference effects on the resonant Raman cross section of metallic carbon nanotubes.
- Probing charge transfer effects in doped carbon nanotubes.