Theoretical Study of the Raman Spectra of C₇₀ Fullerene Carbon Peapods

Abstract

International audienceThis work focuses on the hybrid system between C70 and a carbon nanotube (C70 peapod) where the encapsulated C70 peas and the nanotube pod are bonded through van der Waals interactions. The nonresonant Raman spectra of these nanomaterials were calculated in the framework of the bond-polarizability model combined with the spectral moment method. The optimal configurations of C70 molecules are derived using a convenient Lennard-Jones potential. We find that increasing the nanotube diameter leads to three successive configurations: lying, tilted, or standing alignments of C70 molecules along the nanotube axis. The changes of the Raman spectra as a function of the configuration of the C70 molecules inside the nanotubes are identified. The nanotube chirality and diameter effects on the Raman-active modes in peapods with different C70 filling factors are studied. This workprovides benchmark theoretical results to understand the experimental Raman spectra of C70 fullerene peapods

Structural and Vibrational Properties of C60 and C70 Fullerenes Encapsulating Carbon Nanotubes

“…These results indicate that only one type of orientation can exist for a given nanotube and confirm that the C 70 alignment is associated with the geometrical parameters of the nanotube host. Theoretical studies showed that the configuration of C 70 s inside SWCNT depends primarily on tube diameter and does not significantly depend on tube chirality [21,22]. In order to obtain the optimal structure of the C 70 inside the nanotubes, an energy minimization procedure was performed by Fegani et al (for more detail, see reference [21]).…”

“…Theoretical studies showed that the configuration of C 70 s inside SWCNT depends primarily on tube diameter and does not significantly depend on tube chirality [21,22]. In order to obtain the optimal structure of the C 70 inside the nanotubes, an energy minimization procedure was performed by Fegani et al (for more detail, see reference [21]). The authors found that the C 70 molecules adopt a lying orientation for small SWCNT diameters (below 1.356 nm), whereas a standing orientation is preferred for large diameters (above 1.463 nm).…”

“…Ref [53] Ref [54] Ref [55] Ref [56] Ref [57] Ref [21] low-and high-frequency component associated to the vibrations along the circumferential direction (G−) and the G direction of the nanotube axis (G+), respectively. In both metallic and semiconducting nanotubes, the former component is found to be dependent on the diameter of a nanotube, while the latter does not exhibit this dependence [40].…”

“…The intermolecular distances of various fullerenes in SWCNTs are considerably smaller than those for bulk fullerene crystals, suggesting an effect of confinement in the one-dimensional channels inside SWCNTs. Raman experiments on SWCNTs encasing C 70 molecules have been reported [19,21,42,47,48]. Ryabenko et al [42] concluded that the PRBLM mode of C 70 peapods are downshifted by ∼2-3 cm…”

“…The evolution of the nonresonant Raman scattering intensity ratios between the Raman mode of fullerene peas and nanotubes as a function of the fullerene concentration inside the tubes has been investigated in the framework of the spectral moment's method [21,50]. Although the nonresonant approach cannot predict the variation of the line intensities with the excitation energies, the obtained predictions are useful to follow their evolution as a function of the filling rate of fullerenes inside SWCNT.…”