The temperature dependence of the Raman spectrum of a gelatine-based composite material doped with single-walled carbon nanotubes (SWNT@gelatin) is reported [1]. A significant up-shift of the G-mode frequency is observed when the temperature is decreased from room temperature to 20 K. This frequency shift is significantly stronger than the one found for pure thermal effects. In contrast, the features of the radial breathing modes (frequencies and width) display no significant change in the same temperature range. These results are well understood by considering a uniaxial strain on the nanotube induced by the thermal expansitivity mismatch between the nanotube and the surrounding matrix [2,3]. These conclusions are in good agreement with photoluminescence experiments performed on the same samples [4]. References [1] D. Levshov, J. Phys. Chem. C 2010, 114, 16210-16214. [2] S. Cronin, Phys. Rev. Lett. 2004, 93, 167401. [3] G. Wu, Phys. Rev. B 2005, 72, 115411. [4] S. Berger, J. Appl. Phys. 2009, 105, 094323.

The Hybrid system consisting in quaterthiophene derivative inserted into single and multi-walled carbon nanotubes is studied. Encapsulation efficiency of the conjugated oligomers in the hollow core of nanotube is investigated by Transmission Electron Microscopy and spatial resolved electron energy loss spectroscopy. We clearly show from Raman spectroscopy that the interaction between nanotubes and oligomers deeply depends on the metallic or semiconducting character of nanotubes. The charge transfer is shown to be significantly stronger for semiconducting tubes than for metallic ones. In addition, the shift of the Raman-active G band together and the appearance of a new peak in the 2D band of the semiconducting nanotubes state a ntype doping of the nanotubes. Complementary, the infrared spectra evidence a p-type doping of the oligomer.

The temperature dependence of the Raman spectrum of a gelatine-based composite material doped with single-walled carbon nanotubes (SWNT@gelatin) is reported [1]. A significant up-shift of the G-mode frequency is observed when the temperature is decreased from room temperature to 20 K. This frequency shift is significantly stronger than the one found for pure thermal effects. In contrast, the features of the radial breathing modes (frequencies and width) display no significant change in the same temperature range. These results are well understood by considering a uniaxial strain on the nanotube induced by the thermal expansitivity mismatch between the nanotube and the surrounding matrix [2,3]. These conclusions are in good agreement with photoluminescence experiments performed on the same samples [4]. References [1] D. Levshov, J. Phys. Chem. C 2010, 114, 16210–16214. [2] S. Cronin, Phys. Rev. Lett. 2004, 93, 167401. [3] G. Wu, Phys. Rev. B 2005, 72, 115411. [4] S. Berger, J. Appl. Phys. 2009, 105, 094323.

Le corannulène C20H10 est une molécule en forme de coupelle composée de cycles pentagonaux et hexagonaux appartenant à la famille des polyarènes géodésiques. Les nano-molécules de polyarènes géodésiques peuvent s’organiser dans la formation de cristaux moléculaires. Dans le cas du corannulène, la structure du cristal a été reportée pour la première fois en 1976, [1] comme appartenant à au groupe d’espace monoclinique P21c puis cette structure a été récemment confirmée [2]. Dans cette structure la cellule unité est composée de deux molécules se présentant dans deux orientations différentes de manière inclinée par rapport à l’axe de symétrie de la molécule. Quelques travaux reportent l’étude du corannulène par spectroscopie vibrationnelle, mais la plupart de ces travaux sont bases sur des simulations [3,4]. Les spectroscopies vibrationnelles s’avèrent être des outils très intéressants pour étudier de telles molécules. En effet, de part leur courbure, les polyarènes géodésiques sont très différentes des molécules planes ou des cages rigides : la nature des liaisons est très différente. Par ailleurs, les interactions avec l’environnement peuvent entraîner une distorsion de la molécule et donc une brisure de symétrie donnant ainsi naissance à des modes de vibration auparavant interdits. Dans ce travail, nous nous sommes intéressés à l’influence de la température et de la pression sur les modes de vibration des molécules de corannulène, comment ces modes évoluent-ils ? voit-on apparaître de nouveaux modes? La spectroscopie vibrationnelle est également très sensible à la structure des cristaux moléculaires notamment au travers des modes Raman basses fréquences. Comment cette structure évolue-t-elle avec la température et la pression ? Quelles sont les interactions entre les molécules dans ces cristaux et comment évoluent-elles ? Nous montrerons que les outils spectroscopiques apportent déjà des premières réponses à ces questions.

The high pressure behaviour of polyiodides confined into the hollow core of single walled carbon nanotubes organized into bundles has been studied by means of Raman spectroscopy. Several regimes of the structural properties are observed for the nanotubes and the polyiodides under pressure. Raman responses of both compounds exhibit correlations over the whole pressure range (0-17 GPa). Modifications in particular take place respectively between 1 and 2.3 GPa for polyiodides and between 7 and 9 GPa for nanotubes, depending on the experiment. Differences between one experiment to another are discussed in terms of nanotube filling homogeneity. These transitions can be presumably assigned to the tube ovalization pressure and at the tube collapse pressure. A non reversibility of several polyiodide mode modifications is evidenced and interpreted in terms of a progressive linearization of the iodine polyanions and a reduction of the charged species on pressure release. Furthermore, the significant change of the mode intensities could be associated to an enhancement of lattice modes, suggesting the formation of a new structure inside the nanotube. Changes of the nanotube mode positions after pressure release features point out a decrease of the charge transfer in the hybrid system consistent with the observed evolution of the charged species.

Hybrid system consisting in quaterthiophene derivative inserted into single and multi-walled carbon nanotubes is studied. Encapsulation efficiency of the conjugated oligomers in the hollow core of nanotube is investigated by Transmission Electron Microscopy and spatial resolved electron energy loss spectroscopy. We clearly show from Raman spectroscopy that the interaction between nanotubes and oligomers deeply depends on the metallic or semiconducting character of nanotubes. The charge transfer is shown to be significantly stronger for semiconducting tubes than for metallic ones. In addition, the shift of the Raman-active G band together with the appearance of a new peak in the 2D band of the semiconducting nanotubes state a n-type doping of the nanotubes. Complementary, the infrared spectra evidence a p-type doping of the oligomer.

The high-pressure behavior of polyiodides confined into the hollow core of single-walled carbon nanotubes organized into bundles has been studied by means of Raman spectroscopy. Several regimes of the structural properties are observed for the nanotubes and the polyiodides under pressure. Raman responses of both compounds exhibit correlations over the whole pressure range (0–17 GPa). Modifications, in particular, take place, respectively, between 1 and 2.3 GPa for polyiodides and between 7 and 9 GPa for nanotubes, depending on the experiment. Differences between one experiment to another are discussed in terms of nanotube filling homogeneity. These transitions can be presumably assigned to the tube ovalization pressure and to the tube collapse pressure. A nonreversibility of several polyiodide mode modifications is evidenced and interpreted in terms of a progressive linearization of the iodine polyanions and a reduction in the charged species on pressure release. Furthermore, the significant change in the mode intensities could be associated to an enhancement of lattice modes, suggesting the formation of a new structure inside the nanotube. Changes in the nanotube mode positions after pressure release point out a decrease in the charge transfer in the hybrid system consistent with the observed evolution of the charged species.