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.

Single-Wall Carbon Nanotubes (SWNTs) non-covalently functionalized with organic molecules have proven to be a very promising light-harvesting system. The goal is to combine the unique transport and optical properties of nanotubes with the wide tunability of organic molecules properties. Among those molecules, porphyrins, a precursor of photosynthetic centers, show a strong absorption in the visible that is already used in dye sensitized hybrid solar cells [1]. Porphyrins link to SWNTs through π-stacking interaction which preserves most of the intrinsic properties of the SWNTs, in contrast with covalent functionalization. Moreover, the coupling is still strong enough to induce new functionalities. It was recently shown that efficient excitation energy transfer (EET) can occur in such system [2,3]. The very high quantum yield reported in this system suggests that the EET mechanism must occur on an ultrafast time-scale [4]. In order to characterize the nature of the EET mechanism, we investigate its dynamics at a subpicosecond time scale, by means of pump-probe spectroscopy. We show that the ground state recovery time of porphyrin in the compound is reduced by several orders of magnitude compared to the case or free porphyrin (Fig. 1). Concomitantly, a strong bleaching signal is observed on the optical resonances of the nanotubes showing an ultrafast population build-up upon excitation of the porphyrin (Fig. 2). We conclude that the energy transfer occurs on a time scale shorter than 100fs and that the surrounding of SWNTs by porphyrins does not affect the relaxation dynamics. References [1] W. M. Campbell, et al., The Journal of Physical Chemistry C, 111, 11760 (2007). [2] G. Magadur, et al., ChemPhysChem, 9, 1250 (2008).pp. 200-205. [3] J. P. Casey, et al., Journal of Materials Chemistry, 18, 1510 (2008). [4] C. Roquelet, et al., Applied Physics Letters, 97, 141918 (2010).

Single-Wall Carbon Nanotubes (SWNTs) non-covalently fonctionalized with organic molecules have proven to be a very promising light-harvesting system. The goal is to combine the unique transport properties of nanotubes with the wide tunability of organic molecules properties. Among those molecules, porphyrins, a precursor of photosynthetic centers are already used in dye sensitized hybrid solar cells [1]. Porphyrins link to SWNTs through π-stacking interaction which preserves most of the intrinsic properties of the SWNTs, in contrast with covalent functionalization. Moreover, the coupling is still strong enough to induce an efficient excitation energy transfer (EET) [2,3]. The very high transfer yield reported in this system suggests that the EET mechanism must occur on an ultrafast time-scale [4]. In order to characterize the nature of the EET mechanism, we investigated its dynamics at a subpicosecond time scale, by means of pump-probe spectroscopy. We show that the ground state recovery time of porphyrin in the compound is reduced by several orders of magnitude compared to the case or free porphyrin (Fig. 1). Concomitantly, a strong bleaching signal is observed on the optical resonances of the nanotubes showing an ultrafast population build-up upon excitation of the porphyrin (Fig. 2). We conclude that the energy transfer occurs on a time scale shorter than 100fs and that the surrounding of SWNTs by porphyrins does not affect the relaxation dynamics. Probing excited states of the nanotubes and porphyrin further allows to track the energy transfer path in the supra molecular compound. References [1] W. M. Campbell, et al., The Journal of Physical Chemistry C, 111, 11760 (2007). [2] G. Magadur, et al., ChemPhysChem, 9, 1250 (2008).pp. 200-205. [3] J. P. Casey, et al., Journal of Materials Chemistry, 18, 1510 (2008). [4] C. Roquelet, et al., Applied Physics Letters, 97, 141918 (2010).

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.

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.

We review the main information that we have obtained from combined Raman spectroscopy and electron diffraction experiments on individual free-standing single-walled carbon nanotubes. This information concerns: the radial breathing mode vs. diameter relationship; the dependence of the frequency and lineshape of the G-modes in semiconducting and metallic tubes; the evaluation of the optical transition energies for individual free-standing SWNTs. From these data, we can define Raman criteria allowing the indexing of carbon nanotubes from their Raman features only. We show the efficiency of this approach to assign the (n,m) indices of individual chiral and achiral single-walled carbon nanotubes. These criteria are also applied to identify tubes grown on a substrate from a single wavelength Raman experiments. These results obtained on index-identified individual nanotubes are compared with theoretical predictions. (c) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim