We examine the excitonic nature of the E33 optical transition of the individual free-standing index-identified(23,7) single-walled carbon nanotube by means of the measurements of its radial-breathing-mode and G-modeRaman excitation profiles. We confirm that it is impossible to determine unambiguously the nature of its E33optical transition (excitonic vs band to band) based only on the excitation profiles. Nevertheless, by combiningRaman scattering, Rayleigh scattering, and optical absorption measurements on strictly the same individual(23,7) single-walled carbon nanotube, we show that the absorption, Rayleigh spectra, and Raman excitationprofiles of the longitudinal and transverse G modes are best fitted by considering the nature of the E33 transitionas excitonic. The fit of the three sets of data gives close values of the transition energy E33 and damping parameter. This comparison shows that the fit of the Raman excitation profiles provides with good accuracy the energy and damping parameter of the excitonic optical transitions in single-walled carbon nanotubes.

Ce travail, qui concerne l’étude des nanotubes de carbone mono- et double parois, comporte deux volets distincts: (i) une compréhension des propriétés optiques et phononiques intrinsèques des nanotubes de carbone individuels, (ii) une approche expérimentale originale des propriétés des nanotubes de carbone double-parois fonctionnalisés de manières covalente et non-covalente. Concernant l’étude des propriétés intrinsèques des nanotubes de carbone individuels, des informations originales ont été obtenues en couplant des résultats de spectroscopie Raman, incluant la mesure des profils d’excitation des différents modes, avec des données d’absorption optique et de diffraction électronique. De manière générale, l’approche que nous avons développée a mis en avant la complémentarité de la spectroscopie Raman et de la diffraction électronique pour l’identification « la plus probable » de la structure de chaque tube. Parmi les résultats obtenus sur les tubes mono-paroi (SWNTs) individuels, on peut souligner la confirmation originale du caractère excitonique des transitions optiques obtenue en combinant des données d’absorption et de profils d’excitation Raman, ainsi que la mise en évidence d’un comportement inattendu des rapports d’intensité des composantes LO et TO des modes G. L’étude des nanotubes de carbone double-parois (DWNTs) individuels de structures clairement identifiées a permis de comprendre le rôle de la distance inter-tubes dans les déplacements en fréquence des modes Raman (modes de respiration (RBLM) et modes G), en associant à une distance inter-tube donnée une pression interne négative (positive) quand cette distance est supérieure (inférieure) à 0.34 nm. D’autre part, le rôle des effets d’interférences quantiques dans l’évolution avec l’énergie d’excitation des intensités des composantes LO et TO des modes G a été clairement identifié. Enfin, une attribution de l’origine des transitions optiques, mesurées par spectroscopie d’absorption, de différents DWNTs a été proposée.L’étude des propriétés de DWNTs fonctionnalisés a été réalisée en couplant des expériences de spectroscopie Raman, d’absorption UV-visible-NIR et de photoluminescence (PL), incluant les cartes d’excitation de la photoluminescence (PLE), sur des suspensions de DWNTs avant et après fonctionnalisation, (i) covalente via un groupement diazonium, (ii) covalente et non-covalente ( stacking) par un colorant. Ce travail présente une contribution au débat sur une question essentielle pour l’utilisation des DWNTs dans des dispositifs opto-électroniques, à savoir : « les DWNTs luminescent-ils ? Et si oui, quelle est l’origine de la luminescence ? ». La présence de photoluminescence dans nos échantillons de DWNTs est établie, et l’étude de son évolution avec différents types et degrés de fonctionnalisation démontre qu’elle ne peut provenir que des tubes internes des DWNTs (PL intrinsèque aux DWNTs), ou de SWNTs générés par l’extrusion des tubes internes de DWNTs durant la préparation des suspensions. D’autre part, on peut souligner la mise en évidence d’un transfert d’énergie du colorant vers le tube interne quand le colorant est greffé de manière covalente sur la tube externe.

A double-walled carbon nanotube (DWNT), a coaxial composite of two single walled carbon nanotubes (SWNT), provides a unique model to study interactions between thetwo constituent SWNTs. Combining high resolution transmission electron microscopy (HRTEM), electron diffraction (ED), and resonant Raman scattering (RRS) experiments on the same individual suspended DWNT is the ultimate way to relate unambiguously its atomicstructure, defined by the chiral indices of the coaxial outer/inner SWNTs, and its Raman-active vibration modes. This approach is used to investigate the intertube distance dependence of theG-modes of individual index-identified DWNTs composed of two semiconducting SWNTs.We state the main features of the dependence of the G-mode frequencies on the distance between the inner and outer layers: (i) When the interlayer distance is larger than the nominal van der Waals distance (close to 0.34 nm), a downshift of the inner-layer G-modes with respectto the G-modes in the equivalent SWNTs is measured. (ii) The amplitude of the downshiftdepends on the interlayer distance, or in other words, on the negative pressure felt by the innerlayer in DWNT. (iii) No shift is observed for an intertube distance close to 0.34 nm.

Recently, we determined using spatial modulation spectroscopy, over a broad optical spectralrange, the spectrum and amplitude of the absorption cross-section of individual semiconductingsingle-wall carbon nanotubes.[1] Here, we will present resonant Raman excitation profiles (REP)of radial breathing modes and G modes measured on the same SWNTs. The transition energiesand full width at half-maximum (FWHM) obtained using both measurements techniques will becompared to discuss the different models commonly used to fit REP [2] as illustrated on Figure1. Furthermore, interference effects on Raman intensity [3] will also be evidenced in the case oftwo energetically close optical transitions. Finally, some recent results obtained on other systems(SWNTs homogeneous dimer and double-walled carbon nanotubes) will be briefly reported.[1] J.-C. Blancon et al., Nat. Comm. 4 (2013), 2542.[2] C. Thomsen and S. Reich, M. Cardona, R. Merlin (Eds.): Light Scattering in Solid IX,Topics Appl. 3.Physics 108 (2007), pp. 116-232.[3] V. N. Popov and Ph. Lambin, Phys. Rev. B 73 (2006), 165425.

Recently, we determined using spatial modulation spectroscopy, over a broad optical spectral range, the spectrum and amplitude of the absorption cross-section of individual semiconducting single-wall carbon nanotubes. Here, we will present resonant Raman excitation profiles (REP) of radial breathing modes and G modes measured on the same SWNTs. The transition energies and full width at half-maximum (FWHM) obtained using both measurements techniques will be compared to discuss the different models commonly used to fit REP as illustrated on Figure 1. Furthermore, interference effects on Raman intensity will also be evidenced in the case of two energetically close optical transitions. Finally, some recent results obtained on other systems (SWNTs homogeneous dimer and double-walled carbon nanotubes) will be briefly reported.

The optical properties of single-wall carbon nanotubes are very promising for developing novel opto-electronic components and sensors with applications in many fields. Despite numerous studies performed using photoluminescence or Raman and Rayleigh scattering, knowledge of their optical response is still partial. Here we determine using spatial modulation spectroscopy, over a broad optical spectral range, the spectrum and amplitude of the absorption cross-section of individual semiconducting single-wall carbon nanotubes. These quantitative measurements permit determination of the oscillator strength of the different excitonic resonances and their dependencies on the excitonic transition and type of semiconducting nanotube. A non-resonant background is also identified and its cross-section comparable to the ideal graphene optical absorbance. Furthermore, investigation of the same single-wall nanotube either free standing or lying on a substrate shows large broadening of the excitonic resonances with increase of oscillator strength, as well as stark weakening of polarization-dependent antenna effects, due to nanotube-substrate interaction.

Double-wall carbon nanotubes (DWNTs) appear as prototypal nanomaterial for studying coupling interactions [1-4] and screening effects at the nanoscale [5]. In this context, we prepared suspensions of individualized DWNTs in sodium deoxycholate (DOC) from pristine DWNTs (p-DWNTs) and covalently functionalized DWNTs (f-DWNTs). F-DWNTs are prepared by the diazonium route which has been shown to selectively functionalize outer-walls [6, 7]. The samples were studied by UV-Vis-NIR absorption, Raman spectroscopy, and photoluminescence (PL). The optical absorption of DWNTs suspensions in surfactant have been measured up to 2500 nm in order to confirm that the DWNTs are individualized and the covalent functionalization of outer-walls. Raman spectra were measured with several excitation wavelengths between 532 nm and 800 nm. According to [8, 9], we identified the (n,m) of small diameter inner-walls by using radial-breathing-like modes (RBLM) frequencies. Compared with the RBM of individualized HiPCO single-wall nanotubes (SWNTs) samples prepared using the same protocol, we observed a slight upshift of RBLM of inner-walls [1-3]. We measured PL maps with excitation wavelengths in the range 700-950 nm and compared them with results from the literature [11, 12] as well as data obtained on HiPCO SWNTs suspension. The results obtained suggest that inner-walls are luminescent. In order to confirm this conclusion, preliminary results of combined PL/Raman experiments performed at the individual DWNT level will be presented.