• Sciences de l'ingénieur/ photonique
  
• Physique/Physique/Optique
  
• Physique/Matière Condensée/Science des matériaux
  

Dye confinement into carbon nanotube significantly affects the electronic charge density distribution of the final hybrid system. Using the electron-phonon coupling sensitivity of the Raman G-band, we quantify experimentally how charge transfer from thiophene oligomers to single walled carbon nanotube is modulated by the diameter of the nano-container and its metallic or semiconducting character. This charge transfer is shown to restore the electron-phonon coupling into defected metallic nanotubes. For sub-nanometer diameter tube, an electron transfer optically activated is observed when the excitation energy matches the HOMO-LUMO transition of the confined oligothiophene. This electron doping accounts for an important enhancement of the photoluminescence intensity up to a factor of nearly six for optimal confinement configuration. This electron transfer shifts the Fermi level, acting on the photoluminescence efficiency. Therefore, thiophene oligomer encapsulation allows modulating the electronic structure and then the optical properties of the hybrid system.

We study the intrinsic optical spectroscopy (UV-vis-NIR absorption, Raman and photoluminescence) signatures of single wall carbon nanotubes (SWNT) dispersed in degassed water without additives, so called ‘‘eau de nanotubes” (EdN). They are found to be very close to those of SWNT dispersed in aqueous suspensions stabilized with surfactants. Absorption peaks appear to be even slightly better resolved for EdN, suggesting sharper excitonic resonances, which is also supported by the Raman data. On the other hand, the photoluminescence signal is significantly weaker. These signatures suggest that SWNT are dispersed as individuals in degassed water, in a similar way single layer graphene was recently shown to be readily dispersable in degassed water [1-3].References[1]G. Bepete et al, Nat. Chem. 2016, DOI 10.1038/NCHEM2669[2]G. Bepete et al, J. Phys. Chem. C 2016, 120 (49), 28204–28214.[3]G. Bepte et al, Phys. Stat. Solidi 2016, 10 (12), 895-899.

The main hurdle preventing the widespread useof single-walled carbon nanotubes remains the lack ofmethods with which to produce formulations of pristine,unshortened, unfunctionalized, individualized single-walledcarbon nanotubes, thus preserving their extraordinary properties.In particular, sonication leads to shortening, which isdetrimental to percolation properties (electrical, thermal,mechanical, etc.). Using reductive dissolution and transfer intodegassed water, open-ended, water-filled nanotubes can bedispersed as individualized nanotubes in water−dimethylsulfoxide mixtures, avoiding the use of sonication andsurfactant. Closed nanotubes, however, aggregate immediately upon contact with water. Photoluminescence andabsorption spectroscopy both point out a very high degree of individualization while retaining lengths of several microns.The resulting transparent conducting films are 1 order of magnitude more conductive than surfactant-based blanks atequal transmittance.

The rise of efficient extraction techniques triggered a renewal of interest in semiconducting carbon nanotubes (s-SWNT) research. It represents a great interest for optoelectronics, with outstanding properties in field-effect transistor, and s-SWNT ability to efficiently emit light in the near-IR range. In particular, polyfluorene (PFO) wrapped s‑SWNT (s-SWNT@PFO) display strong photoluminescence, and could be coupled with photonic devices such as microring resonators [1,2] to control photoluminescence linewidth and enhance photoluminescence intensity.The main challenge for using s-SWNT@PFO in optoelectronics lies in the difficulty to establish good electrical contact with a PFO embedded carbon nanotube. We propose to investigate these issues by tuning the amount of PFO wrapping around s-SWNT. A low pressure annealing process is used to selectively remove PFO around s‑SWNT without burning nanotubes themselves (Figure). The resulting s-SWNT@PFO networks are then probed by AFM, Raman spectroscopy, absorption, photoluminescence and electrical experiments.

Nanophotonics is an emerging field where researchers look for potential application of carbon nanotubes (SWNT) in the framework of silicon photonics technology, due to SWNT ability to emit, modulate and detect light in the wavelength range of silicon transparency.In this field of nanotube photonics, a first milestone was to couple light emission from SWNT into silicon waveguides [1]. Current researches focus on coupling SWNT with optical cavities, either for enhancing nanotube photoluminescence (PL) or nonlinear optical phenomena at the nanoscale, using microdisk resonators, or photonic crystal cavities. However, these kinds of cavities could not be easily coupled to silicon waveguides, hindering subsequent integration into more complex photonic devices.Building up on our previous work [2], we propose to couple SWNT PL with silicon microring resonators in a fully integrated configuration, with an acess waveguide [3]. PL coupled to microring modes could be collected from the access waveguide, with efficient rejection on non-resonant photons. Emission quality factor up to 8000 were observed. This design allow for collinear excitation of SWNT through the access waveguide, leading to efficient excitation and collection of SWNT PL at different wavelengths. The requirement for out-of-the-plane SWNT excitation is lifted, underlining the pertinence of this approach for realistic carbon nanotube based photonic devices.References1. E. Gaufrès, N. Izard, A. Noury, X. Le Roux, G. Rasigade, A. Beck and L. Vivien, ACS Nano 6, 3813 (2012)2. A. Noury, X. Le Roux, L Vivien and N. Izard, Nanotechnology 25, 215201 (2014)3. A. Noury, X. Le Roux, L. Vivien and N. Izard, Nanotechnology 26, 345201 (2015)