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.

Over the past two decades significant efforts have been directed towards the elucidation of synthesis/structure/function correlations to guide the development of synthetic strategies for controlling the composition, size and shape of nanomaterials. In this context, organic–inorganic nanohybrids incorporating bridged silsesquioxanes have been of particular interest, due to their versatility and the structural control that can be achieved through independent modulation of the properties of the organic bridge and inorganic moieties. Such strategies have also been applied to the production of thin films on a variety of substrates, driven by the continuous need to develop new and enhanced materials with nanostructures engineered over multiple length scales for applications in electronics, optics, sensing, ferromagnetic, shape-selective membranes, etc. In this talk, I will first present a fundamental study of the nanostructuring mechanisms of model hybrid silica. Our experimental investigation was performed using an in operando approach (vibrational spectroscopies under pressure, light diffusion, microscopy) coupled with DFT calculations. Parameters controlling the evolution of the system during sol−gel processing: supramolecular interactions, hydrolysis, polycondensation, and nucleation and growth of the hybrid solid in solution were investigated. The relation between structural properties and applications will be then highlighted1-4.

Chalcogenide glasses exhibit remarkable properties, which could be used in the development of electrical memory susceptible to replace the current flash memories. During the last decades, a strong interest has been focused on superionic Ag-Ge-Se glasses for their high ionic conductivity, a property that could be used to develop ionic Conductive-Bridging Random Access Memories (CB-RAM). Bulk Ag-Ge-Se glasses have already been widely studied for their electrical, structural and thermal properties. In particular it was shown that the conductivity of phase separated Agx(Ge0.25Se0.75)100-x glasses increases suddenly by seven to eight orders of magnitude at 7-10 at.%Ag. The percolation of the Ag-rich phase was at the origin of this sudden jump in conductivity. Despite a convergence on the inhomogeneous nature of these glasses, some questions remain open such as the composition of the Ag-rich and Ag-poor phases, size and shape of the different phases. These questions has hardly been treated in literature to date. In this talk, investigations on bulk Agx(Ge0.25Se0.75)100-x glasses will be performed focusing on the inhomogeneous nature of the glasses. Macroscopic and local studies of vibrational and mechanical properties will conduct using Raman (mapping) spectroscopy, Vickers microhardness and Contact Resonance Atomic Force Microscopy (CR-AFM). For the glass containing 10 at. % in Ag, Raman mapping will give evidence of a phase separation for through continuous interpenetrating phases in the spinodal decomposition process. Combined mechanical characterizations will indicate that the microhardness and rigidity modulus decrease with the silver content in the glass. At nanoscale level, CR-AFM measurements will highlight a modulation of the rigidity with Ag content. The structural origin of these changes will be confirmed using Raman mapping evidencing modifications in the tetrahedral network between two phases. The results could suggest a different Ge/Se ratio in Ag-poor and Ag-rich phases.

Middle infrared response on a carbon nanotube is very weak because this homonuclear allotrope of carbon does not bear permanent dipoles. Nevertheless, a significant number of infrared phonons are predicted by the group theory. Encapsulating molecules inside nanotubes (called hybrid nanotubes in the following) is a common strategy to add new functionalities. The one-dimensional nature of single-walled carbon nanotubes (SWCNT) internal channels has been exploited here to induce a molecular order and specific interactions which are dependent of the size of the nano container (figure).Here we report the discovery of a strong dependence on the infrared response of the hybrid nanotube due to confinement effect when dimethylquaterthiophenes are encapsulated inside SWCNTs1. Results are compared to experiments performed on nanotubes where dyes are π-stacked at the outer surface. Surprisingly, the confinement properties lead to an exaltation of the infrared absorption response in the carbon nanotubes from dye molecule interactions. Thanks to the comparison between the experimental investigations and DFT calculations, we elucidate the origin of the large enhancement of this infrared absorption and demonstrate that interactions between conjugated oligomers and nanotubes can be probed.

Results and questions aboutStructural properties of molecules inside carbon nanotubes

Le contrôle de la structure et de la morphologie de solides hybrides organiques-inorganiques est un élément clef pour la conception de matériaux fonctionnels. En particulier, pour les silsexquioxanes pontants (SP) auxquels nous nous intéressons, il a été montré que structure et morphologie pouvaient être contrôlées à travers la maitrise des conditions de synthèses (PH, Solvant, …) : à partir d’une même molécule précurseur, des matériaux lamellaires, amorphes, tubulaires, ou de morphologies spongieuses ont pu être obtenus. Les SP présentent l’avantage d’être fonctionnalisés soit en incluant des groupes fonctionnels au sein des molécules précurseurs, soit par l’association de ces précurseurs à des ions/molécules fonctionnelles au cours de la synthèse. A travers un travail centré sur les spectroscopies vibrationnelles, nous nous intéressons aux mécanismes de structurations de ces matériaux, afin d’optimiser leur contrôle et leur impact sur les propriétés de ces matériaux fonctionnels. Ces mécanismes intervenant au cours la réaction sol-gel sont fortement impactés par la compétition entre l’auto-assemblage par liaisons non covalentes (formation de ponts intermoléculaires par liaisons hydrogènes entre amides) et la condensation de la sous structure inorganiques (formation de liaisons covalentes Si-O-Si). Les conditions de synthèse jouent un rôle important dans la maîtrise de cette compétition, nous montrons également qu’il est également possible de jouer sur les liaisons hydrogène en jouant sur la substitution amide/thioamide (conformation/force de liaisons…). La maitrise de la structure et de la substitution amide/thioamide jouent un rôle sur les propriétés d’absorption de la lumière des SP. Ces matériaux, si on maitrise gamme et efficacité d’absorption de la lumière présentent un potentiel pour l’incorporation d’ions luminescents lanthanides, favorisant un effet d’antenne par les sous structures du SP jouant le rôle de ligands pour les ions Ln3+. A travers les spectroscopies vibrationnelles nous montrons un fort impact du choix des précurseurs jouant le rôle de ligands, et de la présence de ces ligands sur les propriétés d’assemblages des précurseurs. La compréhension de ces mécanismes a permis d’élaborer des films de rendements quantiques absolus de l’ordre de 0.60±0.02 (excitation 345 nm) permettant l’élaboration de concentrateurs solaires de rendement de conversion de l’ordre de 12.3% lorsqu’ils sont excités dans la gamme (300-380nm).Dans un deuxième temps, nous nous intéressons au comportement de ces matériaux SP sous haute pression et nous montrons que les liaisons hydrogènes confèrent à ces matériaux une élasticité, jouant le rôle de nano-ressorts. A travers une étude in-situ en IR, nous étudions l’impact de la structuration et de la modulation de la liaison hydrogène sur la limite de ce domaine élastique.