Des solutions colloïdales sont assez facilement obtenues à partir de nanoparticules de carbone (nanotubes ou dérivés du graphène) dispersées dans l’eau [1]. L’obtention de mésophases nécessite cependant un soin expérimental dans le tri des nanoparticules et dans la qualité des dispersions. La persistance de fortes interactions attractives et d’agrégats dans une solution peuvent en effet déstabiliser lentement ces phases ou au mieux modifier fortement leurs propriétés visco-élastiques. Depuis plusieurs années, nous étudions comment obtenir à partir de ces solutions, des films et couches minces de propriétés variables en contrôlant les conditions de préparation et de dépôts (orientation des particules, texturation).
Dans ce travail, nous décrirons comment créer et stabiliser des textures périodiques de grande échelle dans des phases nématiques d’oxyde de graphène (voir fig.1). Ces textures ont été caractérisées en microscopie optique et électronique et nous discuterons de leur origine et de leur stabilité.
Références:
[1] C. Zakri, et al. Phil. Trans. R. Soc. A., , 2013, 371, 20120499.

In situ and ex situ Raman measurements were used to study the dynamics of the populations of single-walled carbon nanotubes (SWCNTs) during their catalytic growth by chemical vapor deposition. Our study reveals that the nanotube diameter distribution strongly evolves during SWCNT growth but in dissimilar ways depending on the growth conditions. We notably show that high selectivity can be obtained using short or moderate growth times. High-resolution transmission electron microscopy observations support that Ostwald ripening is the key process driving these seemingly contradictory results by regulating the size distribution and lifetime of the active catalyst particles. Ostwald ripening appears as the main termination mechanism for the smallest diameter tubes, whereas carbon poisoning dominates for the largest ones. By unveiling the key concept of dynamic competition between nanotube growth and catalyst ripening, we show that time can be used as an active parameter to control the growth selectivity of carbon nanotubes and other 1D systems.

We show that the properties of thin conductive inkjet printed lines of single-walled carbon nanotubes (SWCNT) can be greatly tuned, using only a few deposition parameters. The morphology, anisotropy and electrical resistivity of single-stroke printed lines are studied as a function of ink concentration and drop density. An original method based on coupled profilometry-Raman measurements is developed to determine the height, mass, orientational order and density profiles of SWCNT across the printed lines with a micrometric lateral resolution. Height profiles can be tuned from 'rail tracks' (twin parallel lines) to layers of homogeneous thickness by controlling nanotube concentration and drop density. In all samples, the nanotubes are strongly oriented parallel to the line axis at the edges of the lines, and the orientational order decreases continuously towards the center of the lines. The resistivity of 'rail tracks' is significantly larger than that of homogeneous deposits, likely because of large amounts of electrical dead-ends.

We have recently described how metastable aqueous dispersions of single layer graphene (SLG) can beprepared simply by transferring SLG, prepared by oxidation of fully exfoliated graphenide, into water, with nosurfactant.1 The aqueous graphene dispersions are named eau de Graphene (EdG) to convey the idea of waterwith only graphene inside.Here, we report the intrinsic Raman signatures of graphene dispersed in EdG and we show that theycorrespond to all the expected characteristics of SLG. We stress the difference in these signatures with respect tothose of the natural graphite precursor and to those of some aqueous dispersions of few-layers graphene (FLG)stabilized by surfactants. We discuss the Raman shifts of the G and 2D band in terms of doping and strain of thegraphene flakes2,3. Finally, by comparing the second order Raman signatures (D and D’ bands)3 of EdG and thoseof corresponding thin films, we discuss the nature and amount of defects on the graphene sheets.4,5 All togetherthis provides a full description of the structure and properties of graphene flakes dispersed in water without anyadditive.

Les nanotubes de carbone monofeuillets (SWNT) présentent des propriétés physiques originales dues à leur composition –ils sont constitués uniquement d’atomes de carbone– et à leur faible dimensionnalité. En ce qui concerne leurs propriétés optiques, les SWNT semi-conducteurs émettent de la lumière dans le proche infrarouge –on parle de photoluminescence ou de fluorescence– à des longueurs d’onde qui dépendent de leur structure et de leur environnement diélectrique. Cet article traitera des phénomènes physiques à l’origine de la photoluminescence des SWNT, et en particulier leurs propriétés excitoniques, l’influence de la structure et de l’environnement sur le spectre de photoluminescence, ainsi que les perspectives d’applications en photonique.

We synthesized KC8 by simply mixing molten potassium and graphite at 180 °C under inert atmosphere. The KC8 showstypical shiny bronze color, Raman characteristics and XRD pattern of an efficiently intercalated stage 1 GIC, and is ofsufficient quality to produce fully exfoliated graphenide solutions in tetrahydrofuran (THF) and subsequently single layer graphene in water as “eau de graphene” (EdG). The evolution of absorption and Raman spectroscopic signatures of the EdGas a function of processing conditions give key indications on the number of layers of the graphene flakes dispersed in EdG.

We report a detailed Raman study of single layergraphene dispersed in degassed water without additives (SLGiw), so-called “‘eau de graphene”’ (EdG).23 The most characteristic signature of SLGiw is a narrow (28 ± 2 cm−1) and symmetric 2D band. The intensity of the D band is dominated by the contribution of sp3 defects due to slight functionalization of the basal-planes. The density of defects is estimated in the range 200-650 ppm by studying thin films prepared from EdG. These defects can be fully and easily cured by annealing the films at 800 °C. The position of the G and 2D bands, blue-shifted with respect to pristine SLG, are assigned to moderate biaxial compressive strain (≈0.09 ± 0.02%) and likely weak n doping (<4 × 1012 electrons/cm2) of SLGiw.