The ultimate surface exposure provided by graphene monolayer makes it the ideal sensor platform but also exposes its intrinsic properties to any nvironmental perturbations. We show in this work that structural and electronic characterization of graphene in air by Raman spectroscopy is significantly affected by the substrate surface cleaning method and moderate laser power conditions. In particular, we demonstrate that the charge carrier density of graphene exfoliated on a SiO2/Si substrate can be finely and reversibly tuned between electron and hole doping with visible photons. The amplitude of this photo-induced doping is found to require hydrophilic substrates and to vanish in suspended graphene. These findings suggest that optically gated graphene devices operating with a sub-second time scale can be envisioned but also that Raman spectroscopy might not be as non-invasive as generally assumed.

The ultimate surface exposure provided by graphene monolayer makes it the ideal sensor platform but also exposes its intrinsic properties to any environmental perturbations. We show in this work that structural and electronic characterization of graphene in air by Raman spectroscopy is significantly affected by the substrate surface cleaning method and moderate laser power conditions. In particular, we demonstrate that the charge carrier density of graphene exfoliated on a SiO2/Si substrate can be finely and reversibly tuned between electron and hole doping with visible photons. The amplitude of this photo-induced doping is found to require hydrophilic substrates and to vanish in suspended graphene. These findings suggest that optically gated graphene devices operating with a sub-second time scale can be envisioned but also that Raman spectroscopy might not be as non-invasive as generally assumed.

Des modifications des températures de transition voire l’apparition de nouvelles phases n’existant pas pour les matériaux macroscopiques peuvent être trouvées. De premiers résultats, dans le cas de nanoparticules et nanofils de fer confinés dans des nanotubes de carbone, ont été obtenus par les équipes du LPS (Orsay), du LFP (Saclay), et du CEMHTI (Orléans) sur la ligne DIFFABS.

The potential impact of industrial multiwalled carbon nanotubes (MWNTs) was investigated under normalized laboratory conditions according to the International Standard micronucleus assay ISO 21427–1 for 12 days of half-static exposure to 0.1, 1, 10 and 50 mg/l of MWNTs in water. Three different end points were carried out for 12 days of exposure: mortality, growth inhibition and micronuclei induction in erythrocytes of the circulating blood of larvae. Raman spectroscopy ana lysis was used to study the presence of carbon nanotubes in the biological samples. Considering the high diversity of carbon nanotubes according to their different characteristics, MWNTs were analyzed in Xenopus larvae, comparatively to double-walled carbon nanotubes used in a previous study in similar conditions. Growth inhibition in larvae exposed to 50 mg/l of MWNTs was evidenced; however, no genetoxicity (micronucleus assay) was noticed, at any concentration. Carbon nanotube localization in the larvae leads to different possible hypothesis of mechanisms explaining toxicity in Xenopus.

Considering the important production of carbon nanotubes (CNTs), it is likely that some of them will contaminate the environment during each step of their life cycle. Nevertheless, there is little known about their potential ecotoxicity. Consequently, the impact of CNTs on the environment must be taken into consideration. This work evaluates the potential impact of well characterized double-walled carbon nanotubes (DWNTs) in the amphibian larvae Xenopus laevis under normalized laboratory conditions according to the International Standard micronucleus assay ISO 21427-1:2006 for 12 days of half-static exposure to 0.1–1–10 and 50 mg L-1 of DWNTs in water. Two different endpoints were carried out: (i) toxicity (mortality and growth of larvae) and (ii) genotoxicity (induction of micronucleated erythrocytes). Moreover, intestine of larvae were analyzed using Raman spectroscopy. The DWNTs synthetized by catalytic chemical vapor deposition (CCVD) were used as produce (experiment I) and the addition of Gum Arabic (GA) was investigated to improve the stability of the aqueous suspensions (experiment II). The results show growth inhibition in larvae exposed to 10 and 50 mg L-1 of DWNTs with or without GA. No genotoxicity was evidenced in erythrocytes of larvae exposed to DWNTs, except to 1 mg L-1 of DWNTs with GA suggesting its potential effect in association with DWNTs at the first nonacutely toxic concentration. The Raman analysis confirmed the presence of DWNTs into the lumen of intestine but not in intestinal tissues and cells, nor in the circulating blood of exposed larvae.

A new approach for the stabilisation of double-walled carbon nanotubes in aqueous media was developed. A low molecular weight surfactant was used in the first stage for the debundling of the nanotubes followed by substitution with a higher molecular weight surfactant or non-ionic surfactants. Dispersions were characterized by optical density measurements, SEM and DLS. The presence of remaining low molecular weight surfactant was investigated by FT-IR. Double walled carbon nanotube dispersions showed good dispersion stability and non-detectable amounts of the initial surfactant, which was completely removed. Such a method could be useful for preparation of stable aqueous dispersions of carbon nanotubes with low concentration of surfactants, which is especially important for toxicity studies.

Carbon nanotubes (CNT) were synthesized from a H2–CH4 mixture with W/Co–MgO catalyst by a catalytic chemical vapour deposition (CCVD) method. Different W/Co ratios were investigated. From transmission electron microscopy observations, we observed that both the number of walls and the diameter of CNT increased with the proportion of tungsten. A promoter effect was observed as long as the proportion of tungsten was kept low and CNT with a number of walls ranging from 2 to 5 were obtained. With a higher proportion of tungsten, multi-walled carbon nanotubes (MWNT) up to 10 walls were synthesised, together with additional undesirable carbon nanofibres.