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Domaines de Recherche: - Physique/Matière Condensée/Science des matériaux
- Physique/Matière Condensée/Systèmes mésoscopiques et effet Hall quantique
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Dernieres productions scientifiques :
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Physical study individualized Double-wall Carbon Nanotubes by Optical techniques
Auteur(s): TRAN H.-N., SAUVAJOL J.-L., PAILLET M., ZAHAB A. A.
(Affiches/Poster)
GDR-I GNT 2013 (Lorient, FR), 2013-04-09
Résumé: 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.
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Reversible Optical Doping of graphene 
Auteur(s): TIBERJ A. , Rubio-roy Miguel, PAILLET M., HUNTZINGER J.-R., LANDOIS P., Mikolasek Mirko, CONTRERAS S., SAUVAJOL J.-L., Dujardin Erik, ZAHAB A. A.
Conférence invité: GDR-I GNT 2013 (Guidel-Plages, Lorient, FR, 2013-04-08)
Ref HAL: hal-00813854_v1
Résumé: 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.
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Comparative Raman study of individual Double-Walled Carbon Nanotubes and Single-Walled Carbon Nanotubes
Auteur(s): LEVSHOV D., MICHEL T., Than T., PAILLET M., Arenal Raul, JOURDAIN V., Yuzyuk Y., SAUVAJOL J.-L.
Conference: Third International Workshop on Nanocarbon Photonics and Optoelectronics (, FI, 2012-07-29)
Actes de conférence: J. Nanoelectron. Optoelectron., vol. 8 p.9-15 (2013)
Résumé: In this paper, we compare the Raman responses obtained on individual suspended Single-Walled Carbon Nanotubes (SWNTs) and Double-Walled Carbon Nanotubes (DWNTs). We focus on the comparison of the frequencies, line widths, intensities and resonance conditions of the main Raman active modes measured on an index-identified DWNT with those measured on SWNTs having atomic structures close to the inner and outer tubes of the DWNT. By this way, we state that the relation between the radial breathing mode frequencies and the diameters established for SWNTs do not work in DWNTs. We found that resonance of only one tube can be sufficient to observe the response of the coupled layers in DWNTs. These results are understood in terms of mechanical coupling between the layers in DWNTs. We evidence that the spectral line widths of the Raman active modes are systematically narrower for DWNTs compared to the corresponding SWNTs. Finally, we present the measurements of the G modes of two different DWNTs which behave in a different way. For the first one, the frequencies of the G modes are not significantly affected by the interaction between the layers, while for the second one we evidence a downward shift of the LO and TO bands arising from the inner layer.
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In Situ Raman Probing of Graphene over a Broad Doping Range upon Rubidium Vapor Exposure
Auteur(s): PARRET R., PAILLET M., HUNTZINGER J.-R., NAKABAYASHI D., MICHEL T., TIBERJ A., SAUVAJOL J.-L., ZAHAB A. A.
(Article) Publié:
ACS Nano, vol. 7 p.165 (2013)
Ref HAL: hal-00785831_v1
DOI: 10.1021/nn3048878
Résumé: We report in situ Raman scattering experiments on single-layer graphene (SLG) and Bernal bilayer graphene (BLG) during exposure to rubidium vapor. The G- and 2D-band evolutions with doping time are presented and analyzed. On SLG, the extended doping range scanned (up to about 1014 electrons/cm2) allows the observation of three regimes in the evolution of the G-band frequency: a continuous upshift followed by a plateau and a downshift. Overall the measured evolution is interpreted as the signature of the competition between dynamic and adiabatic effects upon n-doping. Comparison of the obtained results with theoretical predictions indicates however that a substrate pinning effect occurs and inhibits charge-induced lattice expansion of SLG. At low doping, a direct link between electrostatic gating and Rb doping results is presented. For BLG, the added electrons are shown to be first confined in the top layer, but the system evolves with time toward a more symmetric repartition of the added electrons in both layers. The results obtained on BLG also confirm that the slope of the phonon dispersion close to the K point tends to be slightly reduced at low doping but suggest the occurrence of an unexpected increase of the phonon dispersion slope at higher electron concentration.
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