Synthesis of conducting transparent few-layer graphene directly on glass at 450 °C

International audiencePost-growth transfer and high growth temperature are two major hurdles that research has to overcome to get graphene out of research laboratories. Here, using a plasma-enhanced chemical vapour deposition process, we demonstrate the large-area formation of continuous transparent graphene layers at temperatures as low as 450 °C. Our few-layer graphene grows at the interface between a pre-deposited 200 nm Ni catalytic film and an insulating glass substrate. After nickel etching, we are able to measure the optical transmittance of the layers without any transfer. We also measure their sheet resistance directly and after inkjet printing of electrical contacts: sheet resistance is locally as low as 500 Ω sq-1. Finally the samples equipped with printed contacts appear to be efficient humidity sensors

Functional Π-conjugated polymers based on maleimide for photovoltaic applications

A series of new bis-(2-thienyl) maleimide monomers have been synthesized and characterized. The bis-(2thienyl)maleimide unit has been copolymerized with dierent aromatic comonomers. Stille coupling polymerizations under various conditions have been utilized. The copolymers were then characterized by size-exclusion chromatography and their optical and electronic properties were investigated by UV-Vis absorption spectroscopy and cyclic voltammetry. All maleimide based copolymers shared similar LUMO energy levels, which are largely determined by the acceptor moiety, and are close to that of PC61BM to be eective for charge dissociation. These low band gap polymers have been tested for photovoltaic applications and have shown moderate photovoltaic performance. Interesting results were obtained by adding the polymer to the P3HT:PC61BM mixture, as a third component. The ternary blend BHJ solar cells showed power conversion eciencies of 35% exceeding those of the corresponding binary blends

Molecular Arrangement in Self-Assembled Azobenzene-Containing Thiol Monolayers at the Individual Domain Level Studied through Polarized Near-Field Raman Spectroscopy

6-[4-(phenylazo)phenoxy]hexane-1-thiol self-assembled monolayers deposited on a gold surface form domain-like structures possessing a high degree of order with virtually all the molecules being identically oriented with respect to the surface plane. We show that, by using polarized near-field Raman spectroscopy, it is possible to derive the Raman scattering tensor of the ordered layer and consequently, the in-plane molecular orientation at the individual domain level. More generally, this study extends the application domain of the near-field Raman scattering selection rules from crystals to ordered organic structures

Dendritic Cell-Mediated-Immunization with Xenogenic PrP and Adenoviral Vectors Breaks Tolerance and Prolongs Mice Survival against Experimental Scrapie

In prion diseases, PrPc, a widely expressed protein, is transformed into a pathogenic form called PrPSc, which is in itself infectious. Antibodies directed against PrPc have been shown to inhibit PrPc to PrPSc conversion in vitro and protect in vivo from disease. Other effectors with potential to eliminate PrPSc-producing cells are cytotoxic T cells directed against PrP-derived peptides but their ability to protect or to induce deleterious autoimmune reactions is not known. The natural tolerance to PrPc makes difficult to raise efficient adaptive responses. To break tolerance, adenovirus (Ad) encoding human PrP (hPrP) or control Ad were administered to wild-type mice by direct injection or by transfer of Ad-transduced dendritic cells (DCs). Control Ad-transduced DCs from Tg650 mice overexpressing hPrP were also used for immunization. DC-mediated but not direct administration of AdhPrP elicited antibodies that bound to murine native PrPc. Frequencies of PrP-specific IFNγ-secreting T cells were low and in vivo lytic activity only targeted cells strongly expressing hPrP. Immunohistochemical analysis revealed that CD3+ T cell infiltration was similar in the brain of vaccinated and unvaccinated 139A-infected mice suggesting the absence of autoimmune reactions. Early splenic PrPSc replication was strongly inhibited ten weeks post infection and mean survival time prolonged from 209 days in untreated 139A-infected mice to 246 days in mice vaccinated with DCs expressing the hPrP. The efficacy appeared to be associated with antibody but not with cytotoxic cell-mediated PrP-specific responses

Imagerie et spectroscopies en champ proche optique : de la nano-sonde à la caractérisation de matériaux

Evanescent wave uncommon properties allow for the development of scanning near-field opticalmicroscopy (SNOM) and for creating highly sensitive sensors by surface plasmon excitation. This works deals withdevelopments and investigations to produce near-field optical fiber probes for these both applications.After a review of the actual processes, this work reports a new approach for probes manufacturing. Thewet-etching process, to create the tip at the apex of a tapered fiber, has been improved. Next process steps, cleaningand coating, are performed in an original arrangement of plasma device, based on a modified hollow cathodedischarge. The last step of probe fabrication is the tips opening by a micro-spark between the biased tip and anotherplane electrode working as a corona-like discharge in point-to-plane configuration.The home-made SNOM is detailed and the probe sensitivity is discussed with respect to differentparameters, in order to achieve the highest spatial resolution. Imaging capabilities with nano-materials and the firstSNOM-Raman spectra recorded in our laboratory are shown, emphasizing a sub micrometric spectral resolution.The microscale tip sensors based on the plasmon resonance are reported; the probe's manufacturing processis modified for this spectroscopic approach. The miniaturized sensor allows molecule detection in aqueousenvironment. The Raman scattering enhancement trough these micro-sensors demonstrates the important roleplayed by the localized plasmon resonance.Les propriétés singulières des ondes évanescentes ont permis le développement de la microscopie en champproche optique, mais également l'émergence de capteurs moléculaires basée sur l'excitation de plasmons desurface. Ce travail de thèse est consacré au développement de nano-sondes à base de fibres optiques destinées à cesdeux applications.Après un état de l'art des différents procédés de la littérature, ce travail aborde une nouvelle approche pourcréer des nano-sondes optiques. La gravure chimique, pour créer une pointe à l'extrémité d'une fibre conique, estpremièrement optimisée. Les étapes suivantes sont réalisées dans un dispositif plasma original, basé sur unedécharge en régime de cathode creuse cylindrique. Pour finaliser la fabrication des sondes, les pointes métalliséessont ouvertes in situ avec une micro-étincelle obtenue via une décharge couronne en configuration pointe-plan.Notre microscope est ensuite détaillé et une étude paramétrique est menée afin d'optimiser la formation desimages, les capacités de résolution du sont discutées. A titre d'exemple, le microscope est ensuite appliqué à lascience des nano-matériaux, et quelles pistes d'investigation de nano-structures sont explorées, ainsi que lepotentiel de spectroscopie Raman en champ proche.La spectroscopie résonante des plasmons de surface est aussi abordée. Les sondes spécialement modifiéessont ici destinées à la détection moléculaire en milieu aqueux. Les capteurs ainsi élaborés sont testés dans desmicrovolumes de solution, et leur capacité d'exaltation du signal Raman est présentée

Le TERS, ou comment obtenir une signature chimique à l’échelle nanométrique

Le TERS pour tip enhanced raman scattering, est une technique de pointe (dans tous les sens du terme) basée sur l’amplification du signal Raman relative à la résonance de plasmons de surface. Cette technique non-destructive, qui ne nécessite pas de marquage particulier, permet de caractériser un échantillon à l’échelle nanométrique. Le TERS s’impose aujourd’hui pour sonder les propriétés physico-chimiques des nanomatériaux et participer ainsi au développement de nouvelles applications dans le domaine des nanotechnologies

High resolution probing of multi wall carbon nanotubes by Tip Enhanced Raman Spectroscopy in gap-mode

International audienceWe present Tip Enhanced Raman Spectroscopy (TERS) results with side illumination of a scanning tunneling microscope (STM) Au tip on thin multi wall carbon nanotubes deposited on Au(111) with a 75 nm lateral resolution. The spectral features observed in the enhanced near-field regime are discussed considering also the presence of defects in the tube(s) structure and/or trace amounts of amorphous carbon contaminations

Tip enhanced Raman spectroscopy evidence for amorphous carbon contamination on gold surfaces

International audienceWe show that the origin of the spectral fluctuations frequently observed in tip enhanced Raman spectroscopy (TERS) experiments can be mainly related to the presence of surface-contaminating amorphous carbon- based species. We have monitored the spectral fluctuations originating from the sharp metallic tips used as apertureless near field probes, as well as from commonly used noble metal substrates. A correlation between the tip surface roughness and the carbon-based spectral fluctuations has been revealed. An Au-(1 1 1) bare substrate has been mapped with sub-wavelength resolution by TERS, evidencing the localization of the carbon contaminants on the surface steps and grain boundaries

Imagerie et spectroscopies en champ proche optique (de la nano-sonde à la caractérisation des matériaux)

Les propriétés singulières des ondes évanescentes ont permis le développement de la microscopie en champ proche optique, mais également l émergence de capteurs moléculaires basée sur l excitation de plasmons de surface. Ce travail de thèse est consacré au développement de nano-sondes à base de fibres optiques destinées à ces deux applications. Après un état de l art des différents procédés de la littérature, ce travail aborde une nouvelle approche pour créer des nano-sondes optiques. La gravure chimique, pour créer une pointe à l extrémité d une fibre conique, est premièrement optimisée. Les étapes suivantes sont réalisées dans un dispositif plasma original, basé sur une décharge en régime de cathode creuse cylindrique. Pour finaliser la fabrication des sondes, les pointes métallisées sont ouvertes in situ avec une micro-étincelle obtenue via une décharge couronne en configuration pointe-plan. Notre microscope est ensuite détaillé et une étude paramétrique est menée afin d optimiser la formation des images, les capacités de résolution du sont discutées. A titre d exemple, le microscope est ensuite appliqué à la science des nano-matériaux, et quelles pistes d investigation de nano-structures sont explorées, ainsi que le potentiel de spectroscopie Raman en champ proche. La spectroscopie résonante des plasmons de surface est aussi abordée. Les sondes spécialement modifiées sont ici destinées à la détection moléculaire en milieu aqueux. Les capteurs ainsi élaborés sont testés dans des microvolumes de solution, et leur capacité d exaltation du signal Raman est présentéeEvanescent wave uncommon properties allow for the development of scanning near-field optical microscopy (SNOM) and for creating highly sensitive sensors by surface plasmon excitation. This works deals with developments and investigations to produce near-field optical fiber probes for these both applications. After a review of the actual processes, this work reports a new approach for probes manufacturing. The wet-etching process, to create the tip at the apex of a tapered fiber, has been improved. Next process steps, cleaning and coating, are performed in an original arrangement of plasma device, based on a modified hollow cathode discharge. The last step of probe fabrication is the tips opening by a micro-spark between the biased tip and another plane electrode working as a corona-like discharge in point-to-plane configuration. The home-made SNOM is detailed and the probe sensitivity is discussed with respect to different parameters, in order to achieve the highest spatial resolution. Imaging capabilities with nano-materials and the first SNOM-Raman spectra recorded in our laboratory are shown, emphasizing a sub micrometric spectral resolution. The microscale tip sensors based on the plasmon resonance are reported; the probe s manufacturing process is modified for this spectroscopic approach. The miniaturized sensor allows molecule detection in aqueous environment. The Raman scattering enhancement trough these micro-sensors demonstrates the important role played by the localized plasmon resonanceNANTES-BU Sciences (441092104) / SudocSudocFranceF

Microscopie magnétique à spin unique

International audienceLes méthodes expérimentales permettant de détecter la résonance de spin électronique de défauts ponctuels du diamant ouvrent de nouvelles perspectives pour le développement de capteurs quantiques à haute sensibilité. De tels capteurs ont notamment démontré des performances exceptionnelles pour l’imagerie magnétique aux échelles nanométriques, conduisant à une transition accélérée vers des solutions commerciales