Membranes organiques bidimensionnelles

International audienc

Highly ordered Langmuir-Blodgett films based on semi-amphiphilic phthalocyanines

International audienceSemi-amphiphilic phthalocyanines can be built via ion exchange at a fatty acid monolayer-water solution interface and be transferred onto solid substrates to give well-ordered Langmuir-Blodgett film

On the chemical grafting of titanium nitride by diazonium chemistry †

International audienceCurrent research directions with the aim of extending the applications of titanium nitride (TiN) in areas of microelectronics, electrocatalysis, biosensors etc. require identifying new and efficient methods to modify this durable material with desired organic functionalities. We have clearly demonstrated in this work that diazonium chemistry can be considered for surface modification of titanium nitride. Indeed, a near-monolayer of aminophenylene has been reported to be spontaneously grafted onto the TiN surface by simple immersion of the substrates into an acidic solution of the corresponding diazonium cations. X-ray photoelectron spectroscopy measurements strongly suggested a covalent coating of aminophenyl groups on titanium nitride. Surface functionalization with aminophenylene layers was also investigated in presence of hypophosphorous acid and iron powder. Effect of these homogeneous and heterogeneous reducing agents with respect to the formation of aryl layers at different thicknesses was discussed in detail on the basis of conventional hemolytic dediazoniation mechanism in combination with the XPS results

Investigation of nanoelectrodes by Transmission Electron Microscopy

International audienceElectrodes for making connections to single molecules and clusters must have separations smaller than 10 nm. They are therefore difficult or impossible to image with atomic force microscopes (AFM) or Scanning Electron Microscopes (SEM). We have fabricated nanoelelectrodes by different methods to contacts nanoclusters and conjugated molecules and investigated their properties in transmission electron microscope (TEM) and their electrical characteristics at room temperature and at 4.2K. The electrodes are made on SiN4 membranes, which is transparent to high energy electrons and which make it possible to image features of a few nanometers in TEM

In situ generation of indium catalysts to grow crystalline silicon nanowires at low temperature on ITO

International audienceIn situ generation of indium catalyst droplets and subsequent growth of crystalline silicon nanowires on ITO by plasma-enhanced CVD are reported, and the wurtzite (Si-IV) phase is clearly evidenced in some wire

Picosecond Generation of Transient Charge Carriers in Langmuir-Blodgett Films of Semi-Amphiphilic Heterodimers

International audienceLangmuir-Blodgett homolayers are formed by deposition of semi-amphiphilic porphyrin-phthalocyanine heterodimers. The optical and photophysical properties of these dimers have been investigated and compared to the liquid-phase data. Excitation of the dimer results in an instantaneous formation of the singlet excited states, followed by a very efficient charge-transfer reaction. The oxidized porphyrin and reduced phthalocyanine moieties are formed within 2 ps and disappear in 70 ps. The triplet excited states of the porphyrin issued from the intersystem crossing decay pathway of the singlet excited states are formed with a very low quantum yield. They also undergo a charge-transfer reaction, leading to the formation of long-lived transient charge carriers. The photoprocesses determined in the Langmuir-Blodgett films of semi-amphiphilic porphyrin-phthalocyanine heterodimers are almost identical to those previously observed for the same dimers in the liquid phase

Hybrid solar cells based on thin-film silicon and P3HT

International audienceHybrid concepts based on a nanoscale combination of organic and inorganic semiconductors are a promising way to enhance the cost efficiency of solar cells through a better use of the solar spectrum, a higher aspect ratio of the interface, and the good processability of polymers. A new type of solar cells has been investigated. It is based on a heterojunction between regio-regular poly(3-hexylthiophene) as an organic electron donor and silicon as an inorganic electron acceptor. In a first step towards nanostructured devices, cells made of flat thin films of these materials have been studied as a model case of the heterojunction. The materials were characterized through ellipsometry and absorption spectroscopy. The devices were studied by means of their spectral response and their I-V characteristics. By combining these results, the contribution of each layer and the mechanisms of photocurrent generation are explained. The best cells to-date show a power conversion efficiency of 1.6% under AM 1.5 illumination, with a Voc of 0.704 V and a Jsc of 4.22 mA/cm2

Covalent grafting onto self-adhesive surfaces based on aryldiazonium salt seed layers

International audienceThe chemistry of aryldiazonium salts has been thoroughly used in recent years to graft in a very simple and robust way ultrathin polyphenylene-like films on a broad range of surfaces. We show here that the same chemistry can be used to obtain self-adhesive surfaces. This target was reached in a simple way by coating various surfaces with chemisorbed organic films containing active aryldiazonium salts. These self-adhesive surfaces are then put into contact with various species (molecules, polymers, nanoparticles, nanotubes, graphene flakes, etc.) that react either spontaneously or under activation with the immobilized aryldiazonium salts. Our self-adhesive surfaces were synthesized following a simple aqueous two-step protocol based on p-phenylenediamine diazotisation. The first diazotisation step results in the robust grafting of thin polyaminophenylene (PAP) layers onto the surface. The second diazotisation step changed the grafted PAP film into a poly-aryldiazonium polymer (PDP) film. The covalent grafting between those self-adhesive surfaces and the target species was achieved by direct contact or by immersion of the self-adhesive surfaces in solution. We present in this preliminary work the grafting of multi-wall carbon nanotubes (MWCNTs), flakes of highly oriented pyrolytic graphite (HOPG), various organic compounds and copper nanoparticles. We also tested these immobilized aryldiazonium salts as electropolymerization initiators for the grafting-to process

Photoactivated surface grafting from PVDF surfaces

International audienceEconomic and easy methods to tune surface properties of polymers as Poly(vinylidene fluoride) (PVDF) without altering bulk properties are of major interest for different applications as biotechnological devices, medical implant device. . . UV irradiation appears as one of the simplest, easy and safe method to modify surface properties. In the case of self-initiated grafting, it is generally assumed that the pretreatment of the PVDF surface with UV irradiation can yield alkyl and per-oxy radicals originating from breaking bonds and capable of initiating the subsequent surface grafting polymerizations. Surprisingly, the present work shows that it is possible to obtain polymer grafting using low energetic UV-A irradiation (3.1-3.9 eV) without breaking PVDF bonds. An EPR study has been performed in order to investigate the nature of involved species. The ability of the activated PVDF surface to graft different kinds of hydrophilic monomers using the initiated surface polymerization method has been tested and discussed on the basis of ATR FT-IR, XPS and NMR HRMAS results

Charge Transfer Evidence between Carbon Nanotubes and Encapsulated Conjugated Oligomers

International audienceA hybrid system consisting of quaterthiophene derivative inserted into carbon nanotubes is studied. Encapsulation efficiency of the conjugated oligomers in the hollow core of nanotubes is investigated by transmission electron microscopy and spatial-resolved electron energy loss spectroscopy. Infrared spectroscopy showed evidence of a significant positive charge transfer on the inserted oligothiophene. Raman spectra display different behaviors depending on the excitation energy and correlated to the quaterthiophene optical absorption energy. At high excitation wavelength (far from the oligomer resonance), radial breathing modes exhibit a significant upshift consistent with an encapsulation effect. At low excitation wavelength (close to the oligomer resonance), both the G-band shift and the low-frequency modes vanishing suggest a significant charge transfer between the quaterthiophene and the nanotube