Thermopower measurements on pentacene transistors

We present the first thermoelectric measurements on pentacene field effect transistors. We report high values of the Seebeck coefficient at room temperature between 240 and 500 micro V/K depending on the dielectric surface treatment. These values are independent of the thickness of the channel and of the applied gate voltage. Two contributions to the Seebeck coefficient are clearly identified: the expected contribution that is dependent on the position of the transport level and reflects the activated character of carrier generation, and an unexpected intrinsic contribution of 265 plus minus 40 micro V/K that is independent of the temperature and the treatment of the oxide surface. This value corresponds to an unusually large lattice vibrational entropy of 3 kB per carrier. We demonstrate that this intrinsic vibrational entropy arises from lattice hardening induced by the presence of the charge-carrier. Our results provide direct evidence of the importance of electronic polarization effects on charge transport in organic molecular semiconductors.Comment: 7 pages, 8 figures, LaTe

Mesoporous Silica Functionalized by Cyclam-Metal Groups: Spectroscopic Studies and Numerical Modeling

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Current methods to monitor microalgae-nanoparticle interaction and associated effects

International audienceWidespread use of nanoparticles for different applications has diffused their presence in the environment, particularly in water. Many studies have been conducted to evaluate their effects on aquatic organisms. Microalgae are at the base of aquatic trophic chains. These organisms which can be benthic or pelagic, meaning that they can enter into interaction with all kinds of particulate materials whatever their density, and constitute an interesting model study. The purpose of this review was to gather more than sixty studies on microalgae exposure to the different nanoparticles that may be present in the aquatic environment. After a brief description of each type of nanoparticle (metals, silica and plastic) commonly used in ecotoxicological studies, techniques to monitor their properties are presented. Then, different effects on microalgae resulting from interaction with nanoparticles are described as well as the parameters and techniques for monitoring them. The impacts described in the literature are primarily shading, ions release, oxidative stress, adsorption, absorption and disruption of microalgae barriers. Several parameters are proposed to monitor effects such as growth, photosynthesis, membrane integrity, biochemical composition variations and gene expression changes. Finally, in the literature, while different impacts of nanoparticles on microalgae have been described, there is no consensus on evidence of nanomaterial toxicity with regard to microalgae. A parallel comparison of different nanoparticle types appears essential in order to prioritize which factors exert the most influence on toxicity in microalgae cultures: size, nature, surface chemistry, concentration or interaction time

Interactions between polystyrene nanoparticles and Chlamydomonas reinhardtii monitored by infrared spectroscopy combined with molecular biology

International audienceFor several decades, use of nanoparticles (NP) on a global scale has been generating new potential sources of organism disruption. Recent studies have shown that NP can cause modifications on the biochemical macromolecular composition of microalgae and raised questions on the toxicity of plastic particles, which are widespread in the aquatic environment. Polystyrene (PS) particles are among the most widely used plastics in the world. In our experimentation, a combined approach of infrared spectroscopy and molecular biology (real-time PCR) has been applied in order to better apprehend the consequences of interactions between Chlamydomonas reinhardtii, freshwater microalgae and PS NP. Two references have been used, nitrogen deprivation -a well-documented stressor-, and gold nanoparticles (Au-NP). As regards biochemical composition, our experiments show a differing microalga response, according to the NP to which they have been exposed. Results with infrared spectroscopy and gene expression methods are consistent and illustrate variation among several carbohydrates (galactose…). Furthermore, PS-NP seem to react in the same direction as nitrogen limitation, thereby supporting the hypothesis that PS-NP can induce response mechanisms to environmental changes in microalgae. This study highlighted the interest of combining infrared spectroscopy and gene expression as means of monitoring microalgae response to nanoplastics

Some fundamental and applicative properties of [polymer/nano-SiC] hybrid nanocomposites

International audienceHybrid nanocomposites which combine polymer as host matrix and nanocrystals as active elements are promising functional materials for electronics, optics or photonics. In these systems, the physical response is governed by the nanocrystal features (size, surface and defect states), the polymer properties and the polymer-nanocrystal interface. This work reviews some selective nanostructured architectures based on active elements such as silicon carbide (SiC) nanocrystals and polymer host matrices. Beyond an overview of some key properties of the nanocrystals, a main part will be devoted to the electro-optical (EO) properties of SiC based hybrid systems where SiC nanocrystals are embedded in polymer matrices of different chemical nature such as poly-(methylmethacrylate) (PMMA), poly-vinylcarbazole (PVK) or polycarbonate. Using this approach, the organic-inorganic interface effects are emphasised with regard to the dielectric or hole transporting behaviour of PMMA and PVK respectively. These effects are illustrated through different EO responses associated with hybrid composites based on PMMA or PVK

Hybrid nanocomposites based on silicon carbide : Electronic and electro-optical investigations

International audienceNanostructured materials based on the wide band gap semiconductor Silicon Carbide (SiC) nanoparticles as isolated objects, embedded in polymer matrixes or functionalized by thin layer (~2 nm) of conducting polymers were realized. The physical properties of several nanocomposites were investigated including electrical, dielectric, optical and electro-optical features. The Electro-optical properties are marked by enhanced Pockels parameters values due to polymer-nanoparticles interfaces effects. On the other hand, hybrid core-shell functionalization of the nanoparticle surfaces are marked by enhanced electrical conductivities of the network associated to good thermo-mechanical behaviour. The physical origin of the electrical conductivity in these nanomaterials is discussed based on the dynamics of polarons in the hybrid nanocomposites

Synthesis and optical behaviuor of mesoporous silica functionalized by organometallic molecules

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