Structuration et Propriétés Electroniques de Matériaux pi-Conjugués Modèles Sondées à l'Echelle Moléculaire par Microscopie en Champ Proche

The expected limits of silicon-based microelectronics in the coming years, have promoted the development of alternative solutions. Among them, organic electronics, using pi-conjugated organic materials as the active part of components, sounds very attractive. Increases observed the past 20 years in the performances of organic devices, find for a great part their origin in a better structure of the active film and the understanding of the relationship between structure and electronic properties in these materials still appears as a keynote for organic electronics.An STM structural study of self-assembled monolayers of either small molecules synthesised at the laboratory or polythiophenes was carried out in a first time to bring out self-assembly mechanisms. For the polymer monolayers, crystalline properties could be considerably improved with annealing of the sample. An organised second layer was observed for the first time on sample with higher coverage. Finally the influence of local inter or intra-chain conformation on polymer electronic properties was investigated by two-dimensional scanning tunnelling spectroscopy. Although the electronic structure of the polymer seems unaffected by intra-chain defect such as folds, an increase of the bandgap was observed above isolated chains of the second layer. This is rather surprising as such chains are generally assumed to be pi-stacked on the first layer, which should cause a partial closure of the bandgap.La perspective d'atteindre prochainement les limites de la microélectronique à base de silicium a encouragé le développement de solutions alternatives. Parmi elles, l'électronique organique, dans laquelle les éléments actifs du composant sont constitués de systèmes organiques pi-conjugués, semble très prometteuse. Les progrès réalisés ces 20 dernières années sur les performances des dispositifs organiques résultent en grande partie de l'amélioration de la structuration de ces matériaux, et la relation entre structure et propriétés électroniques reste à ce jour l'une des problématiques majeures de l'électronique organique.Une caractérisation structurelle par STM de monocouches auto-assemblées réalisées à base de petites molécules synthétisées au laboratoire (B4OTF et B5OTF) ou de polythiophènes, a été entreprise dans un premier temps afin de dégager les mécanismes régissant l'assemblage des molécules. Dans le cas du polymère, une nette amélioration des propriétés cristallines a pu être obtenue par recuit des échantillons et une deuxième couche structurée a pu être observée pour la première fois sur des échantillons plus concentrés. Enfin l'influence de conformations locales inter ou intra-chaîne du polymère sur ses propriétés électronique intrinsèques a été investiguée par spectroscopie tunnel bidimensionnelle. S'il semble que les défauts intra-chaîne tels que les repliements aient peu d'impact sur la structure électronique du matériau, un surprenant accroissement du gap a été observé sur des chaînes isolées de deuxième couche qu'on suppose généralement en configuration de pi-stacking et donc susceptibles d'expérimenter une plus grande délocalisation électronique

Structuration et Propriétés Electroniques de Matériaux pi-Conjugués Modèles Sondées à l'Echelle Moléculaire par Microscopie en Champ Proche

The expected limits of silicon-based microelectronics in the coming years, have promoted the development of alternative solutions. Among them, organic electronics, using pi-conjugated organic materials as the active part of components, sounds very attractive. Increases observed the past 20 years in the performances of organic devices, find for a great part their origin in a better structure of the active film and the understanding of the relationship between structure and electronic properties in these materials still appears as a keynote for organic electronics.An STM structural study of self-assembled monolayers of either small molecules synthesised at the laboratory or polythiophenes was carried out in a first time to bring out self-assembly mechanisms. For the polymer monolayers, crystalline properties could be considerably improved with annealing of the sample. An organised second layer was observed for the first time on sample with higher coverage. Finally the influence of local inter or intra-chain conformation on polymer electronic properties was investigated by two-dimensional scanning tunnelling spectroscopy. Although the electronic structure of the polymer seems unaffected by intra-chain defect such as folds, an increase of the bandgap was observed above isolated chains of the second layer. This is rather surprising as such chains are generally assumed to be pi-stacked on the first layer, which should cause a partial closure of the bandgap.La perspective d'atteindre prochainement les limites de la microélectronique à base de silicium a encouragé le développement de solutions alternatives. Parmi elles, l'électronique organique, dans laquelle les éléments actifs du composant sont constitués de systèmes organiques pi-conjugués, semble très prometteuse. Les progrès réalisés ces 20 dernières années sur les performances des dispositifs organiques résultent en grande partie de l'amélioration de la structuration de ces matériaux, et la relation entre structure et propriétés électroniques reste à ce jour l'une des problématiques majeures de l'électronique organique.Une caractérisation structurelle par STM de monocouches auto-assemblées réalisées à base de petites molécules synthétisées au laboratoire (B4OTF et B5OTF) ou de polythiophènes, a été entreprise dans un premier temps afin de dégager les mécanismes régissant l'assemblage des molécules. Dans le cas du polymère, une nette amélioration des propriétés cristallines a pu être obtenue par recuit des échantillons et une deuxième couche structurée a pu être observée pour la première fois sur des échantillons plus concentrés. Enfin l'influence de conformations locales inter ou intra-chaîne du polymère sur ses propriétés électronique intrinsèques a été investiguée par spectroscopie tunnel bidimensionnelle. S'il semble que les défauts intra-chaîne tels que les repliements aient peu d'impact sur la structure électronique du matériau, un surprenant accroissement du gap a été observé sur des chaînes isolées de deuxième couche qu'on suppose généralement en configuration de pi-stacking et donc susceptibles d'expérimenter une plus grande délocalisation électronique

Multi-scale X-ray computed-tomography for the 3D detection and location of nanomaterials in manufactured materials and complex media

International audienceX-ray computed tomography (CT) is a power-full 3D imaging technique for the in-situ and non-destructive investigation of the inner structure of an object. This relatively recent technique has tremendously evolved over the past decade with much more sensitive detec-tion systems and increased spatial resolution. Indeed it is now possible to reach spatial res-olution of tens of nanometers with synchro-tron X-ray source but also with lab-based systems (called nano-CT). Reaching such high spatial resolution made CT a valuable technique for the 3D detection and location of nanomaterials, their aggregates and agglomer-ates (NOAA) in manufactured materials (wood coating, polymers ..) and in complex and/or natural media (plants, organisms, or-gans …). The Nano-ID1 platform, installed at CEREGE (Aix en Provence, France), is equipped with two CT systems and offers the opportunity to perform multi-scale analysis on a same sam-ple, i.e. 3D imaging with a spatial resolution ranging from 50 µm to 50 nm. For example, in a study focusing on the aging of wood-coating containing CeO2 nanomateri-als and associated NOAA released, multi-scale micro and nano-CT gave the keys to identify NOAA distribution in non-aged mate-rials and their behavior during aging. In the field of “safer-by-design” production or eco-conception, the accurate distribution of NOAA and their residues in complex matrix-es is of particular interest to understand the the consumers and environmental exposure.We also demonstrated the relevance of multi-scale micro-CT (down to submicron-scale) to detect and locate CeO2-based NOAA within soft tissues (e.g. mouse lung tissues) after in vivo exposure and artefact-reduced sample preparation procedure. This capability is gaining interest especially since the scientific community cautiously address the potential risk of NOAA for humans and living organisms

Probing the electronic properties of self-organized poly(3-dodecylthiophene) monolayers by 2D STS imaging at the single chain scale

Regioregular poly(3-dodecylthiophene) films self-organized on highly oriented pyrolytic graphite have been investigated by scanning tunneling microscopy and two-dimensional scanning tunneling spectroscopy (STS). Simulated spectra in very good agreement with the experimental data have been obtained by a method combining ab initio and semiempirical approaches, which allows a careful discussion of the polymer electronic states. From the experimental data, with the support of modeling, it is shown that the STS spectra give a direct access to the polymer semiconducting band gap without noticeable charge-transfer effects from the substrate. Spectroscopic images are achieved at the single chain scale, which allows scrutinizing the electronic consequences of chain folds and π-stacking effects through spectroscopic contrasts. While chain folds do not locally increase the polymer band gap more than a few tens of millielectonvolt, a striking widening of the STS conductance gap is observed in the case of electronic tunneling through two interacting polymer layers. Scenarios based on nonplanar configuration of thiophene cycles within the second layer or variations of the charge screening effects are proposed to explain this phenomenon.This work has been supported by the French Ministry of Research under the grant “RTB: Post CMOS moléculaire 200 mm”. A. Rubio is supported by the Nanoquanta Network of Excellence (NMP4-CT-2004-500198), Spanish MCyT, and the Humboldt Foundation under the 2005 Bessel Award.Peer reviewe

Two-Dimensional Self-Assemblies of Thiophene−Fluorenone Conjugated Oligomers on Graphite: A Joint STM and Molecular Modeling Study

International audienc

Multi-scale X-ray computed-tomography for the 3D detection and location of nanomaterials in manufactured materials and complex media

International audienceX-ray computed tomography (CT) is a power-full 3D imaging technique for the in-situ and non-destructive investigation of the inner structure of an object. This relatively recent technique has tremendously evolved over the past decade with much more sensitive detec-tion systems and increased spatial resolution. Indeed it is now possible to reach spatial res-olution of tens of nanometers with synchro-tron X-ray source but also with lab-based systems (called nano-CT). Reaching such high spatial resolution made CT a valuable technique for the 3D detection and location of nanomaterials, their aggregates and agglomer-ates (NOAA) in manufactured materials (wood coating, polymers ..) and in complex and/or natural media (plants, organisms, or-gans …). The Nano-ID1 platform, installed at CEREGE (Aix en Provence, France), is equipped with two CT systems and offers the opportunity to perform multi-scale analysis on a same sam-ple, i.e. 3D imaging with a spatial resolution ranging from 50 µm to 50 nm. For example, in a study focusing on the aging of wood-coating containing CeO2 nanomateri-als and associated NOAA released, multi-scale micro and nano-CT gave the keys to identify NOAA distribution in non-aged mate-rials and their behavior during aging. In the field of “safer-by-design” production or eco-conception, the accurate distribution of NOAA and their residues in complex matrix-es is of particular interest to understand the the consumers and environmental exposure.We also demonstrated the relevance of multi-scale micro-CT (down to submicron-scale) to detect and locate CeO2-based NOAA within soft tissues (e.g. mouse lung tissues) after in vivo exposure and artefact-reduced sample preparation procedure. This capability is gaining interest especially since the scientific community cautiously address the potential risk of NOAA for humans and living organisms

Insight into mechanisms leading to the release of ceo2 nanoparticles embedded in an acrylic wood coating

The study of nanomaterials release from solid matrices is an emerging field of research. Until now most efforts have focused on quantifying and identifying the released objects, providing valuable inputs to risk assessment models. However the mechanisms lying behind release are still largely unknown and rarely investigated. Understanding release mechanisms of nano-objects is critical under two aspects. First of all it may allow predicting NOAA (Nano-objects, their aggregates and agglomerates) release based on a few material properties and may then reduce the need for costly and time-consuming testing. In a second time, unveiling release mechanism is key to implement a safe-by-design approach of nanotechnology. Once elucidated, physico-chemical processes leading to nanomaterial leaching can indeed be counterbalanced, to gain a better control on NOAA emissions. Nanomaterials have wide applications in paint and coating industry. They can improve rheological and mechanical properties of the products, confer them self-cleaning or antimicrobial capacity, or act as UV-absorber, stabilizing agents, pigments, etc. Along their life cycle paint and coatings will however experience processes that may lead to NOAA release. This is especially true for outdoor products, as sunlight and rain can induce very strong degradations. A weathering protocol in climatic chamber was developed at CEREGE, to evaluate NOAA releases from coatings under laboratory conditions. Alternating irradiation under Xe lamp (60W.m-2 in the 300nm-400nm range) and “rain” (=water spraying) phases were applied to an acrylic protective wood coating, enriched with CeO2 nanoparticles. Over a 3-months assay, significant emissions (> 1mg.m-2) of particulate CeO2 into water could be evidenced. A thorough characterization of wood samples was performed in order to understand the mechanisms leading to CeO2 release. Optical microscopy revealed the presence of cracks and blistering on weathered samples. It also showed an increase in paint porosity. In parallel, infrared spectroscopy and nuclear magnetic resonance were used to analyse chemical degradation of the acrylic polymer matrix. The overall distribution of CeO2 nanoparticles in the coating was assessed from results of X-ray fluorescence microscopy and laser-ablation-ICP-MS. Complementarily, direct size measurements on CeO2 aggregates incorporated in the wood coating were performed by micro and nano X-ray computed-tomography. They proved that aggregation of nanomaterials took place upon aging. Further transformation of ceria nanoparticles within the coating was evidenced by XANES, which showed partial reduction Ce(IV) to Ce(III) along the experiment. Based on this data, hypothesis on both the processes lying behind release and the form under which CeO2 is released is presented.into mechanisms leading to the release of ceo2 nanoparticles embedded in an acrylic wood coatin

Nanoscale Coloristic Pigments: Upper Limits on Releases from Pigmented Plastic during Environmental Aging, In Food Contact, and by Leaching

PMID: 28988475International audienceThe life cycle of nanoscale pigments in plastics may cause environmental or human exposure by various release scenarios. We investigated spontaneous and induced release with mechanical stress during/after simulated sunlight and rain degradation of polyethylene (PE) with organic and inorganic pigments. Additionally, primary leaching in food contact and secondary leaching from nanocomposite fragments with an increased surface into environmental media was examined. Standardized protocols/methods for release sampling, detection, and characterization of release rate and form were applied: Transformation of the bulk material was analyzed by Scanning Electron Microscopy (SEM), X-ray-tomography and Fourier-Transform Infrared spectroscopy (FTIR); releases were quantified by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), single-particle-ICP-MS (sp-ICP-MS), Transmission Electron Microscopy (TEM), Analytical Ultracentrifugation (AUC), and UV/Vis spectroscopy. In all scenarios, the detectable particulate releases were attributed primarily to contaminations from handling and machining of the plastics, and were not identified with the pigments, although the contamination of 4 mg/kg (Fe) was dwarfed by the intentional content of 5800 mg/kg (Fe as Fe2O3 pigment). We observed modulations (which were at least partially preventable by UV stabilizers) when comparing as-produced and aged nanocomposites, but no significant increase of releases. Release of pigments was negligible within the experimental error for all investigated scenarios, with upper limits of 10 mg/m2 or 1600 particles/mL. This is the first holistic confirmation that pigment nanomaterials remain strongly contained in a plastic that has low diffusion and high persistence such as the polyolefin High Density Polyethylene (HDPE)