La diffusion et la pédagogie de l'information économique et sociale

2eme table ronde de la rencontre au palais d'Iéna à Paris dont le colloque s'intitule "l'information économique et sociale en France" datant du 21 janvier 1993. Cette séance s'est faite avec des journalistes représentant "Le Monde", "France Inter" et "Alternatives Economiques".Chapitre qui porte sur la manière dont les journalistes se représentent leur public, sur les représentations économiques de chacun, et la façon dont ils structurent ces représentations à leur manière

Structure, chemical analysis, and ferroelectric properties of chemical solution derived epitaxial PbZr0.2_{0.2}Ti0.8_{0.8}O3_3 films for nanomechanical switching

National audienceFerroelectrics are a material class characterized by the presence of a spontaneous polarization, which can be switched under electrical and mechanical stimuli. Switching phenomena is a complex process entangled to electronic, chemistry and (micro)structural properties, and intrinsic and extrinsic defects, all these phenomena happening within the ferroelectric object and at its physical boundaries. Considering these phenomena becomes critical in the framework of ferroelectric nanostructures, e.g. integrated thin films, where interfaces and surfaces effects dominate against volume related properties.Here we present the investigation of mechanical and electrical polarization switching on the prototypical tetragonal ferroelectric PbZr0.2Ti0.8O3 (PZT) thin films. Using different routes for chemical solution derived processing and rapid thermal annealing crystallization of epitaxial PZT thin films, we gain control over the electrical properties, chemistry and microstructure of thin films of different thickness. The ferroelectric properties obtained from microcapacitors underline that polarization switching behaviors under electric field are compatible with out-of-plane c-oriented tetragonal PZT, depicting remnant polarization values close to bulk ones for film thickness above 100 nm. Interestingly, a decrease of measured remnant polarization and larger leakage current are observed in capacitors based on films with thickness below 100 nm as well as in those undergoing different crystallization processes. To understand the nanoscale nature of the ferroelectric properties of these films, we used atomic force microscopy (AFM) derived techniques, i.e. piezoresponse force microscopy and local piezoelectric hysteresis loops [1]. Through application of voltage and/or pressure using the AFM-tip, within different electrical boundary conditions, we studied the nucleation and switching phenomena in as grown and in electrically and pressure-induced patterned ferroelectric domains. Results on the coercive electric fields and threshold forces required for polarization switching of PZT films are analyzed in view not only of the different electrical and mechanical poling, but also on the microstructure, film density, defects and chemical composition determined from X-ray diffraction, scanning electron transmission microscopy and electron energy loss spectroscopy, Rutherford backscattering and secondary ion mass spectroscopies.Polarization switching results of PZT films both at the micro- and nano-scales underline that the robust ferroelectric properties and switching mechanisms arise from reproducible chemistry, (micro)structure and defect distribution over thickness in chemical solution derived PZT films. These results will be discussed in the framework of integrated ferroelectric films for nanomechanical applications

Structure, chemical analysis, and ferroelectric properties of chemical solution derived epitaxial PbZr0.2_{0.2}Ti0.8_{0.8}O3_3 films for nanomechanical switching

National audienceFerroelectrics are a material class characterized by the presence of a spontaneous polarization, which can be switched under electrical and mechanical stimuli. Switching phenomena is a complex process entangled to electronic, chemistry and (micro)structural properties, and intrinsic and extrinsic defects, all these phenomena happening within the ferroelectric object and at its physical boundaries. Considering these phenomena becomes critical in the framework of ferroelectric nanostructures, e.g. integrated thin films, where interfaces and surfaces effects dominate against volume related properties.Here we present the investigation of mechanical and electrical polarization switching on the prototypical tetragonal ferroelectric PbZr0.2Ti0.8O3 (PZT) thin films. Using different routes for chemical solution derived processing and rapid thermal annealing crystallization of epitaxial PZT thin films, we gain control over the electrical properties, chemistry and microstructure of thin films of different thickness. The ferroelectric properties obtained from microcapacitors underline that polarization switching behaviors under electric field are compatible with out-of-plane c-oriented tetragonal PZT, depicting remnant polarization values close to bulk ones for film thickness above 100 nm. Interestingly, a decrease of measured remnant polarization and larger leakage current are observed in capacitors based on films with thickness below 100 nm as well as in those undergoing different crystallization processes. To understand the nanoscale nature of the ferroelectric properties of these films, we used atomic force microscopy (AFM) derived techniques, i.e. piezoresponse force microscopy and local piezoelectric hysteresis loops [1]. Through application of voltage and/or pressure using the AFM-tip, within different electrical boundary conditions, we studied the nucleation and switching phenomena in as grown and in electrically and pressure-induced patterned ferroelectric domains. Results on the coercive electric fields and threshold forces required for polarization switching of PZT films are analyzed in view not only of the different electrical and mechanical poling, but also on the microstructure, film density, defects and chemical composition determined from X-ray diffraction, scanning electron transmission microscopy and electron energy loss spectroscopy, Rutherford backscattering and secondary ion mass spectroscopies.Polarization switching results of PZT films both at the micro- and nano-scales underline that the robust ferroelectric properties and switching mechanisms arise from reproducible chemistry, (micro)structure and defect distribution over thickness in chemical solution derived PZT films. These results will be discussed in the framework of integrated ferroelectric films for nanomechanical applications

La diversité culturelle

La mondialisation est aujourd'hui une réalité bien installée, qui emporte hommes, sociétés et cultures. Mais avec quelles conséquences au juste pour la diversité culturelle ? Pour certains, la mondialisation conduirait à l'homogénéisation, à l'effacement des identités locales sous le poids de modèles imposés par les pays riches et par l'essor des moyens de communication. Pour d'autres, notre époque hypermoderne serait caractérisée par la fragmentation et la diversification des formes d'expression qui se développent par métissage, réaffirmation des cultures régionales ou réaction communautariste. Un ouvrage clair qui fait le point sur la question de la diversité culturelle, les débats et les enjeux qu'elle suscite

A multiscale study of the structure, chemistry and ferroelectric properties of epitaxial sol-gel PbZr0.2Ti0.8O3 films for nanomechanical switching

International audiencePolarization switching phenomena in ferroelectrics are complex processes entangled to electronic, chemical and (micro)(nano)structural properties, and intrinsic and extrinsic defects. These phenomena become critical in the framework of ferroelectric nanostructures, e.g. integrated thin films, where interface and surface effects dominate against volume-related properties.Here, we explore the mechanical and electrical polarization switching of ferroelectric thin films of the prototypical tetragonal ferroelectric PbZr0.2Ti0.8O3 (PZT). Using different parameters for sol-gel derived processing and rapid thermal annealing crystallization, we gain control over the electrical properties, chemistry and nanostructure of epitaxial PZT thin films of different thicknesses. The ferroelectric properties determined from microcapacitors indicate that polarization switching under electric field is compatible with out-of-plane c-oriented tetragonal PZT, depicting bulk-like remnant polarization values for films thicker than 100 nm. In capacitors based on films less than 100 nm thick as well as in those undergoing different crystallization processes, a decrease of the measured remnant polarization and the appearance of a leakage current are observed.Piezoresponse force microscopy was used to understand the nanoscale nature of the ferroelectric properties and the polarization switching under different stimuli of these films and environment. Through application of voltage and/or stress using the atomic force microscope tip, and under different electrical boundary conditions, we studied nucleation and switching phenomena in as-grown and in electrically and stress-induced patterned ferroelectric domains. Coercive electric fields and threshold forces required for polarization switching are not only dependent on the conditions of poling, but also on the structure, chemical and electronic properties, and concentration of defects, which we analyzed at different scales using X-ray diffraction and photoemission spectroscopy, scanning electron transmission microscopy, electron energy loss spectroscopy, and Rutherford backscattering and secondary ion mass spectrometry. Phase field simulations of PZT films depicting nanoscale defects support the experimental evidence of the significant contribution of the strain gradient leading to nanomechanical switching.Our results on polarization switching in epitaxial sol-gel derived PZT films will be discussed in the framework of integrated ferroelectric thin films and nanoscale ferroelectric switching for nanomechanical applications in stress sensors

A multiscale study of the structure, chemistry and ferroelectric properties of epitaxial sol-gel PbZr0.2Ti0.8O3 films for nanomechanical switching

International audiencePolarization switching phenomena in ferroelectrics are complex processes entangled to electronic, chemical and (micro)(nano)structural properties, and intrinsic and extrinsic defects. These phenomena become critical in the framework of ferroelectric nanostructures, e.g. integrated thin films, where interface and surface effects dominate against volume-related properties.Here, we explore the mechanical and electrical polarization switching of ferroelectric thin films of the prototypical tetragonal ferroelectric PbZr0.2Ti0.8O3 (PZT). Using different parameters for sol-gel derived processing and rapid thermal annealing crystallization, we gain control over the electrical properties, chemistry and nanostructure of epitaxial PZT thin films of different thicknesses. The ferroelectric properties determined from microcapacitors indicate that polarization switching under electric field is compatible with out-of-plane c-oriented tetragonal PZT, depicting bulk-like remnant polarization values for films thicker than 100 nm. In capacitors based on films less than 100 nm thick as well as in those undergoing different crystallization processes, a decrease of the measured remnant polarization and the appearance of a leakage current are observed.Piezoresponse force microscopy was used to understand the nanoscale nature of the ferroelectric properties and the polarization switching under different stimuli of these films and environment. Through application of voltage and/or stress using the atomic force microscope tip, and under different electrical boundary conditions, we studied nucleation and switching phenomena in as-grown and in electrically and stress-induced patterned ferroelectric domains. Coercive electric fields and threshold forces required for polarization switching are not only dependent on the conditions of poling, but also on the structure, chemical and electronic properties, and concentration of defects, which we analyzed at different scales using X-ray diffraction and photoemission spectroscopy, scanning electron transmission microscopy, electron energy loss spectroscopy, and Rutherford backscattering and secondary ion mass spectrometry. Phase field simulations of PZT films depicting nanoscale defects support the experimental evidence of the significant contribution of the strain gradient leading to nanomechanical switching.Our results on polarization switching in epitaxial sol-gel derived PZT films will be discussed in the framework of integrated ferroelectric thin films and nanoscale ferroelectric switching for nanomechanical applications in stress sensors