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The dynamics of graphene growth on polycrystalline Pt foils during chemical vapor deposition (CVD) are investigated using in situ scanning electron microscopy and complementary structural characterization of the catalyst with electron backscatter diffraction. A general growth model is outlined that considers precursor dissociation, mass transport, and attachment to the edge of a growing domain. We thereby analyze graphene growth dynamics at different length scales and reveal that the rate-limiting step varies throughout the process and across different regions of the catalyst surface, including different facets of an individual graphene domain. The facets that define the domain shapes lie normal to slow growth directions, which are determined by the interfacial mobility when attachment to domain edges is rate-limiting, as well as anisotropy in surface diffusion as diffusion becomes rate-limiting. Our observations and analysis thus reveal that the structure of CVD graphene films is intimately linked to that of the underlying polycrystalline catalyst, with both interfacial mobility and diffusional anisotropy depending on the presence of step edges and grain boundaries. The growth model developed serves as a general framework for understanding and optimizing the growth of 2D materials on polycrystalline catalysts.

Nanostructured titanium dioxide is widely used for photovoltaic applications, primarily as electron transporting layer in perovskite and dye sensitized solar cells, basically due to suitable band gap for acceptance of electrons from active layer of solar cells. However, by combination of high reactivity of TiO 2 together with the large binding energy of ZnO, the process of electron transfer between the corresponding conduction and valence bands can be facilitated in the composite system. Different techniques have been reported for the growth of ZnO/TiO 2 nanocomposites in various forms. With the aim to prepare high performance TiO2@ZnO core–shell nanostructure for photovoltaic application, in this work TiO 2 was deposited on ZnO nanorods by pulsed laser deposition (PLD) and magnetron sputtering (MS). We studied influence of the preparation parameters to crystal structure and morphology of nanocomposite and correlate them with the optical and electrical properties. ZnO nanorods (ZNR) arrays were prepared by sol-gel procedure followed by annealing of nanorods to obtain crystallinity. TiO 2 thin films were prepared on ZNR using PLD in Ar or vakuum and by reactive MS with the aim to select the preference deposition procedure. The structural phase of TiO 2 were primary studied by confocal micro-Raman spectroscopy (mRS), while morphology and crystal structure on nanoscale were studied by high resolution transmission and scanning electron microscopy (HRTEM and HRSEM). The optical properties are evaluated by UV-vis spectroscopy, while for electrical characterization impedance spectroscopy was applied. Raman spectroscopy results indicated that TiO 2 thin films prepared by MS and PLD were amorphous after deposition. The annealing temperature for crystallization were optimised to obtain anatase structure, since mRS study showed the formation of rutile already at temperature between 450 and 500 °C. It was shown that morphology of the TiO 2 layers obtained by PLD considerably depend on preparation atmosphere and the number of pulses. In the case of preparation by MS the attention should be focused on reactive magnetron atmosphere as well as on the pre-treatment of the ZNR substrate. The obtained phase composition and morphology of the TiO 2 will be discussed in the frame of the preparation parameters, while optical and electrical properties of prepared TiO 2 @ZnO core–shell nanostructure will be discussed in the view of structure and morphology of the obtained TiO 2 layers. Acknowledgements: This work has been supported by Croatian Science Foundation under the project IP-2014-09-9419 and by Croatian-Germany DAAD bilateral project.

The thermally induced topotactic transformation of organic polymeric semiconductors is achieved using similarity of the chemical structures of the two C,N,H-containing materials. Namely, the oligomer of 3-aminotriazole-1,2,4 (OATA) is transformed into an electronically modified graphitic carbon nitride (OATA-CN) upon heating at 550 °C. During the transition, the flat band potential of the organic semiconductor is only slightly shifted from -0.11 eV to -0.06 eV, while the optical band gap is significantly expanded from 1.8 eV to 2.2 eV. The advantage of the suggested approach is the processability of the starting semiconductor combined with the minor morphology changes during the heat-treatment that enable preservation of the original oligomer micro- and macrostructures in the resulting carbon nitrides. As illustration, different OATA morphologies, including spherical nanoparticles, nanobarrels, nanowires and self-assembled macrospheres and composite sheets are synthesized and then transformed into OATA-CN with the retention of morphology. The surface area of the final carbon nitrides reaches 66 m2/g-1, without using any templates, auxiliary reagents or post treatment. As a consequence, the photocatalytic activity of the obtained carbon nitrides in the visible light driven hydrogen evolution is up to 5 times higher than measured for the reference bulk carbon nitride prepared by pyrolysis of melamine.

TiO2 is known as material with excellent chemical and photochemical stability was found that anatase is photocatalytically more active than rutile due to its large surface area. Ordered TiO2 nanostructures, including nanoparticles, nanotubes, and nanorods have garnered much research for their use in solar energy applications. In hybrid solar cells, the titania nanostructures accept electrons from photoexcited dye molecules or polymers adsorbed to the surface and direct the electrons into an external circuit. Hybrid solar cells with titania nanotubes have several advantages over other nanostructures and planar solar cells. The high surface area of nanotubes, compared to nanorods or flat surfaces, allows for more adsorption by electron donors such as molecular dyes and polymers, thus increasing solar photon absorption and charge collection (Roy 2011) [1]. In this research we will study different ways of modification of TiO2 nanotubes with the aim to increase solar absorbance and charge separation to increase efficiency for applications in solar cells. The nanotubes will be synthesized by electrochemical oxidation of Ti-foil. TiO2 nanotube arrays on substrates provide a superior platform for building up ordered heterojunctions for enhanced charge separation and electron transportation. The parameters of the TiO2 nanotubes will be finely tuned, allowing the optimization of device fabrication for different types of solar cells, such as DSSCs, hybrid solar cells.To obtained desired properties of the nanotubes, the nanotubes will be modified with BaTiO3 nanoparticles and dyes. For the structural characterization of all the titanate nanostructures we will used conventional and analytical transmission electron microscopy (TEM) techniques, scanning electron microscopy, XRD and Raman spectroscopy, and UV-Vis spectroscopy for measuring solar absorbance. With AFM we will study topography, ferroelectric and piezoelectric properties of obtained heterosctructures.

International audience; In coming years, due to climate change, the frequency of extraordinary events such as floods, tsunamis, mudslides, lahars, etc. might significantly increase. Given such a context, the existent protection against hazardous events is being challenged: individuals who are exposed to such adverse events need to decide whether or not to improve their level of protection. We investigate, experimentally, how a change in the intensity of an adverse event affects the level of collective protection chosen by individuals. For that purpose, we designed a within-subject experiment in which subjects were initially exposed to a sure adverse event followed by a random adverse event, both affecting negatively subjects’ payoffs. We compare three treatments that vary with respect to the specification of the random event: uniform risk, extreme risk, and ambiguity. The results show that for all treatments average group contributions increase significantly under randomness. Surprisingly however, not all subjects increased their contributions. More than a third of them reduced the level of their contribution, especially in the ambiguity treatment. Our results also show that depending on the type of adverse event, efficiency and group asymptotic convergences vary significantly. Efficiency is highest in the uniform risky treatment while the level of asymptotic group convergence is the lowest in the ambiguity treatment.

Diffusion du document : INRA Laboratoire d'Etudes et de Recherches économiques Rue de la Géraudière BP 71627 44316 Nantes Cedex 03 (FRA); Ce rapport a eu pour vocation de répondre aux deux premières phases d'une "entreprise d'évaluation", à savoir : (i) l'identification des acteurs en relation avec la nappe phréatique d'Alsace, et des effets sur ces derniers d'une évolution des caractéristiques de celle-ci, (ii) le recensement des méthodologies d'évaluation des différents services d'usages et de non-usages procurés par la nappe phréatique d'Alsace, en vue de l'établissement ultérieur de sa valeur économique totale, soit de sa valeur patrimoniale au sens où l'entendent les économistes. Aussi, les auteurs avaient deux objectifs principaux : réaliser un bilan détaillé des volumes prélevés annuellement sur la nappe phréatique d'Alsace et analyser les caractéristiques de différentes méthodes d'évaluation pouvant éventuellement être retenues dans une étude ultérieure portant sur la valeur patrimoniale de la nappe phréatique d'Alsace ou valeur économique totale. Au-delà des méthodes d'évaluation de chaque service offert par la nappe phréatique d'Alsace, la question reste entière quant à la définition d'un indicateur pertinent pour représenter la valeur patrimoniale ou valeur économique totale de cette dernière. Il conviendra donc d'apporter un soin immense à la résolution des problèmes d'agrégation de ces différentes valeurs à un instant donné.

Carbon deposition following thermal methane decomposition under dry and steam reforming conditions has been studied on yttria-stabilized zirconia (YSZ), Y2O3 and ZrO2 by a range of different chemical, structural and spectroscopic characterization techniques, including aberration-corrected electron microscopy, Raman spectroscopy, electric impedance spectroscopy and volumetric adsorption techniques. Concordantly, all experimental techniques reveal the formation of a conducting layer of disordered nanocrystalline graphite covering the individual grains of the respective pure oxides after treatment in dry methane at temperatures T ≥ 1000 K. In addition, treatment under moist methane conditions causes additional formation of carbon-nanotube-like architectures by partial detachment of the graphite layers. All experiments show that during carbon growth, no substantial reduction of any of the oxides takes place. Our results therefore indicate that these pure oxides can act as efficient nonmetallic substrates for methane-induced growth of different carbon species with potentially important implications regarding their use in solid oxide fuel cells. By comparison of the three oxides we could moreover elucidate differences in the methane reactivities of the respective SOFC-relevant purely oxidic surfaces under typical SOFC operation conditions without the presence of metallic constituents.

Efficient photocatalysis of various pollutants in the environment is a complex process and include so many factors, i.e. morphological factors as well as acid-base properties of the metal oxide and has significant contribution to the overall photocatalysis efficiency. In spite of numerous studies dealing with effect of inorganic ions which are mostly focused on the heavy metals adsorption as well as ion exchange mechanism there is lack of the data in the literature with basic findings about effect of the surface pH and the ionic strength on the TiO2 nanotubes and nanowires surfaces. Detailed information about acid-base surface properties are essential, because pH is one of the most important factor that have effects on the photocatalysis performance and efficient purification of the organic contaminants due to surface charge dependence of the pH as well as interfacial electron transfer and surface/interface polarisation effects in regard to the ESAB model.

International audience; We report the results of an experiment investigating the provision of a step-level collective good. This experiment compares the behavior of subjects in a public good game with the behavior of subjects in a club good game. In the club good game, players who do not contribute the membership fee are excluded from the consumption of the collective good. The introduction of a small membership fee has surprisingly strong effects: it increases the provision of the collective good, delays provision failures and increases the number of contributors. The experiment also reveals the limits of the introduction of a small fee. At a high threshold level, the membership fee no longer ensures successful provision.

National audience; Le risque de « lahars » est un des risques majeurs auxquels sont exposés les habitants d’Arequipa : plus d’un million d’habitants y serait directement soumis (Vargas-Franco et al., 2010). Le risque de « lahars » est un risque contre lesquels les individus exposés peuvent difficilement se protéger ou s’assurer à court terme. À long terme, mesures techniques et des solutions de régulation ont été mises en place (zonages des milieux soumis au risque, ouvrages hydrauliques de type barrages, etc.) et il existe la possibilité pour les individus de se relocaliser (l’opportunité de le faire dépendra en particulier de leur condition économique et sociale). Lorsque les individus sont confrontés à ce type de risque, non assurable et non diversifiable, on parle de « background risk » que l’on traduirait par « risque rémanent ». Par définition, un « background risk » est un risque non diversifiable, donc non assurable, et qui ne peut dès lors être partagé efficacement entre les individus d’une même communauté. Une question centrale, en présence de risque rémanent, est de savoir comment l’attitude des individus face au risque s’en trouve affectée et comment le partage de risques mutualisables s’en trouve modifié. Dans notre étude, nous nous intéressons principalement aux effets de la présence d’un risque rémanent (« background risk ») sur la prise de décision. L’objectif de notre étude est d’évaluer des éléments-clés d’une telle « demande » en fonction de trois paramètres qui sont : (1) leur perception du risque de « lahars » ; (2) leur attitude face à un risque et (3) leur impatience. Nous pourrons ainsi mettre en évidence comment la présence d’un « background risk » affecte l’attitude face au risque en comparant l’attitude d’individus exposés à un tel risque à celle d’individus non exposés à ce même type de risque. Dans ce but, nous utilisons deux outils complémentaires : l’enquête par questionnaires auprès de la population et des expériences d’économie de terrain. Les données issues des questionnaires montrent que les enquêtés (N=209) ne se sentent pas directement concernés par les risques naturels de manière générale. D’ailleurs, 94% des personnes enquêtées n’ont jamais mis en place de systèmes de sécurité pouvant les protéger (personnellement ou leur habitation) d’éventuels « lahars ». Cependant, malgré le fait que ce risque soit perçu comme « secondaire », les individus semblent bien informés sur les autorités à solliciter en cas de risque. Nos résultats expérimentaux montrent que les individus vivant dans des zones exposées ne sont pas significativement plus riscophobes que ceux vivant dans les zones non exposées, et ne sont pas significativement plus impatients. Mais les préférences déclarées par les individus à travers le questionnaire, montrent une différence significative dans la perception du risque entre les zones exposées et non exposées. Ces résultats ouvrent des perspectives méthodologiques et appliquées intéressantes.

This chapter provides an overview of legal and policy instruments that can be used to provide potential polluters with incentives for pollution abatement. The traditional law and economics literature as well as environmental economics are used to show how liability rules, safety regulation, environmental taxation, and emission trading all have specific advantages and disadvantages. It is therefore argued that environmental policy should look for optimal combinations (mixes) of a variety of policy instruments.