Direct injection in organic SU8 nanowires and nanotubes for waveguiding properties investigation

International audienceWe report photonic concepts related to injection and sub-wavelength propagation in nanofibers (nanowires and nanotubes). These nanostructures are fabricated by the wetting template method leading to aspect ratio of over 250. At first, injection into nanowires and nanotubes of SU8, a photoresist used for integrated photonics, was successfully achieved by using polymer microlensed fibers with sub-micronic radius of curvature. Theoretical simulation by finite domain time-dependent (FDTD) method was used to determine the sub-wavelength propagation for nanowires and nanotubes and corroborate this coupling phenomena. The original confinment of energy density into SU8 nanotubes is highlighted. Finally, characterisation of propagation losses is reported by using a cut-back method transposed to such nanotubes and determined to range between 1 and 2 dB/mm. Both injection and cut-back method developed here are compatible with any sub-micronic structures. This work on SU8 nanofibers suggests broader perspectives for future nanophotonics

Design de nanofils luminescents organiques et hybrides à base de clusters de composés de métaux de transition

Le fort engouement pour les nanostructures luminescentes provient de leurs comportements émissifs originaux et de leur potentiel comme briques élémentaires pour de futurs dispositifs photoniques et optoélectroniques. Dans cette thèse, nous nous sommes intéressés au contrôle de la couleur d émission de nano-systèmes 1D organiques composés de deux types de luminophores. Dans une première partie, une famille peu connue de luminophores nanométriques a été étudiée: les clusters octaédriques de molybdène. Leur comportement photophysique et l ensemble des fréquences des modes de vibration de l entité Mo6Br14 ont été déterminés. Les spécificités de ces clusters ont été exploitées au sein de nanofils.Un premier type de nanofil coaxial synthétisé par méthode template a été conçu afin de séparer les deux types de luminophores. Les clusters (dans une matrice de PMMA) et le PPV ont été sélectionnés comme émetteurs rouge et vert respectivement, pour avoir une séparation spectrale. Le contrôle de la couleur sans transfert de charge ou d énergie entre les deux luminophores a été validé par l étude du comportement de photoluminescence stationnaire et résolue en temps, en accord avec un modèle phénoménologique. A l opposé, des nanofils exploitant deux polymères conjugués fluorescents (PFO bleu, F8T2 vert) comme système donneur-accepteur ont été élaborés. Leur mélange ou leur séparation en géométrie cœur-gaine a permis d explorer une nouvelle voie pour moduler les comportements excitoniques. Ces résultats montrent la versatilité des nanofils à base de polymère pour contrôler à l échelle nanométrique les comportements d émission de systèmes multi-luminophores.Luminescent organic nanostructures are of great importance as building blocks in future miniaturized photonic and optoelectronic devices because these systems rely upon the ability to tune and get new optical characteristics. One-dimensional luminescent nanostructures are new and promising systems with complex morphologies now available. In this work, we particularly investigated the control and the tuning of the emitted color of two-luminophore based nanowires. In a first part, an unfamiliar family of luminophore has been investigated: the octahedral molybdenum clusters. The vibrational modes frequencies of Mo6Br14 cluster were fully determined, as well as their photophysical properties. The unique features of these clusters were exploited into nanowires.Then, using a template method, we designed coaxial nanowires allowing the spatial separation of the two luminophores. The transition metal clusters in a PMMA matrix and PPV were selected as red and green emitters, respectively, to achieve the spectral separation. Remarkably, it was found from time-resolved photoluminescence study and confirmed by a phenomenological model that any charge or energy transfer is involved in this system.Alternatively, coaxial and blend designs were used to investigate and possibly tune energy/charge transfers involved in the donor-acceptor behavior of two conjugated polymers: PFO (blue emitter) and F8T2 (green emitter). These results demonstrate the great versatility of polymer-based nanowires to finely control at the nanoscale the emission features of multi-luminophore materials.LE MANS-BU Sciences (721812109) / SudocSudocFranceF

La participation des communautés locales à la marchandisation de la Nature

Depuis quelques années, les éléphants d’Afrique sont à nouveau menacés d’extinction par un braconnage intense et prolongé. L’article s’appuie sur le récit d’un braconnier du Rufiji (Tanzanie) pour examiner les déterminants de la participation villageoise au braconnage des éléphants et les articuler aux résultats de l’examen critique des politiques ultralibérales de conservation de la nature.Intense and protracted poaching over the past few years is again driving the African Elephant towards extinction. Based on the account of a poacher in Rufiji (Tanzania) we examine the factors that drive villagers to partake in elephant poaching and articulate these findings with a critical assessment of ultraliberal nature conservation policies

Appropriation des ressources « naturelles » et criminalisation des communautés paysannes

La plaine inondable du Rufiji (Tanzanie) est occupée par des populations dont les activités économiques principales sont l’agriculture vivrière et la pêche commerciale. Les revenus de la pêche légale assurent avec peine la sécurité alimentaire des foyers mais ne permettent pas de faire face à des dépenses « exceptionnelles ». Ainsi, pour financer les études secondaires de leurs enfants, les villageois n’ont guère d’autre choix que de quitter les zones de pêches légales et de pénétrer, au risque de leur vie, la Réserve de Chasse du Selous (50 000 km²) où se trouvent de nombreux lacs poissonneux. La Réserve, située à proximité immédiate des villages, s’est constituée progressivement au cours du XXe siècle par une série de décisions autoritaires et coercitives. Les communautés locales ne bénéficient d’aucune manière des revenus substantiels issus de son exploitation tandis qu’elles en supportent l’essentiel des coûts induits. Les nouvelles politiques de conservation « participatives » (community based conservation) mises en place depuis une dizaine d’années restent à l’état de déclarations d’intention.In Tanzania, the Rufiji floodplain is populated by people earning their living from agriculture and fishing. Revenues from legal fishing hardly secure food security of households, and don't really allow for other investments or expenses. In order for instance to earn enough money to pay for secondary school fees, many villagers actually need to leave the legal fishing zones and to penetrate in the Selous Reserve, where several lakes abounding in fish are situated. The Reserve has been progressively constituted throughout the twentieth century, but local villagers do not beneficiate from the revenues it generates. New "participatory" approaches and conservation policies are only declarations of interest without concrete effects

Sub-wavelength optical propagation in passive and active 1D-nanostructures

International audienceNanophotonics and biophotonics Track:6-4 Nanodevices and nanophotonics In the field of nanophotonics, the understanding of optical phenomena related to sub-wavelength guiding in 1D-nanostructures is a fundamental interest for devices down-scaling. We present theoretical and experimental investigation of light propagation in original passive and active organic nanotubes. For this, polymer nanotubes has been designed and developed by the template wetting method. To characterize their optical behavior and in particular the sub-wavelength propagation, numerical and experimental tools have been developed. Modelling phenomena propagating in these nanofibers was performed by the numerical FDTD method. The effects of the geometry of these nanotubes and nanowires have been investigated. In particular, the effect of the diameter (outer and inner diameter for nanotubes) on the propagation behavior (energy distribution, losses), as well as the effect of the substrate, have been determined. Experimentally, two types of nanofibers were studied. First, direct injection into passive nanofibers of SU8 polymer was performed through a microlensed optical fiber. A striking result is the assessment of optical losses measured by the cutback around 1.25 dB/mm for nanotubes of external and internal diameters respectively 240 nm and 120 nm. This appears very competitive compared to other systems currently envisaged for integratednanophotonics. Second, active polymer nanofibers (polyfluorene PFO) embedded in a waveguiding polymer were elaborated and appeared to be an efficient design for a nano-source

Sub-wavelength optical propagation in passive and active 1D-nanostructures

International audienceNanophotonics and biophotonics Track:6-4 Nanodevices and nanophotonics In the field of nanophotonics, the understanding of optical phenomena related to sub-wavelength guiding in 1D-nanostructures is a fundamental interest for devices down-scaling. We present theoretical and experimental investigation of light propagation in original passive and active organic nanotubes. For this, polymer nanotubes has been designed and developed by the template wetting method. To characterize their optical behavior and in particular the sub-wavelength propagation, numerical and experimental tools have been developed. Modelling phenomena propagating in these nanofibers was performed by the numerical FDTD method. The effects of the geometry of these nanotubes and nanowires have been investigated. In particular, the effect of the diameter (outer and inner diameter for nanotubes) on the propagation behavior (energy distribution, losses), as well as the effect of the substrate, have been determined. Experimentally, two types of nanofibers were studied. First, direct injection into passive nanofibers of SU8 polymer was performed through a microlensed optical fiber. A striking result is the assessment of optical losses measured by the cutback around 1.25 dB/mm for nanotubes of external and internal diameters respectively 240 nm and 120 nm. This appears very competitive compared to other systems currently envisaged for integratednanophotonics. Second, active polymer nanofibers (polyfluorene PFO) embedded in a waveguiding polymer were elaborated and appeared to be an efficient design for a nano-source

Deep red luminescent hybrid copolymer materials with high transition metal cluster content

Accepted 04 Dec 2013International audienceThe hybrid strategy is a powerful approach to design functional materials by combining inorganic dyes with an organic matrix. However, introducing high contents of inorganic species within the hybrid material is a real challenge that requires a perfect balance between the interactions of both components to avoid mainly phase segregation problems. Based on our demonstration on an anionic molybdenum cluster, we present a general method to introduce high contents of such class of nanometre sized inorganic molecular deep red dyes in a polymer matrix. Our strategy exploits the physical interactions between the organic and inorganic parts of the hybrid material and allows a high cluster rate to be introduced (up to 50 wt%) in the polymer matrix. The resulting hybrids are remarkably stable even after several months of ageing. Moreover, the Mo clusters maintain their intrinsic deep red luminescence properties while the polymer organic matrix fully maintains its processability, thanks to the di-anionic character of the Mo6 clusters. Such materials show promising prospects in applications needing deep red emitters

Transferable Integrated Optical SU8 Devices: From Micronic Waveguides to 1D-Nanostructures

International audienceWe report on optical components for integrated optics applications at the micro-and nanoscale. Versatile shapes and dimensions are achievable due to the liquid phase processability of SU8 resist. On the one hand, by adjusting the UV-lithography process, waveguiding structures are patterned and released from their original substrate. They can be replaced on any other substrate and also immerged in liquid wherein they still show off efficient light confinement. On the other hand, filled and hollow 1D-nanostructures are achievable by the wetting template method. By exploiting the large range of available SU8 viscosities, nanowires of diameter ranging between 50 nm and 240 nm, as well as nanotubes of controllable wall thickness are presented. Optical injection, propagation, and coupling in such nanostructures are relevant for highly integrated devices