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Search Results: 1 - 10 of 5831 matches for " Robin Thierry "
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Three dimensional cooling and trapping with a narrow line
Thierry Chaneliere,Ling Xiang He,Robin Kaiser,David Wilkowski
Physics , 2007, DOI: 10.1140/epjd/e2007-00329-8
Abstract: The intercombination line of Strontium at 689nm is successfully used in laser cooling to reach the photon recoil limit with Doppler cooling in a magneto-optical traps (MOT). In this paper we present a systematic study of the loading efficiency of such a MOT. Comparing the experimental results to a simple model allows us to discuss the actual limitation of our apparatus. We also study in detail the final MOT regime emphasizing the role of gravity on the position, size and temperature along the vertical and horizontal directions. At large laser detuning, one finds an unusual situation where cooling and trapping occur in the presence of a high bias magnetic field.
MOCVD growth mechanisms of ZnO nanorods
Guillaume Perillat-Merceroz,Pierre-Henri Jouneau,Guy Feuillet,Robin Thierry,Milan Rosina,Pierre Ferret
Physics , 2011, DOI: 10.1088/1742-6596/209/1/012034
Abstract: ZnO is a promising material for the fabrication of light emitting devices. One approach to achieve this goal is to use ZnO nanorods because of their expected high crystalline and optical quality. Catalyst free growth of nanorods by metalorganic chemical vapour deposition (MOCVD) was carried out on (0001) sapphire substrates. Arrays of well-aligned, vertical nanorods were obtained with uniform lengths and diameters. A thin wetting layer in epitaxy with the sapphire substrate is formed first, followed by pyramids and nanorods. The nucleation of nanorods occurs either directly at the interface, or later on top of some of the pyramids, suggesting various nucleation mechanisms. It is shown that crystal polarity plays a critical role in the growth mechanism with nanorods of Zn polarity and their surrounding pyramids with O polarity. A growth mechanism is proposed to explain that most threading dislocations lie in the wetting layer, with only a few in the pyramids and none in the nanorods.
Structural recovery of ion implanted ZnO nanowires
Guillaume Perillat-Merceroz,Fabrice Donatini,Robin Thierry,Pierre-Henri Jouneau,Pierre Ferret,Guy Feuillet
Physics , 2012, DOI: 10.1063/1.4704697
Abstract: Ion implantation is an interesting method to dope semiconducting materials such as zinc oxide provided that the implantation-induced defects can be subsequently removed. Nitrogen implantation followed by anneals under O2 were carried out on zinc oxide nanowires in the same conditions as in a previous study on bulk ZnO [J. Appl.Phys. 109, 023513 (2011)], allowing a direct comparison of the defect recovery mechanisms. Transmission electron microscopy and cathodoluminescence were carried out to assess the effects of nitrogen implantation and of subsequent anneals on the structural and optical properties of ZnO nanowires. Defect recovery is shown to be more effective in nanowires compared with bulk material due to the proximity of free surfaces. Nevertheless, the optical emission of implanted and annealed nanowires deteriorated compared to as-grown nanowires, as also observed for unimplanted and annealed nanowires. This is tentatively attributed to the dissociation of excitons in the space charge region induced by O2 adsorption on the nanowire surface.
Strain relaxation by dislocation glide in ZnO/ZnMgO core-shell nanowires
Guillaume Perillat-Merceroz,Robin Thierry,Pierre-Henri Jouneau,Pierre Ferret,Guy Feuillet
Physics , 2012, DOI: 10.1063/1.4704927
Abstract: Plastic relaxation of the misfit stress in core-shell semi-conducting nanowires can lead to structural defects, detrimental to applications. Core-shell Zn{0.7}Mg{0.3}O/ZnO quantum well heterostructures were deposited on ZnO nanowires. Strain along the a and c axes of the wurtzite structure is relaxed through the glide of dislocation half-loops from the free surfaces, within pyramidal and prismatic planes. Some half-loops are closed up in the barriers to accommodate the misfit at two consecutive interfaces of the quantum well stack. Dislocations are also observed within the nanowire core: contrary to two-dimensional structures, both the core and the shell can be plastically relaxed.
Core-shell multi-quantum wells in ZnO / ZnMgO nanowires with high optical efficiency at room temperature
Robin Thierry,Guillaume Perillat-Merceroz,Pierre-Henri Jouneau,Pierre Ferret,Guy Feuillet
Physics , 2013, DOI: 10.1088/0957-4484/23/8/085705
Abstract: Nanowire-based light-emitting devices require multi-quantum well heterostructures with high room temperature optical efficiencies. We demonstrate that such efficiencies can be attained through the use of ZnO/Zn(1-x)MgxO core shell quantum well heterostructures grown by metal organic vapour phase epitaxy. Varying the barrier Mg concentration from x=0.15 to x=0.3 leads to the formation of misfit induced dislocations in the multi quantum wells. Correlatively, temperature dependant photoluminescence reveals that the radial well luminescence intensity decreases much less rapidly with increasing temperature for the lower Mg concentration. Indeed, about 54% of the 10K intensity is retained at room temperature with x=0.15, against 2% with x=0.30. Those results open the way to the realization of high optical efficiency nanowire-based light emitting diodes.
Compared growth mechanisms of Zn-polar ZnO nanowires on O-polar ZnO and on sapphire
Guillaume Perillat-Merceroz,Robin Thierry,Pierre-Henri Jouneau,Pierre Ferret,Guy Feuillet
Physics , 2013, DOI: 10.1088/0957-4484/23/12/125702
Abstract: Controlling the growth of zinc oxide nanowires is necessary to optimize the performances of nanowire-based devices such as photovoltaic solar cells, nano-generators, or light-emitting diodes. In this view, we investigate the nucleation and growth mechanisms of ZnO nanowires grown by metalorganic vapor phase epitaxy either on O-polar ZnO or on sapphire substrates. Whatever the substrate, ZnO nanowires are Zn-polar, as demonstrated by convergent beam electron diffraction. For growth on O-polar ZnO substrate, the nanowires are found to sit on O-polar pyramids. As growth proceeds, the inversion domain boundary moves up in order to remain at the top of the O-polar pyramids. For growth on sapphire substrates, the nanowires may also originate from the sapphire / ZnO interface. The presence of atomic steps and the non-polar character of sapphire could be the cause of the Zn-polar crystal nucleation on sapphire, whereas it is proposed that the segregation of aluminum impurities could account for the nucleation of inverted domains for growth on O-polar ZnO.
An extra-heating mechanism in Doppler-cooling experiments
Thierry Chaneliere,Jean-Louis Meunier,Robin Kaiser,Christian Miniatura,David Wilkowski
Physics , 2004, DOI: 10.1364/JOSAB.22.001819
Abstract: In this paper we experimentally and theoretically investigate laser cooling of Strontium 88 atoms in one dimensional optical molasses. In our case, since the optical cooling dipole transition involves a $J_g=0$ groundstate, no Sisyphus-type mechanisms can occur. We are thus able to test quantitatively the predictions of the Doppler-cooling theory. We have found, in agreement with other similar experiments, that the measured temperatures are systematically larger than the theoretical predictions. We quantitatively interpret this discrepancy by taking into consideration the extra-heating mechanism induced by transverse spatial intensity fluctuations of the optical molasses. Experimental data are in good agreement with Monte-Carlo simulations of our theoretical model. We thus confirm the important role played by intensity fluctuations in the dynamics of cooling and for the steady-state regime.
Aging and the decline in health  [PDF]
Robin Holliday
Health (Health) , 2010, DOI: 10.4236/health.2010.26092
Abstract: The biological reasons for aging are now understood. Aging is the result of multiple stochastic events in molecules, cells, tissues and organs. These together produce the aged phenotype, senescence and ultimately death. Many of these changes can be directly linked to specific age-associated disease. However, there are also age-related changes that are not pathological. It can be said that aging has multiple causes, or is instead due to a general loss of molecular fidelity, that is, an increase in disorder. The complexity of organism means that they develop as ordered structures by obtaining energy from the environment. These ordered structures must be maintained by a wide variety of mechanisms which also depend on energy resources. Eventually these mechanisms fail, and senescence sets in. It is known that the efficiency of maintenance is correlated directly with the lifespan of different mammalian species. Also, these lifespans are inversely correlated with fecundity or reproductive potential. There is a trade off between investment of resources in maintenance of the body, or soma, and investment in reproduction.
The Alarmin Concept Applied to Human Renal Transplantation: Evidence for a Differential Implication of HMGB1 and IL-33
Antoine Thierry, Sébastien Giraud, Aurélie Robin, Anne Barra, Franck Bridoux, Virginie Ameteau, Thierry Hauet, Jean-Philippe Girard, Guy Touchard, Jean-Marc Gombert, André Herbelin
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0088742
Abstract: The endogenous molecules high mobility group box 1 (HMGB1) and interleukin-33 (IL-33) have been identified as alarmins, capable of mediating danger signals during tissue damage. Here, we address their possible role as innate-immune mediators in ischemia-reperfusion injury (IRI) following human kidney transplantation. We analysed serum and urinary HMGB1 and IL-33 levels, all determined by enzyme-linked immunosorbent assay, in a cohort of 26 deceased renal transplant recipients. Urinary HMGB1 and IL-33 levels were significantly increased as soon as 30 min after reperfusion, as compared to those before treatment. Moreover, both serum and urinary IL-33 (but not HMGB1) increase was positively correlated with cold ischemia time, from 30 min to 3 days post-transplantation. In vitro, human umbilical vein endothelial cells subjected to hypoxia conditions released both HMGB-1 and IL-33, while only the latter was further increased upon subsequent re-oxygenation. Finally, we postulate that leukocytes from renal recipient patients are targeted by both HMGB1 and IL-33, as suggested by increased transcription of their respective receptors (TLR2/4 and ST2L) shortly after transplantation. Consistent with this view, we found that iNKT cells, an innate-like T cell subset involved in IRI and targeted by IL-33 but not by HMGB1 was activated 1 hour post-transplantation. Altogether, these results are in keeping with a potential role of IL-33 as an innate-immune mediator during kidney IRI in humans.
Photodarkening of Infrared Irradiated Yb3+-Doped Alumino-Silicate Glasses: Effect on UV Absorption Bands and Fluorescence Spectra
Hrvoje Gebavi,Daniel Milanese,Stefano Taccheo,David Mechin,Achille Monteville,Francesca S. Freyria,Barbara Bonelli,Thierry Robin
Fibers , 2013, DOI: 10.3390/fib1030101
Abstract: The photodarkening phenomenon in alumino-silicate glass preforms, doped with different ytterbium concentrations, was studied. The UV band, comprised between 180 and 350 nm, was examined before and after irradiation at 976 nm. The non-linear dependence of 240 nm band with concentration after infra-red irradiation was demonstrated and ascribed predominantly to Yb 3+ pair’s interaction. The emission spectrum after the excitation in UV spectral region showed increased intensity after photodarkening, probably due to Yb 2+ ions creation. Phenomenological photodarkening model and the possible existence of several defect types are presented.
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