In situ bending of an Au nanowire monitored by micro Laue diffraction

International audienceThis article reports on the first successful combination of micro Laue (µLaue) diffraction with an atomic force microscope for in situ nanomechanical tests of individual nanostructures. In situ three-point bending on self-suspended gold nanowires was performed on the BM32 beamline at the ESRF using a specially designed atomic force microscope. During the bending process of the self-suspended wire, the evolution of µLaue diffraction patterns was monitored, allowing for extraction of the bending angle of the nanowire. This bending compares well with finite element analysis taking into account elastic constant bulk values and geometric nonlinearities. This novel experimental setup opens promising perspectives for studying mechanical properties at the nanoscale

Untangling natural variability of macrofaunal populations from protection effects

Marine protected areas are essential for conservation purposes. Remarkably, few studies have assessed the responses of small macrofaunal species to different protection levels in the Mediterranean Sea. Using a hierarchical sampling design spanning four orders of magnitude (1, 10, 100 and 1000 m), we investigated whether a marine protected area had an effect on crustacean (amphipod) and mollusc (mainly gastropod) assemblages associated with Posidonia oceanica seagrass meadows. Based on this investigation, we report spatial and temporal variability patterns of these assemblages in four different protection levels. We also discuss potential confounding effects on these areas, such as different habitat features. The structure of amphipod and gastropod assemblages based on density data was patchy at small and large spatial scales, and differed markedly among protection levels. Multiscale analyses showed that lower densities and/or biomasses of several taxa occurred within fully protected areas when compared to partially protected areas. Moreover, the seagrass meadows accounted for a low proportion of the total variability of the studied macrofaunal assemblages. We suggest therefore that the observed patchiness is likely to occur for multiple and interrelated reasons, ranging from the ecological and behavioural traits (e.g., dispersion and mobility) of macrofaunal species to protection-dependent factors such as fish predation. Multiscale spatial and temporal monitoring of macrofaunal assemblages in a long-term perspective, as well as experimental manipulations, are needed to better understand the protection effects

Structural and optical analyses of GaP/Si and (GaAsPN/GaPN)/GaP/Si nanolayers for integrated photonics on silicon

International audienceWe report a structural study of molecular beam epitaxy-grown lattice-matched GaP/Si(0 0 1) thin layers with an emphasis on the interfacial structural properties, and optical studies of GaAsP(N)/GaP(N) quantum wells coherently grown onto the GaP/Si pseudo substrates, through a complementary set of characterization tools. Room temperature photoluminescence at 780 nm from the (GaAsPN/GaPN) quantum wells grown onto a silicon substrate is reported. Despite this good property, the time-resolved photoluminescence measurements demonstrate a clear influence of non-radiative defects initiated at the GaP/Si interface. It is shown from simulations, how x-ray diffraction can be used efficiently for analysis of antiphase domains. Then, qualitative and quantitative analyses of antiphase domains, micro-twins, and stacking faults are reported using complementarity of the local transmission electron microscopy and the statistical x-ray diffraction approaches

Structural charaterisation of GaP/Si nanolayers

International audienceGrowth of GaP (III-V semiconductor) directly deposited on Si has been proposed to overcome the problems of lattice mismatch, in the context of monolithic integration of photonics on silicon. [1] However, long-term stable device per-formance implies reproducible achievement of defect-free interfaces between III-V and Si. Among them, antiphase do-mains (APD) and microtwins (MT) are quite difficult to avoid. And characterization means sensitive to these defects must employed for optimization of the growth pocess and qualification of the grown layers. Lab setup and synchrotron XRD is combined with TEM and AFM osbervations

structural characterization of MBE grown GaP/Si nanolayers

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Quantitative study of microtwins in GaP/Si thin film and GaAsPN quantum wells grown on silicon substrates

original title in MBE 2012 : "Structural and optical studies of GaP/Si induced defects in GaAsPN quantum wells grown on Si"International audienceWe report on the quantitative study of microtwins (MT) defects in the GaP/Si(0 0 1) thin film grown by Molecular Beam Epitaxy and the optical properties of GaAsP(N)/GaP(N) quantum wells grown on top of the GaP/Si pseudo-substrates. A 780 nm photoluminescence at room temperature from the GaAsPN quantum wells is measured on silicon. Time-resolved photoluminescence has been performed and evidences the influence of non-radiative defects originated from the GaP/Si interface. The structural defects such as MT are quantitatively analyzed by synchrotron X-ray diffraction (XRD) combined with transmission electron microscopy (TEM) analyses. We show that the XRD measurements are in good agreement with TEM observation and reveal a strong contribution of MT in the [1 1 1] direction. The MT density appears to be directly correlated with the growth temperature

Coherent integration of photonics on silicon through the growth of nanostructures on GaP/Si

International audienceSelected results obtained in the framework of MBE grown nanostructure for photonics on silicon are repsented in this paper. We present first a comprehensive study of GaAsPN/GaPN quantum wells (QWs) grown onto GaP substrates, in the light of a comparison with their N-free GaAsP/GaP QWs counterpart system. High density of small InGaAs/GaP Quantum Dots are presented next with their PL properties. Finally, RT photoluminescence properties of GaAsPN/GaPN QWs onto Si substrate are presented and discussed in term of carrier injection efficiency. However, for future development, optical properties of the active area must be improved and are tightly bound to the structural perfection of the GaP/Si template layer. To address this point, structural analyses including X-Ray Diffraction (lab setup and synchrotron) and Transmission Electron Microscopy have been performed, with a particular care for typical III-V/Si defect characterisation. First results of Si buffer layer growth are also presented as a perspective for future low defect MBE grown GaP/Si template layers

Structural characterisation of GaP/Si nanolayers

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Mercury species export from the Arctic to the Atlantic Ocean

Highlights • First full water column measurements of tHg, pHg, MMHg, MeHg, and DGM at the Fram Strait. • The Arctic Ocean exports tHg- and MeHg-enriched waters to the North Atlantic Ocean. • The Arctic Ocean exports about 18 Mg y−1 of tHg to the Nordic Seas and North Atlantic. • About 40% of exported tHg is in the form of MeHg. The Fram Strait is the only deep connection between the Arctic and Atlantic Oceans. The main water and mercury (Hg) fluxes between these oceans occur via the Fram Strait and Barents Sea Opening. Several Hg mass balance studies indicated a net Hg export from the Arctic to the Atlantic Ocean. However, in the absence of Hg measurements in the Fram Strait and Barents Sea Opening, these estimates were based on North Atlantic and central Arctic Ocean data alone. Here, we refine the Arctic total Hg (tHg) and methylated Hg (MeHg) mass budgets using new data acquired during the 2015 GEOTRACES (section GN04) TransArcII cruise in the Barents Sea Opening and the 2016 GEOTRACES (section GN05) GRIFF cruise, which covered the Fram Strait and Northeast Greenland Shelf. Total Hg increased westward along the Fram Strait transect, reaching the highest concentrations on the Northeast Greenland Shelf. Concentrations of tHg averaged 1.29 ± 0.43 pM in the East Greenland Current, while core waters of the West Spitsbergen Current had average values of 0.80 ± 0.26 pM. Using our new data, we estimate that 43 ± 9 Mg y−1 of tHg is transported to the Arctic Ocean in the core of the West Spitsbergen Current, while 54 ± 13 Mg y−1 of tHg is exported from the Arctic Ocean in the East Greenland Current and Recirculated Atlantic Water. This results in a net tHg export of 11 ± 8 Mg y−1via the Fram Strait. We find a shallow MeHg maximum (at 150 m depth) in the East Greenland Current, in agreement to what was reported for the central Arctic Ocean and Canadian Arctic Archipelago. The West Spitsbergen Current is characterized by lower MeHg concentrations and a deeper MeHg maximum, that is located at approximately 1000 m depth. We estimate a net MeHg export of 6 ± 2 Mg y−1 from the Arctic Ocean via the Fram Strait, which is nearly half of the exported tHg. Most of the exported MeHg is in the form of DMHg (2:1 ratio of dimethylmercury to monomethylmercury). Previous studies reported lower MeHg proportions. Our observations show that the Arctic Ocean is producing and exporting MeHg to the Atlantic Ocean. In total, the Arctic Ocean exports about 18 Mg y−1 of tHg to the Nordic Seas and North Atlantic via the Fram Strait and Davis Strait, of which 7.5 Mg y−1 is in the MeHg form