Low temperature reflectivity study of ZnO/(Zn,Mg)O quantum wells grown on M-plane ZnO substrates

We report growth of high quality ZnO/Zn0.8Mg0.2O quantum well on M-plane oriented ZnO substrates. The optical properties of these quantum wells are studied by using reflectance spectroscopy. The optical spectra reveal strong in-plane optical anisotropies, as predicted by group theory, and marked reflectance structures, as an evidence of good interface morphologies. Signatures ofc onfined excitons built from the spin-orbit split-off valence band, the analog of exciton C in bulk ZnO are detected in normal incidence reflectivity experiments using a photon polarized along the c axis of the wurtzite lattice. Experiments performed in the context of an orthogonal photon polarization, at 90^{\circ}; of this axis, reveal confined states analogs of A and B bulk excitons. Envelope function calculations which include excitonic interaction nicely account for the experimental report

Drop impact dynamics on slippery liquid-infused porous surfaces: influence of oil thickness

Slippery liquid-infused porous surfaces (SLIPS) are porous nanostructures impregnated with a low surface tension lubricant. They have recently shown great promise in various applications that require non-wettable superhydrophobic surfaces. In this paper, we investigate experimentally the influence of the oil thickness on the wetting properties and drop impact dynamics of new SLIPS. By tuning the thickness of the oil layer deposited through spin-coating, we show that a sufficiently thick layer of oil is necessary to avoid dewetting spots on the porous nanostructure and thus increasing the homogeneity of the liquid distribution. Drop impact on these surfaces is investigated with a particular emphasis on the spreading and rebound dynamics when varying the oil thickness and the Weber number

Plastic flow and structural heterogeneities in silicate glasses - A high throughput investigation

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Is the second harmonic method applicable for thin films mechanical properties characterization by nanoindentation? Is the second harmonic method applicable for thin films mechanical properties characterization by nanoindentation?

The second harmonic method is a dynamic indentation technique independent of the direct indentation depth measurement. It can be used to determine near-surface mechanical properties of bulk materials more precisely than classical dynamic nano-indentation. In this paper, the second harmonic method is extended to the measurement of the mechanical properties of thin PMMA layers deposited onto silicon wafers. It is shown that this new technique gives precise results at small depths (less than 100nm), even for films with a thickness lower than 500nm, which was not possible to achieve with the classical CSM method. However, experimental and numerical results obtained both with classical nanoindentation and second harmonic methods differ at high indentation depth. Using FE simulations and AFM measurements, it is shown that the contact depth calculation with classical models can explain this difference

Micro-pillar testing of amorphous silica

International audienceAmorphous silica exhibits a complex mechanical response. The elastic regime is highly non linear while plastic flow does not conserve volume, re- sulting in densification. As a result the quantification of a reliable constitutive equation is a difficult task. We have assessed the potential of micro-pillar compression testing for the investigation of the micromechanical properties of amorphous silica. We have calculated the response of amorphous silica mi- cropillars as predicted by Finite Element Analysis. The results were compared to preliminary micro-compression tests. In the calculations an advanced con- stitutive law including plastic response, densification and strain hardening was used. Special attention was paid to the evaluation of the impact of substrate compliance, pillar misalignment and friction conditions. We find that amor- phous silica is much more amenable than some metals to microcompression experiments due to a comparatively high ratio between yield stress and elastic modulus. The simulations are found to be very consistent with the experimen- tal results. However full agreement cannot be obtained without allowance for the non linear response of amorphous silica in the elastic regime

Exploring high repetitivity remote sensing time series for mapping and monitoring natural habitats ; A new approach combining OBIA and k-partite graphs

International audienc

About the plastic response of silicate glasses at the micronscale

Despite their brittleness, silicate glasses undergo plastic deformation at the micron scale. Mechanical contact and indentation are the most common situations of interest. The plasticity of glasses is characterized not only by shear flow but also by a permanent densification process. We present novel observations of the deformation and fracture of amorphous silica micropillars of various sizes using In Situ SEM Micro-Compression (Fig 1), that can help better understand the mechanisms occurring prior to its fracture [1]. Exhibiting one of the highest ratios of shear stress on shear modulus, fused silica thus further distinguishes itself from other amorphous materials. Moreover, nanocompression allows successful observations of crack initiation and growth. In parallel to this experimental investigation, atomistic simulations [2] aiming to investigate the theoretical plastic response of silicate glasses under coupled shear-pressure stress state was run. The results were interpreted in terms of volumetric and shear hardening. A buckling-like behaviour is clearly evidenced at low density (large free-volume) whereas a BMG-like is observed for samples densified until saturation. Thanks to this rich set of data, it seems now possible to define a constitutive model taking into account both nanomechanical results, i.e. nanopillars, nanoindentation, diamond anvil cell, and molecular dynamics simulation Despite their brittleness, silicate glasses undergo plastic deformation at the micron scale. Mechanical contact and indentation are the most common situations of interest. The plasticity of glasses is characterized not only by shear flow but also by a permanent densification process. We present novel observations of the deformation and fracture of amorphous silica micropillars of various sizes using In Situ SEM Micro-Compression (Fig 1), that can help better understand the mechanisms occurring prior to its fracture [1]. Exhibiting one of the highest ratios of shear stress on shear modulus, fused silica thus further distinguishes itself from other amorphous materials. Moreover, nanocompression allows successful observations of crack initiation and growth. In parallel to this experimental investigation, atomistic simulations [2] aiming to investigate the theoretical plastic response of silicate glasses under coupled shear-pressure stress state was run. The results were interpreted in terms of volumetric and shear hardening. A buckling-like behaviour is clearly evidenced at low density (large free-volume) whereas a BMG-like is observed for samples densified until saturation. Thanks to this rich set of data, it seems now possible to define a constitutive model taking into account both nanomechanical results, i.e. nanopillars, nanoindentation, diamond anvil cell, and molecular dynamics simulation

GaN-AlGaN Heterostructure Field-Effect Transistors over Bulk GaN Substrates

We report on AlGaN/GaN heterostructures and heterostructurefield-effect transistors(HFETs) fabricated on high-pressure-grown bulk GaN substrates. The 2delectron gas channel exhibits excellent electronic properties with room-temperature electron Hall mobility as high as μ=1650 cm2/V s combined with a very large electron sheet density ns≈1.4×1013 cm−2.The HFET devices demonstrated better linearity of transconductance and low gate leakage, especially at elevated temperatures. We also present the comparative study of high-current AlGaN/GaN HFETs(nsμ\u3e2×1016 V−1 s−1) grown on bulk GaN, sapphire, and SiC substrates under the same conditions. We demonstrate that in the high-power regime, the self-heating effects, and not a dislocation density, is the dominant factor determining the device behavior

The DACAPO-PESO campaign: Dynamics, Aerosol, Cloud and Precipitation Observations in the Pristine Environment of the Southern Ocean: An overview

This article gives an overview of the DACAPO-PESO field experiment, which has taken place in Punta Arenas, Chile, from November 2018 to November 2021, and showcases first exciting research results that have already emerged from it.In diesem Artikel wird ein Überblick über das DACAPO-PESO Experiment gegeben, welches von November 2018 bis November 2021 in Punta Arenas, Chile, stattgefunden hat. Außerdem werden erste spannende Forschungsergebnisse vorgestellt, die bereits daraus gewonnen wurden