In article number 1900164 by Abdallah Ougazzaden and co‐workers, III‐Nitride based LEDs have been locally grown on h‐BN and fabricated at a wafer‐scale. This enables a simple and a dicing‐free pick‐and‐place of the devices on a flexible substrate without performance degradation.

Soft adhesion to a horizontal flat substrate of micron-sized colloids coated by acontrolled molar fraction f of PLL-g-PNIPAM is tuned and triggered by controllingthe temperature of the sample. This mechanism is possible becausePNIPAM is a thermo-responsive polymer, which undergoes a phase transitionat a LCST (lower critical solution temperature) Tc = 32 +- 1°C. In order tocapture the very final events before the immobilization of colloids the T-rampprotocol is designed: the particles suspension is injected in cell at room temperature,the temperature is increased at a constant rate up to 38°C> Tc, andkept constant until the end of the acquisition. Attraction between beads andthe flat substrate is thereby triggered when crossing the critical temperatureTc. Ascending and descending ramp experiments are performed in order to accessboth adsorption and desorption kinetics. 3-D motion of beads is real-timetracked using slightly defocused microscopy in parallel illumination. We usetrack records to have access to pre-adsorption dffusion coeffcients and to characterizeadsorption and desorption dynamics. Present results corroborate thatadsorption is controlled by PNIPAM doping, and indeed dominated by rollingand memory (aging) effect on the contact domain. On the contrary, the desorption kinetics is independent of doping. Moreover, the sharpness (in T) ofthe PNIPAM transition is quantified in a set of experiments at different rampspeeds. We show that the transition smearing can reach up to +-1°C for higherPNIPAM coverage, while it is not detectable for the lowest ones. The combinationof all these observations paves the way to practical applications. Asan example, we will discuss a soft adhesion-based method to sort and separatecolloids in microfluidic channels.

Realizing single photon sources emitting in the telecom band on silicon substrates is essential to reach complementary-metal-oxide-semiconductor (CMOS) compatible devices that secure communications over long distances. In this work, we propose the monolithic growth of needlelike tapered InAs/InP quantum dot-nanowires (QD-NWs) on silicon substrates with a small taper angle and a nanowire diameter tailored to support a single mode waveguide. Such a NW geometry is obtained by a controlled balance over axial and radial growths during the gold-catalyzed growth of the NWs by molecular beam epitaxy. This allows us to investigate the impact of the taper angle on the emission properties of a single InAs/InP QD-NW. At room temperature, a Gaussian far-field emission profile in the telecom O-band with a beam divergence angle θ = 30° is demonstrated from a single InAs QD embedded in a 2° tapered InP NW. Moreover, single photon emission is observed at cryogenic temperature for an off-resonant excitation and the best result, g2(0) = 0.05, is obtained for a 7° tapered NW. This all-encompassing study paves the way for the monolithic growth on silicon of an efficient single photon source in the telecom band based on InAs/InP QD-NWs.

The temperature-dependence of the piezoelectric properties of trigonal -GeO2 single-crystals obtained by the high-temperature flux method was measured by the resonance technique of the electrical impedance in the 20°C-600°C range. To approach the values of the two independent piezoelectric coefficients d11 and d14, we first measured as a function of temperature the elastic coefficients S11, S14 and S66 and the dielectric permittivity 11 which are involved in the coupling coefficient k of both the thickness shear mode and the transverse mode. A Y-cut plate with a simple +45°-rotation ((YXtwl) +45°/0°/0°) was used to measure the coupling coefficient of the thickness shear mode, and two X-turned plates ((XYtwl) +45°/0°/0° and (XYtwl)-45°/0°/0°) were prepared to characterize the coupling coefficient of two transverse modes. From the whole experimental measurements, the piezoelectric coefficients of -GeO2 were calculated up to 600 °C. They show that this crystal is one of the most efficient in regard of the -quartz-like family at room temperature, and that its thermal comportment retains large piezoelectric properties up to 600°C.

Near-field radiative heat transfer exhibits various effects, such as amplification due to the geometry of the system. In this work, we construct a periodic layered structure which consists of multiple layers of alternating materials. Radiative heat transfer (RHT) between nanoparticles placed on each side of an intermediate structure is studied. Thermal energy exchange between nanoparticles is assisted by transmitted evanescent fields, which is theoretically included in the system's Green's function. We show that the resulting heat transfer with the assistance of a multilayered structure is more than five orders of magnitude higher than that in the absence of the multilayered structure at the same interparticle distance. This increase is observed over a broad range of distances ranging from near to far field. This is due to the fact that the intermediate multilayered structure supports hyperbolic phonon polaritons, where the edge frequencies of the type-I and type-II reststrahlen bands coincide at a value that is approximately equal to the nanoparticle resonance. This allows high-k evanescent modes to resonate with the nanoparticles. The effects of the number of layers and fill factor in the multilayered structure on RHT are examined. Finally, we show that when there is a lateral distance between the two particles assisted by the interference of surface waves, RHT conductance exhibits an oscillating and nonmonotonic behavior with respect to the lateral distance between nanoparticles. These results illustrate a powerful method for regulating energy transport in particle systems and can be relevant for effective energy management at nano-micro scales.

Secondary flows are ubiquitous in channel flows, where small velocity components perpendicular to the main velocity appear due to the complexity of the channel geometry and/or that of the flow itself such as from inertial or non-Newtonian effects, etc. We investigate here the inertialess secondary flow of viscoelastic fluids in curved microchan-nels of rectangular cross-section and constant but alternating curvature: the so-called "serpentine channel" geometry. Numerical calculations (Poole et al, 2013) have shown that in this geometry, in the absence of elastic instabilities, a steady secondary flow develops that takes the shape of two counter-rotating vortices in the plane of the channel cross-section. We present the first experimental visualization evidence and characterization of these steady secondary flows, using a complementarity of µPIV in the plane of the channel, and L. Ducloué · L. Casanellas · A. Lindner confocal visualisation of dye-stream transport in the cross-sectional plane. We show that the measured streamlines and the relative velocity magnitude of the secondary flows are in qualitative agreement with the numerical results. In addition to our techniques being broadly applicable to the character-isation of three-dimensional flow structures in microchan-nels, our results are important for understanding the onset of instability in serpentine viscoelastic flows.

Nanolaminate membranes made of two-dimensional materials such as graphene oxide are promising candidates for molecular sieving via size-limited diffusion in the two-dimensional capillaries, but high hydrophilicity makes these membranes unstable in water. Here, we report a nanolaminate membrane based on covalently functionalized molybdenum disulfide (MoS2) nanosheets. The functionalized MoS2 membranes demonstrate >90% and similar to 87% rejection for micropollutants and NaCl, respectively, when operating under reverse osmotic conditions. The sieving performance and water flux of the functionalized MoS2 membranes are attributed both to control of the capillary widths of the nanolaminates and to control of the surface chemistry of the nanosheets. We identify small hydrophobic functional groups, such as the methyl group, as the most promising for water purification. Methyl- functionalized nanosheets show high water permeation rates as confirmed by our molecular dynamic simulations, while maintaining high NaCl rejection. Control of the surface chemistry and the interlayer spacing therefore offers opportunities to tune the selectivity of the membranes while enhancing their stability