Spin noise spectroscopy is a powerful technique for studying spin relaxation in semiconductors. Inthis article, we propose an extension of this technique based on optical heterodyne detection of spinnoise, which provides several key advantages compared to conventional spin noise spectroscopy:detection of high frequency spin noise not limited by detector bandwidth or sampling rates of digitizers,quantum limited sensitivity even in case of very weak probe power, and possible amplificationof the spin noise signal. Heterodyne detection of spin noise is demonstrated on insulating n-dopedGaAs. From measurements of spin noise spectra up to 0.4 Tesla, we determined the distribution ofg-factors, Δg/g = 0.49%.

Janus colloidal particles show remarkable properties in terms of surface activity, self-assembly and wetting. Moreover they can perform autonomous motion if they can chemically react with the liquid in which they are immersed. In order to understand the self-propelled motion of catalytic Janus colloids at the air-water interface, wetting and the orientation of the catalytic surface are important properties to be investigated. Wetting plays a central role in active motion since it determines the contact between fuel and catalytic surface as well as the efficiency of transduction of chemical reaction into motion. Active motion is not expected to occur either when the catalytic face is completely out of the aqueous phase or when the Janus boundaries are parallel to the interfacial plane. The design of a Janus colloid possessing two hydrophilic faces is required to allow the catalytic face to react with the fuel (e.g. H2O2 for Platinum) in water and to permit some rotational freedom of the Janus colloid in order to generate propulsion parallel to the interfacial plane.Here, we discuss some theoretical aspects that should be accounted when studying Janus colloids at the surface of water. The free energy of ideal Janus colloidal particles at the interface is modeled as a function of the immersion depth and the particle orientation. Analytical expressions of the energy profiles are established. Energetic aspects are then discussed in relation to the particle ability to rotate at the interface. By introducing contact angle hysteresis we describe how the effects of contact line pinning modifies the scenario described in the ideal case. Experimental observations of the contact angle hysteresis of Janus colloids at the interface reveal the effect of pinning; and orientations of silica particles half covered with a platinum layer at the interface do not comply with the ideal scenarios. Experimental observations suggest that Janus colloids at the fluid interface behave as kinetically driven system, where the contact line motion over defects decorating the Janus faces rules the orientation and rotational diffusion of the particle.

The interface between two fluids is never flat at the nanoscale, and this is important for transport across interfaces. In absence of any external field, the surface roughness is due to thermally excited capillary waves possessing subnanometric amplitudes in the case of simple liquids. Here, we investigate the effect of ultrasound on the surface roughness of liquid-gas and liquid-liquid interfaces. MHz frequency ultrasound was applied normal to the interface at relatively low ultrasonic pressures (< 0.6 MPa), and the amplitudes of surface fluctuations have been measured by light reflectivity and ellipsometry. We found a dramatic enhancement of surface roughness, roughly linear with intensity, with vertical displacements of the interface as high as 50-100 nm. As a consequence, the effective contact area between two fluids can be increased by ultrasound. This result has a clear impact for enhancing interface based processes such as mass or heat transfer.

Miniaturized total analysis systems are becoming a powerful tool for analytical and bioanalytical applications. Biological and chemical sensors for health and environment demand an adaptable technology [1]. A flexible and low-cost process using good quality material in terms of mechanical and thermal properties is necessary. Hybrid materials mixing organic and inorganic parts, offer the advantages of polymer-like materials and glasses. In this work, microfluidic sensor has been fabricated on a new hybrid organic-inorganic photosensitive material using an accurate and flexible fabrication process based on a pulsed UV laser lithography. The photosensitive material is based on, poly (amic acid) PAA polymer with lower molecular weight, 1,3,5-tris[2-vinyloxy)ethoxy]benzene TVEB as a crosslinking dissolution inhibitor, a VEPTES pre-hydrolysed as an organic-inorganic material, and a PAG as a photoacid generator. A fine positive pattern was fabricated in a 3 μm thick film with … mJ/cm2 of i-line exposure.This work presents the material synthesis, and the characterization of the mechanical and thermal properties. The nanoindentation technique was used to analyze the force required to indent the coating with a diamond tip. At low forces, this technique, based on indentation depth, predicts the hardness and the elastic modulus of the coating, to study the effect of the addition of the mineral part on the mechanical properties of the layer. On the other hand, thermogravimetric analysis (TGA) technique was used to study the thermal properties of the new hybrid material as function of inorganic part. These results indicate that the newly prepared photosensitive hybrid materials may have potential applications for microfluidic devices.

Nuclear Magnetic Resonance spectroscopy and imaging can be classified as inductive techniques working in the near- to far-field regimes. We investigate an alternative capacitive detection with the use of micrometer sized probes positioned at sub wavelength distances of the sample in order to characterize and model evanescent electromagnetic fields originating from NMR phenomenon. We report that in this experimental configuration the available NMR signal is one order of magnitude larger and follows an exponential decay inversely proportional to the size of the emitters. Those investigations open a new road to a better understanding of the evanescent waves component in NMR with the opportunity to perform localized spectroscopy and imaging.

Layered compounds are stacks of weakly bound two-dimensional atomic crystals, with a prototypal hexagonal structure in graphene, transition metal dichalcogenides and boron nitride. This crystalline anisotropy results in vibrational modes with specific symmetries depending on the in-plane or out-of- plane atomic displacements. We show that polarization-resolved photoluminescence measurements in hexagonal boron nitride reflect the phonon symmetries in this layered semiconductor. Experiments performed with a detection on the sample edge, perpendicular to the c-axis, reveal the strong polarization-dependence of the emission lines corresponding to the recombination assisted by the three acoustic phonon modes. We elucidate the dipole orientation of the fundamental indirect exciton. We demonstrate evidence of the so-far missing phonon replica due to the optical out-of- plane phonon mode.

Ce document présente une séance de travaux pratiques de caractérisation d'un magnétomètre à induction haute performance destinée aux étudiants de M2 OSAE de l'Observatoire de Meudon. Ce TP se déroule sur une journée et nécessite du matériel spécifique (bobines Helmholtz, analyseur de spectre).Le TP a pour but de comparer deux modes de fonctionnement du magnétomètre inductif permettant de s'affranchir de la résonance: la contre-réaction de flux et l'amplification en courant. Le TP permet de réaliser des caractérisations en champ magnétique et donner un cadre concret à des caractérisations de bruit.