Chemical vapor deposition has proved to be successful in producing graphene samples on silicon carbide (SiC) homogeneous at the centimeter scale in terms of Hall conductance quantization. Here, we report on the realization of co-planar diffusive Al/ monolayer graphene/ Al junctions on the same graphene sheet, with separations between the electrodes down to 200 nm. Robust Josephson coupling has been measured for separations not larger than 300 nm. Transport properties are reproducible on different junctions and indicate that graphene on SiC substrates is a concrete candidate to provide scalability of hybrid Josephson graphene/superconductor devices.

Electrical transport (resistivity and Hall Effect) have been studied in silicon doped aluminum nitride (AlN) thick epitaxial layers from 250 K up to 1000 K. The investigated samples, grown by molecular beam epitaxy were characterized by n-type conduction with an ambient temperature free carrier concentration of about ~ 1 x 10^15 cm^3. The donor level, situated about 250 meV below the conduction band edge, was found to be responsible for the experimentally observed increase of free carrier concentration withtemperature. The temperature dependence of carrier mobility has been analyzed in the framework of a multimode scattering model. In the investigated samples the main scattering mechanism is supposed to be dislocation scattering.

Influence of AlN thickness on AlGaN epilayer grown by MOCVD

Electromagnetic coils are ubiquitously used in the modern world in motors, antennas, etc. In many applications (magnetic field coil calibration and nuclear magnetic resonance spectroscopy and imaging) there is a strong need for a homogeneous magnetic field. In this paper, we propose a simple modelling based on serial Fourier decomposition allowing the determination of the electrical conductor distribution to make the magnetic field homogeneous. The method is valid both for plane and axisymmetric geometries. The method allows the retrieval of the classical configurations of saddle coil for the plane geometry and Helmholtz coil for the axisymmetric one. The method is generalized for any number of electrical conductors and brings the perspective of new homogeneous magnetic resonance imaging (MRI) coil configuration.

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.

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.