GaAsO4 crystals were grown by a hydrothermal epitaxial process. Micro crystalline GaAsO4 powder was first synthesized by hydrothermal methods by using GaAs as a starting material in a sulfuric acid solvent under oxidizing conditions. Experimental conditions were optimized and the yield of the nutrient synthesis reached 88%. GaAsO4 powder was then used as the nutrient for growing GaAsO4 single crystals by epitaxy on (2(1) over bar 0) oriented GaPO4, AlPO4 and GaAsO4 plates. Crystal growth was performed in a horizontal PTFE-lined autoclave divided into two parts using sulfuric acid as the solvent under a slow heating gradient. Hydrothermal conditions were optimized in order to improve the crystal quality. The influence of the nature and orientation of the seeds on the growth rate was studied. From the solubility curve, the solute supply Delta S as a function of temperature during the growth process was calculated. Transparent crystals were obtained with Delta S between 0.002 and 0.009 mol/L. Large crystals (3.9 Chi 1.8 Chi 1.4 cm(3)) of gallium arsenate were obtained. These crystals were cut into (2(1) over bar 0), (010) and (001) plates. Mapping using Raman spectroscopy was performed in order to study the growth recovery on the seed. GaAsO4 crystals were characterized by infrared spectroscopy in order to quantify the amount of OH groups in the crystal structure. A low value of the absorption coefficient a at 3300 cm(-1) was measured 0.067 cm(-1) indicating a good crystal quality. Optical measurements were performed on GaAsO4 crystals by UV-vis-NIR spectrophotometry. Gallium arsenate exhibits the highest value of birefringence in the alpha-quartz group with Delta n =0.033. The transmission in the spectral region above 250 nm yields a bandgap of 5.85 eV. Piezoelectric properties were measured on resonators. An electromechanical coupling coefficient of 20% was measured which is the highest in the alpha-quartz group. A quality factor QF of 3.2 Chi 10(10) was obtained on a Y-cut plate. The C-66 elastic constant was found to be 20 GPa.

At low temperature the photoluminescence of single-wall carbon nanotubes show a large variety of spectral profiles ranging from ultra narrow lines in suspended nanotubes to broad and asymmetrical line-shapes that puzzle the current interpretation in terms of exciton-phonon coupling. Here, we present a complete set of photoluminescence profiles in matrix embedded nanotubes including unprecedented narrow emission lines. We demonstrate that the diversity of the low-temperature luminescence profiles in nanotubes originates in tiny modifications of their low-energy acoustic phonon modes. When low energy modes are locally suppressed, a sharp photoluminescence line as narrow as 0.7 meV is restored. Furthermore, multi-peak luminescence profiles with specific temperature dependence show the presence of confined phonon modes.

Nondestructive studies of physiological processes in agronomic products require increasingly higher spatial and temporal resolutions. Nuclear Magnetic Resonance (NMR) imaging is a non-invasive technique providing physiological and morphological information on biological tissues. The aim of this study was to design a robust and accurate quantitative measurement method based on NMR imaging combined with contrast agent (CA) for mapping and quantifying water transport in growing cherry tomato fruits. A multiple flip-angle Spoiled Gradient Echo (SGE) imaging sequence was used to evaluate the intrinsic parameters maps M0 and T1 of the fruit tissues. Water transport and paths flow were monitored using Gd3+/[Fe(CN)6]3−/D − mannitol nanoparticles as a tracer. This dynamic study was carried out using a compartmental modeling. The CA was preferentially accumulated in the surrounding tissues of columella and in the seed envelopes. The total quantities and the average volume flow of water estimated are: 198 mg, 1.76 mm3/h for the columella and 326 mg, 2.91 mm3/h for the seed envelopes. We demonstrate in this paper that the NMR imaging technique coupled with efficient and biocompatible CA in physiological medium has the potential to become a major tool in plant physiology research.

In this work we present an admittance study of a two-dimensional electron gas(2DEG) in thequantum Hall effect (QHE) regime. We have studied several Hall bars in different contacts configurations in the frequency range100Hz-1 MHz. Our interpretation is based on the Landauer-Büttiker theory and takes into account both the capacitance and the topology of the coaxial cables which are connected to the sample holder. We show that we always observe losses through the capacitive impedance of the coaxial cables, except in the two contacts configuration in which the cable capacitance does not influence the admittance measurement of the sample. In this case, we measure the electrochemical capacitance of the 2DEG and show its dependence with the filling factor ν.

We present an experimental study of the low frequency admittance of quantum Hall conductors in the [100 Hz, 1 MHz] frequency range. We show that the frequency dependence of the admittance of the sample strongly depends on the topology of the contacts connections. Our experimental results are well explained within the Christen and Büttiker approach for finite frequency transport in quantum Hall edge channels taking into account the influence of the coaxial cables capacitance. In the Hall bar geometry, we demonstrate that there exists a configuration in which the cable capacitance does not influence the admittance measurement of the sample. In this case, we measure the electrochemical capacitance of the sample and observe its dependence on the filling factor.

We present a general scheme to realize a cold-atom quantum simulator of bidimensional atomic crystals. Our model is based on the use of two independently trapped atomic species: the first one, subject to a strong in-plane confinement, constitutes a two-dimensional matter wave which interacts only with atoms of the second species, deeply trapped around the nodes of a two-dimensional optical lattice. By introducing a general analytic approach we show that the system Green function can be exactly determined, allowing for the investigation of the matter-wave transport properties. We propose some illustrative applications to both Bravais (square, triangular) and non-Bravais (graphene, kagomé) lattices, studying both ideal periodic systems and experimental-size and disordered ones. Some remarkable spectral properties of these atomic artificial lattices are pointed out, such as the emergence of single and multiple gaps, flat bands, and Dirac cones. All these features can be manipulated via the interspecies interaction, which proves to be widely tunable due to the interplay between scattering length and confinements.

We investigate electro-optical properties of suspensions of gold anisometric particles. Gold nanoparticles exhibit localized surface plasmon properties with a transverse mode and longitudinal mode in case of ellipsoidal shape. The transverse mode remains maximum in the visible range but the longitudinal one is red shifted and its resonance strongly depend on the aspect ratio of the nanoparticles. Among others, we thus expect highly tunable properties at optical frequencies under the external electric field. In our experimental setup, the electrodes are placed outside the sample. In this configuration, they do not interact with the suspension. We work with two kinds of particles: gold nanorods (GNRs) dispersed in water with an aspect ratio AR ≈10 (Φ=10nm) and gold nanowires (GNWs) dispersed in hexane with an AR≈1000 (Φ=1.5nm). We observed alignment of both GNRs and GNWs along the applied electric field due the intrinsic conductivity of the particles. Time responses of GNRs to the electric field are of the order of the millisecond and of more than 10 ms for GNWs. The saturated voltage is 4 times smaller in this last case compared to GNRs. Those results are in agreement with a change in the aspect ratio. More surprising, dichroism and spectroscopy measurements reveal, in both cases, a positive dichroism in the optical visible range. On the contrary, we expect a negative one (ie absorption higher for polarization perpendicular to the electric field) while in this frequency range, we are sensitive to the transverse mode of the plasmon band. This suggests that this mode is less sensitive to polarization than the longitudinal one . Concerning GNWs, a longitudinal plasmon band is not yet evidenced. To the best of our knowledge, numerical simulations have only predicted their presence for wire of similar length but larger diameter. Similarly to carbon nanotubes, we observe their progressive assembly into fibers strictly oriented along the electric field. Those fibers appear highly birefringent between crossed polarisers. Their properties and the way to control their growth are under investigation.