Structure of CdTe/ZnTe superlattices

The structure of CdTe/ZnTe superlattices has been analyzed through θ/2θ x‐ray diffraction, photoluminescence, and in situ reflection high‐energy electron diffraction (RHEED) measurements. Samples are found to break away from Cd_(x)Zn_(1−x)Te buffer layers as a consequence of the 6% lattice mismatch in this system. However, defect densities in these superlattices are seen to drop dramatically away from the buffer layer interface, accounting for the intense photoluminescence and high‐average strain fields seen in each of our samples. Observed variations in residual strains suggest that growth conditions play a role in forming misfit defects. This could explain discrepancies with calculated values of critical thickness based on models which neglect growth conditions. Photoluminescence spectra reveal that layer‐to‐layer growth proceeded with single monolayer uniformity, suggesting highly reproducible growth. Our results give hope for relatively defect‐free Cd_(x)Zn_(1−x)Te/Cd_(y)Zn_(1−y)Te superlattices with the potential for applications to optoelectronics offered by intense visible light emitters

Facile synthesis and optical properties of extended TPA-Benzodifuran derivatives connected by cyano-vinylene junctions

Two new conjugated molecules based on triphenylamine – benzo[1,2-b:4,5-b’]difuran moieties and integrating cyanovinyl bonds have been synthesized by using the new benzodifuran-acetonitrile synthon, easily and rapidly prepared in two steps from 2,2’-(2,5-dihydroxy-1,4-phenylene)diacetic acid. The electronic properties of the molecules were analysed by UV-Vis absorption and emission spectroscopies and cyclic voltammetry. The potential use of the molecules as donor materials for photovoltaic conversion were evaluated in simple bilayer solar cells using C60 as the acceptor materials. The comparison between the two derivatives reveals that the extension of the conjugated system with the insertion of furan cycles leads to a narrowing band gap, a better emission property, a direct access to dication state and an enhancement of the photovoltaic characteristics

Electrical determination of the valence-band discontinuity in HgTe-CdTe heterojunctions

Current-voltage behavior is studied experimentally in a Hg0.78Cd0.22Te-CdTe-Hg0.78Cd0.22Te heterostructure grown by molecular beam epitaxy. At temperatures above 160 K, energy-band diagrams suggest that the dominant low-bias current is thermionic hole emission across the CdTe barrier layer. This interpretation yields a direct determination of 390±75 meV for the HgTe-CdTe valence-band discontinuity at 300 K. Similar analyses of current-voltage data taken at 190–300 K suggest that the valence-band offset decreases at low temperatures in this heterojunction

Voltage controlled terahertz transmission through GaN quantum wells

We report measurements of radiation transmission in the 0.220--0.325 THz frequency domain through GaN quantum wells grown on sapphire substrates at room and low temperatures. A significant enhancement of the transmitted beam intensity with the applied voltage on the devices under test is found. For a deeper understanding of the physical phenomena involved, these results are compared with a phenomenological theory of light transmission under electric bias relating the transmission enhancement to changes in the differential mobility of the two-dimensional electron gas

Rational Topological Design for Fluorescence Enhancement upon Aggregation of Distyrylfuran Derivatives

A series of 2,5-distyrylfuran derivatives bearing pentafluorophenyl- and cyanovinyl units have been synthesized for aggregation-induced emission (AIE). The effect of the type and extent of the supramolecular connections on the AIE of the furan derivatives were examined and correlated with their X-ray crystal structures. It was found that the simultaneous presence of cyano and perfluorophenyl units strongly enhances the fluorescence upon aggregation. Single-crystal X-ray diffraction analysis confirmed that C — H⋅⋅⋅F, F⋅⋅⋅F, C — H⋅⋅⋅nitrile, Ar⋅⋅⋅ArF (Ar=aryl, ArF=fluoroaryl), and nitrile⋅⋅⋅ArF intra- and intermolecular interactions drive the topology of the molecule and that solid-state supramolecular contacts favor AIE of the furan derivatives

Structural and magnetic properties of Co2MnSi thin films

Co2MnSi (CMS) films of different thicknesses (20, 50, and 100 nm) were grown by radio frequency (RF) sputtering on a-plane sapphire substrates. Our X-rays diffraction (XRD) study shows that, in all the samples, the cubic 〈110〉 CMS axis is normal to the substrate and that six well defined preferential in-plane orientations are present. Static and dynamic magnetic properties were investigated using vibrating sample magnetometry (VSM) and microstrip line ferromagnetic resonance (MS-FMR), respectively. From the resonance measurements versus the direction and the amplitude of an applied magnetic field, most of the magnetic parameters are derived, i.e.: the magnetization, the gyromagnetic factor, the exchange stiffness coefficient, and the magnetic anisotropy terms. The in-plane anisotropy results from the superposition of two terms showing a twofold and a fourfold symmetry, respectively. The observed behavior of the hysteresis loops is in agreement with this complex form of the in-plane anisotropy.International audienceCo2MnSi (CMS) films of different thicknesses (20, 50, and 100 nm) were grown by radio frequency (RF) sputtering on a-plane sapphire substrates. Our X-rays diffraction (XRD) study shows that, in all the samples, the cubic 〈110〉 CMS axis is normal to the substrate and that six well defined preferential in-plane orientations are present. Static and dynamic magnetic properties were investigated using vibrating sample magnetometry (VSM) and microstrip line ferromagnetic resonance (MS-FMR), respectively. From the resonance measurements versus the direction and the amplitude of an applied magnetic field, most of the magnetic parameters are derived, i.e.: the magnetization, the gyromagnetic factor, the exchange stiffness coefficient, and the magnetic anisotropy terms. The in-plane anisotropy results from the superposition of two terms showing a twofold and a fourfold symmetry, respectively. The observed behavior of the hysteresis loops is in agreement with this complex form of the in-plane anisotropy

Distyrylfuranes: Synthesis and optical properties

Date du colloque : 05/2013</p

Synthèse verte de systèmes conjugués linéaires pour l&#039;électronique organique

Date du colloque : 10/2013National audienc

Synchrotron X-ray diffraction experiments with a prototype hybrid pixel detector

International audienceA prototype X-ray pixel area detector (XPAD3.1) has been used for X-ray diffraction experiments with synchrotron radiation. The characteristics of this detector are very attractive in terms of fast readout time, high dynamic range and high signal-to-noise ratio. The prototype XPAD3.1 enabled various diffraction experiments to be performed at different energies, sample-to-detector distances and detector angles with respect to the direct beam, yet it was necessary to perform corrections on the diffraction images according to the type of experiment. This paper is focused on calibration and correction procedures to obtain high-quality scientific results specifically developed in the context of three different experiments, namely mechanical characterization of nanostructured multilayers, elastic-plastic deformation of duplex steel and growth of carbon nanotubes