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11.
The glass—forming regions in the quaternary system GeSbTeSe have been obtained for quenching in air and for a constant cooling rate of 5°C min?1. The boundaries of the glass-forming regions and the thermal behaviour of the samples have been deduced from differential thermal analysis and X-ray diffraction. The results may be compared with some limited determinations of glass-forming ability in TeSe, GeTe, GeTeSe and GeSbSe systems, allowing for the fact that in the present work the experimental parameters for preparing and quenching the melts are identical for all the compositions studied. The formation and stability of glasses is discussed in terms of the obtained glass-forming regions and the observed thermal behaviour in differential thermal analysis measurements. Potential-device quality memory and switching compositions are suggested. 相似文献
12.
Calorimetric studies of the ferromagnetic Curie temperature Tc, and the crystallization kinetics of the metallic glass Fe78B9Si13 have been performed in an attempt to elucidate the possibility of reversible relaxation processes near Tc and the crystallization mechanisms taking place. From the change of Tc with heating rate and on annealing it appears that ageing irreversibly increases the Curie temperature. Crystallization is thermally activated following an Arrhenius behaviour and proceeds in two stages, the best fit to the experimental data for each stage of crystallization has been obtained by use of a Johnson-Mehl-Avrami-Erofe'ev equation. The effective activation energy and the kinetic exponent are respectively E = (4.7 ± 0.1) eV, n = 2.0 ± 0.2 for the first and E = (4.5 ± 0.1) eV, n = 4.0 ± 0.2 for the second stage of crystallization. From these results it appears that the mechanisms of crystallization are quite different in both stages. 相似文献
13.
Simon Clavaguera Olivier J. Dautel Lionel Hairault Christophe Méthivier Pierre Montméat Eric Pasquinet Claire‐Marie Pradier Françoise Serein‐Spirau Salem Wakim Florian Veignal Joël J. E. Moreau Jean‐Pierre Lère‐Porte 《Journal of polymer science. Part A, Polymer chemistry》2009,47(16):4141-4149
The detection of 2,4‐dinitrotoluene (DNT) by fluorescence quenching of a new class of polyimines consisting in π‐conjugated segments regularly alternated with chiral C2 symmetry units has been studied for solutions and thin films. Their photophysical properties and their sensitivity towards DNT detection has been compared to those of a small model molecule incorporating the same π‐conjugated segment. In solution, all the compounds exhibit the same photo‐physical properties and sensitivity towards DNT detection. In contrast, for thin films, better performances are observed in static conditions for this new class of polyimines compared to the small model molecule. It seems that C2 symmetry units prevent from the stacking of the π‐conjugated segments and provide in addition to high fluorescence signal an improved diffusion of the analyte inside the films. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4141–4149, 2009 相似文献
14.
Maria-Teresa?Clavaguera-MoraEmail author Narcís?Clavaguera Javier?Rodríguez-Viejo 《Monatshefte für Chemie / Chemical Monthly》2005,136(11):1947-1953
Summary. The primary crystallization of molten alloy systems at high undercooling is studied by a precise quantitative analysis of
the calorimetric signal obtained during the transformation in terms of the reaction rate under isothermal and continuous heating
regimes. It is shown that, under specific conditions, namely, stoechiometric primary precipitates, generalized relationships
for the crystallization enthalpy and the reaction rate may be obtained. 相似文献
15.
Efficient Sensing of Explosives by Using Fluorescent Nonporous Films of Oligophenyleneethynylene Derivatives Thanks to Optimal Structure Orientation and Exciton Migration
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Dr. Thomas Caron Dr. Eric Pasquinet Dr. Arie van der Lee Dr. Robert B. Pansu Dr. Vincent Rouessac Dr. Simon Clavaguera Dr. Myriam Bouhadid Prof. Françoise Serein‐Spirau Prof. Jean‐Pierre Lère‐Porte Dr. Pierre Montméat 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(46):15069-15076
The fluorescence of thin films of a diimine‐substituted phenyleneethynylene compound can be efficiently quenched by nitroaromatic vapors, which is not the case for the unsubstituted parent compound. Thin‐film porosity is usually considered to be an essential factor for efficient quenching, but in the present case the origin of the quenching is completely different, as both films are nonporous and hermetic to 2,4‐dinitrotoluene (DNT) molecules. The molecular organization in the two crystallized thin films offers a low level of π stacking for both compounds, but the orientation of the phenylenethynylene fluorophore differs markedly with respect to the surface of the films. For the substituted compound, the fluorophore is almost parallel to the surface, thus making it readily available to molecules of a nitroaromatic quencher. This rationale is also observed in the case of a related compound bearing methoxy side chains instead of the long octyloxy moieties. Fluorescence‐lifetime experiments show that the efficient quenching process in the nonporous crystallized films of the substituted compound is due to a fast (<70 ps) diffusion of excitons from the bulk of the film toward the surface where they are quenched, thus providing evidence of antenna effects. 相似文献
16.
17.
M.T. Clavaguera 《Journal of Physics and Chemistry of Solids》1975,36(11):1205-1211
We have measured the effect of uniaxial stress along the (100), (101), (110) and (001) crystallographic directions and of hydrostatic pressure on the resistivity in several single crystal samples of Cd3As2 with carrier concentration n ? 2 × 1018cm?3 at room temperature. The results are interpreted considering a multi-valley model for the conduction band. With the aid of group theoretical investigation we conclude that the non-equivalent valleys are located at the points Γ and Δ in the Brillouin Zone. 相似文献
18.
Delalande M Clavaguera S Toure M Carella A Lenfant S Deresmes D Vuillaume D Simonato JP 《Chemical communications (Cambridge, England)》2011,47(21):6048-6050
An innovative sensor for the detection of nerve agents in the gas phase based on a carbon nanotube field-effect transistor was developed. A high sensitivity to organophosphorus gases was obtained by modifying gold electrodes with specific tailor-made self-assembled monolayers. 相似文献
19.
The glass-forming ability of a Se0.615Ge0.154Sb0.231 alloy is analysed by computing the critical cooling rate and the time-temperature-transformation curve, at various temperatures. The calculation is based on some experimentally determined portions of the time-temperature-transformation curve, from which the rate of increase of viscosity with falling temperature below the melting point is deduced, using classical crystallization kinetics treatment. 相似文献
20.
Suńol J. J. Clavaguera-Mora M. T. Clavaguera N. 《Journal of Thermal Analysis and Calorimetry》2003,72(1):347-353
The crystallization kinetics of a melt spun Fe-Ni based alloy has been investigated, with both isothermal and continuous heating
experiments, by means of differential scanning calorimetry. The alloy presents two separated crystallization processes. In
order to perform the kinetic analysis of a melt spun metallic glass and to decide which kinetic model agrees better with the
experimental crystallization data as the crystallized fraction x. We compare the experimental dependence of ln(k0f(x)) vs. (1-x) and that predicted, assuming different model equations for f(x). Both crystallization processes follow the JMAE equation and the master curve is the same for isothermal and non-isothermal
data.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献