Caractérisation de couches épaisses de semi-conducteur WO3 et WO3 / TiO2 pour la réalisation de capteurs à NO2

Les capteurs de mesure en continu de la concentration d'une espèce chimique dans un mélange gazeux connaissent un développement important, plus particulièrement lié au contrôle des combustions avec la double motivation d'économie d'énergie et de réduction de la pollution atmosphérique. De nombreux capteurs de composition des gaz concernent des molécules produites lors de l'oxydation des combustibles fossiles : O2, CO, CO2, H2O, SO2, SO3, Nox, CHx,... Dans le but de réaliser des capteurs pour contrôler la teneur en NO2 des gaz d'échappement, au niveau du pot catalytique, nous avons décidé d'aborder l'étude des matériaux de base servant à cet effet : couches épaisses à base de WO3 et WO3/TiO2 de 100 à 200 micromètres d'épaisseur. La forme, la composition et la géométrie du capteur varient avec différents paramètres, et en particulier avec le procédé d'élaboration de la partie sensible de celui-ci. L'analyse de tous les résultats obtenus nous a permis d'appréhender le comportement des couches (WO3, WO3/TiO2) du capteur, sous leur aspect général et surtout sous l'aspect comportement propre du matériau d'une part, d'autre part d'appréhender leur comportement vis-à-vis du gaz à détecter(NO2). L'étude thermique et spectroscopique nous a permis de mettre en évidence l'importance de l'effet de l'addition de TiO2 et de proposer une microstructure de la formation de ces couches. En effet, la couche est formée de grains polycristallins et homogènes de WO3, dans laquelle s'incrustent des grains de TiO2 en formant des liaisons intra-granulaires au niveau de l'interface. De ce fait, le TiO2 joue le rôle de stabilisateur et augmente la sensibilité de la couche vis-à-vis du gaz à détecter.Currently, the development of the chemical sensors applied in particular in the automobile industry to control the combustion process, becomes more and more important for economic reasons and to abate the atmospheric pollution. Several sensors are applied to detect different gas molecules produced or consumed during the oxidation of the combustibles materials like: O2, CO, CO2, H2O, SO2, SO3, Nox, CHx, etc. In order to realise the sensors controlling the volume of NO2 of the exhaust fumes in the exhaust pipe, we decided to study and characterise the basic materials used for this purpose, namely: WO3 and WO3/TiO2 thick layers with a thickness of 100-200 micrometers. The morphology, composition and the size of the sensor, from the viewpoint of its application, vary with different parameters, particularly with the variation of the elaboration conditions of the gas sensitive layer. The correlation between the experimental results allows us to understand the general behaviour of the WO3 and WO3/TiO2 thick layers from the aspect of the interaction of the two material types (WO3 and TiO2) on the one hand, and on other hand the sensing behaviour of these sensors in the presence of NO2. The spectroscopic and thermal studies allow us to recognise the importance of the TiO2 addition for the sensitivity of WO3 to NO2 and its stabilisation effect for the structure of the tungsten trioxide. On the basis of these results, we propose a microstructure for these mixed layers. Indeed, the layers are composed of polycristallin grains of WO3 interacting with the TiO2 grains forming chemical bonds at the domain of the interface. In this case, the addition of TiO2 leads to the structural stabilisation of the WO3 and increases the sensitivity of the layer for NO2.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceF

Electrical behaviour of hydridofluorides of potassium-calcium KCaH3-xFx with x = 1, 1.5, 2, 2.5

International audienceThis paper reports the results of the electrical conductivity measurements for KCaH3-xFx series with (x = 1, 1.5, 2, 2.5) in the temperature range 298-503 K. The activation energy of the electrical conductivity for the studied compounds depends on hydrogen amount and Reau's criteria. Differential thermal analysis curves were measured in the same temperature range 298-503 K. Possible correspondence between preferential order given by X-ray diffraction, thermal behaviour and electrical properties are discussed

Epitaxial Layer Parameters Estimation Approach of Silicon Carbide Schottky Diodes

International audienceSilicon-carbide Schottky diode is seen as one of the newest devices deployed in sensor application. Temperature sensors using these highly developed devices have been introduced. The linearity of the output signal versus temperature of the silicon-carbide Schottky diode is demonstrated. From a modeling point of view, accurate simulations are necessary for checking sensor behavior. These simulations tend to rely on component models and associated confidential epitaxial parameters. Therefore, this paper sets out to extract accurate parameters of the silicon-carbide Schottky diode. In pursuit of this end, a systematic approach is developed and a physically based model is introduced. This model is run for many devices, giving directly epitaxial layer parameters. A contrastive study between experimental and simulation is undertaken, resulting in good agreement

Enhancement of dielectric, piezoelectric, ferroelectric, and electrocaloric properties in slightly doped (Na 0.5 Bi 0.5 ) 0.94 Ba 0.06 TiO 3 ceramic by samarium

International audienceWe investigated the structural, dielectric, piezoelectric, ferroelectric, and electrocaloric properties of the samarium doped (Na0.5Bi0.5)(0.94)Ba0.06TiO3 (NBT-6BT) ceramic. X-ray diffraction and Raman spectra confirm the coexistence of the rhombohedral and tetragonal structures for a low amount of Sm (<= 8 mol. %), while the compositions with a higher amount of Sm2O3 (11 mol. %) have a pseudocubic structure. The thermal dependency of the dielectric permittivity revealed two phase transitions from ferroelectric to antiferroelectric at low temperatures, then to paraelectric phase at higher temperatures. The substitution of NBT-6BT with 2 mol. % of Sm2O3 remarkably enhances the ferroelectric and the piezoelectric properties of the (Na0.5Bi0.5)(0.94)Ba0.06TiO3 ceramic. Furthermore, a large electrocaloric effect (Delta T = 1.4K) was directly measured on the ceramic doped with 2 mol. % of Sm2O3 under an applied electric field of 50 kV/cm. Published under license by AIP Publishing

Etude des spectres vibrationnels et des proprietes electriques des hexahydrioaluminates alcalins Li3AlHnD6-n(n = 0-&gt;6) et Na3AlH6

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

The origin of the large magnetoelectric coupling in the ceramic Ba 0.1 Bi 0.9 (Ti 0.9 Zr 0.1 ) 0.1 Fe 0.9 O 3

International audienceAbstract 57 Fe Mössbauer spectrometry and x-ray powder diffraction are conducted to examine the structure and the local magnetic order at the level of Fe sites of Ba 0.1 Bi 0.9 (Ti 0.9 Zr 0.1 ) 0.1 Fe 0.9 O 3 ceramic. The Mössbauer spectra in the temperature range of 77 K–623 K were analyzed using a discrete distribution of hyperfine field, indicating that the Néel temperature T N was about 603 K. The ceramic Ba 0.1 Bi 0.9 (Ti 0.9 Zr 0.1 ) 0.1 Fe 0.9 O 3 remains stable in the rhombohedral structure ( R 3 c ) in the temperature range of 300 K–800 K. The anomaly of volume below T N , as detected from the model Debye–Gruneissen, reveals the presence of magnetoelastic coupling in this compound. The total polarization ( P ) obtained from Rietveld refined atomic positions is found to depend on the magnetic order that leads to the decrease of the total polarization ( P ) through the anomaly volume. The reduction in the polarization by Δ P ∼ −2.4 μ C cm −2 suggests negative magnetoelectric interaction. The total polarization ( P ) obtained from Rietveld refined atomic is coupled with the magnetic ordering mediated by magnetoelastic coupling. The hyperfine field ( B hf ) dependence of polarization ( P ) at a temperature range below T N exhibits a linear evolution, confirming the linear magnetoelectric coupling. At room temperature, the linear magnetoelectric coefficient is about α ME ≈ 1.84 × 10 −9 s m −1

Sensitivity Improvement of an Impedimetric Immunosensor Using Functionalized Iron Oxide Nanoparticles

This work has explored the development of impedimetric immunosensors based on magnetic iron nanoparticles (IrNP) functionalized with streptavidin to which a biotinylated FAB part of the antibody has been bound using a biotin-streptavidin interaction. SPR analysis shows a deviation on the measured (angle) during antigen-antibody recognition whereas label free detection using by EIS allows us to monitor variation of polarization resistance. Before detection, layers were analyzed by FTIR and AFM. Compared to immobilization of antibody on bare gold surface using aminodecanethiol SAM, antibody immobilization on nanoparticles permitted to reach lower detection limit: 500 pg/ml instead of 1 ng/ml to in the case of EIS and 300 ng/ml instead of 4.5 μg/ml in the case of SPR. Thus, it permitted to improve the sensitivity: from 257.3  Ω⋅cm2⋅μg−1⋅ml to 1871 Ω⋅cm2⋅μg−1⋅ml in the case of EIS and from 0.003°μg−1⋅ml to 0.094°μg−1⋅ml in the case of SPR

Analysis of micro power generator autonomous PZT with use of sliding mode control

International audienceResearch on energy harvesting and related technologies have attracted attention and have shown their potential in a wide range of applications, the portable electronic devices (numerical telephones, diaries, microcomputers, watches, medical prostheses...) accompany us, often in a banal way, in the everyday life; they render very many services to us but, because of their insufficient autonomy, also force us in our desires of mobility and autonomy. Many mechanisms of energy conversion and device designs for vibration-based energy harvesting have been developed and reported in literature, In addition to electromagnetic and electrostatic mechanisms that have been widely applied, many other mechanisms such as electrostrictive and dielectric polymers have also been investigated. The power optimality performance of a piezoelectric energy harvester connected to a resistive load is studied. An analytical solution for the piezoelectric energy harvester based on the piezoelectric constitutive equations and the fundamental mechanics of materials relations is adapted to estimate the optimal power and vibration amplitude. The influence of geometrical parameter on the stack piezoelectric is also investigated. The power harvesting in a pressure-loaded plate depends on several factors. The dominant parameters that affect the performance are the ratio of thickness layer and the area of electrode, a designated power management module for sub mW energy harvester is proposed in this article to increase the energy conversion efficiency and extend the energy storage Life time for small input power, with use sliding mode control The specimen was simulate under tow values ratio of thickness layer and the area 1/0.09 and 0.1/0.01. The measured output voltages for two different ration is 8V and The results indicate that the electricity power output has 2.2 mW