Publications: Articles

Mots clefs: electrodeposition,thermoelectricity,microscale devices

Resume: Starting with the first published works on the electrochemical deposition of thermoelectric (TE) V–VI compounds in the early nineties, these past two decades have seen a steady increase in scientific interest and publications on this topic. This is hardly surprising, as TE devices offer unique opportunities for power generation in virtually any environment (“energy harvesting”) or demanding cooling applications through the Peltier effect. This review first provides an overview of the advances in the electrodeposition of n- and p-type thin films based on Bi2(Te, Se)3 and (Bi, Sb)2Te3, the currently best-known TE materials for room temperature applications. The overview includes information about the electrolyte and the deposition conditions as well as the achieved composition, thickness, morphology, and TE properties of the deposited films. Additionally, we present the state-of-the-art and recent developments in electroplating-based fabrication processes for microscale TE devices.

Equipe: Département CP2S : Chimie et électrochimie des matériaux

Resume: The electron temperature and electron density are measured in a microwave (MW) plasma-assisted chemical vapour diamond deposition reactor for different experimental conditions by varying the substrate temperature, methane content and MW power density. Optical emission spectroscopy (OES) and MW interferometry are used to probe the discharge generated in a stainless steel resonant cavity excited at a frequency of 2.45 GHz. Changing the substrate temperature from 630 to 900 ?C does not show any significant influence on the electron temperature or on the electron density. Increasing the methane content from 0 to 10% does not lead to any modification of the electron temperature or density. However between 10% and 20% CH, a decrease of the electron density is observed which may be attributed to soot particle formation. The electron density increases in the range of (1.2-10) x 1011 cm-3 from moderate power density conditions (50 hPa/1000 W) to high power density conditions (250 hPa/3500 W). OES measurements show that the electron temperature exhibits a flat axial profile in the plasma bulk and ranges from 14 000K at (25 hPa/600 W) to 10 500K at (400 hPa/3000 W).

Equipe: Département CP2S : Expériences et Simulations des Plasmas Réactifs - Interaction plasma-surface et Traitement des Surfaces ESPRITS

Equipe: Département P2M : Surfaces et Spectroscopies

Resume: In the framework of the new ecological regulations, micro-arc oxidation (MAO) appears as an alternativeto usual processes in the field of corrosion protection of Mg alloys. In this work, the initial stagesof anodic layer growth in KOH-based electrolytes are studied up to and beyond the initiation of themicro-arc regime.The properties of the first anodized film preceding the occurrence of the dielectric breakdown (corre-sponding to the start of the micro-arc regime) are mainly determined by the incorporation of additives(fluorides or silicates) in the film, as shown by in situ electrochemical measurements. Scanning electronmicroscopy (SEM), X-ray photoelectron spectroscopy (XPS) and micro-Raman spectroscopy reveal boththe change of morphology and chemical state of silicate and fluoride in the anodized layer before andafter the micro-arc regime. In terms of electrochemical behaviour, investigated by stationary methodsand electrochemical impedance spectroscopy (EIS) in reference corrosive water, the anodic film grownin the silicate medium provides the best corrosion resistance thanks to a thick layer containing Mg2SiO4,whose degradation products seal the porosities of the coating.

Equipe: Département CP2S : Expériences et Simulations des Plasmas Réactifs - Interaction plasma-surface et Traitement des Surfaces ESPRITS

Equipe: Département SI2M : Microstructures et Contraintes