Publications: Articles

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

Mots clefs: Bismuth telluride Ionic liquid Electrodeposition Thermoelectricity

Resume: Abstract In this paper, we report the electrodeposition of stoichiometric Bi2Te3 compound using an ionic liquid binary mixture: 1-ethyl-1-octyl-piperidinium bis(trifluoromethylsulfonyl)imide: 1-ethyl-1-octyl-piperidinium bromide (EOPipTFSI:EOPipBr 95:5 (mol%)). The use of this mixture allows to reach a higher solubility of Bi(III) and Te(IV) precursors compared to pure EOPipTFSI ionic liquid in which Te(IV) salts are not soluble. Moreover, this electrolyte presents an extended cathodic stability, allowing the study of electrochemical processes that occur at high cathodic potential values. A detailed voltammetric study of electrochemical systems was performed for electrolytes containing different [Bi(III)]/[Te(IV)] ratio, allowing the attribution of cathodic signals to electrochemical processes. Experimental conditions leading to the deposition of stoichiometric Bi2Te3 were then determined by varying deposition potential and electrolyte composition, using potentiostatic experiments followed by XRD and SEM-EDX analysis. By varying the concentration of precursors in the electrolyte, mirror-like coatings, adherent and homogeneous, were obtained. Electroplated Bi2Te3 presents n-type conductivity with a Seebeck coefficient equal to ?70 ?V K?1 and an electrical resistivity of 133 ?? m.

Equipe: Département CP2S : Chimie et électrochimie des matériaux

Equipe: Département P2M : Surfaces et Spectroscopies

Equipe: Département SI2M : Microstructures et Contraintes

Equipe: Département P2M : Nanomagnétisme et Electronique de Spin