Thèse soutenue

Ablation Laser de microparticules Terfenol-D (Tb0. 3Dy0. 7Fe1. 92) en aérosol. Dépôt supersonique de nanoparticules pour films magnétostrictifs épais

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Auteur / Autrice : Daniel O'Brien
Direction : Philippe Pernod
Type : Thèse de doctorat
Discipline(s) : Électronique
Date : Soutenance en 2006
Etablissement(s) : Ecole Centrale de Lille

Résumé

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This dissertation describes using microparticles of the (giant) magnetostrictive material Terfenol-D (Tb0. 3Dy0. 7Fe1. 92) in the Laser Ablation of Microparticle (LAM) aerosols process for the generation of nanoparticles and their subsequent supersonic impaction to form nanostructured magnetostrictive thick films. Solid Terfenol-D was ground to a powder having diameters from 0. 3 to 3 µm. This microparticle powder was then aerosolized and ablated by a KrF ultraviolet, pulsed laser in a continuously flowing aerosol process. The nanoparticles formed from the ablation were then accelerated through a supersonic nozzle into vacuum where they impacted onto a substrate at room temperature forming a film. The nanoparticles were amorphous, as shown by x-ray diffraction analysis of the deposited films and by Transmission Electron Microscopy of individual particles and had a size distribution typical of the LAM process : 3 to 20 nm in diameter with a mean size less than 10 nm. The deposited films were characterized using the cantilever method. Values of magnetostriction were on the order of 15 ppm for LAM deposited films. The observed reduced magnetostriction (1/30 that of comparable thin films) was due to oxidation, which source was identified by Spectroscopic analysis of the ablation plasma. Calculations showed that the extent of oxidation in the films was dependent on the microparticle feedstock size. For typical aerosol densities used in the LAM process, calculations showed that material made out of microparticules having a diameter larger than 3 µm was not significantly affected by background gas impurities or by an oxide shell.