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Synthèse chimique et intégration de nanofils de ZnO pour le développement de nanogénérateurs piézoélectriques

Abstract : Piezoelectric nanogenerators arouse a particular interest for the supply of low power microsystems due to their great miniaturization capacity and high autonomy. The development of efficient devices from abundant and non-toxic materials and through low-cost processes represents however a prerequisite needed for their large-scale implementation, and remains a major technological challenge. In this context, the use of arrays of ZnO nanowires grown by chemical bath deposition within vertically integrated architectures is highly promising. To obtain efficient piezoelectric nanogenerators, a precise control of the morphological and electrical properties of these nanowires is required, while the use of metallic seed layers is favored for the nucleation of ZnO nanowires. Therefore, the main goal of this thesis is to address these issues through several complementary strategies.First, a particular effort was carried out to elucidate the nucleation mechanisms of the nanowires from gold seed layers. Two populations of nanowires with characteristic orientations were identified, each of them revealing a distinct nucleation mechanism. Furthermore, the influence of the microstructure of the gold seed layer and the properties of the chemical bath on the morphology of ZnO nanowires was thoroughly examined. A theoretical model describing predictively the elongation of ZnO nanowires in dynamic conditions was then established from Fick’s laws of diffusion, where two scenarios were taken into account depending on whether the growth reactor is considered of semi-infinite or of finite height. By comparing this model to experimental data, an activation energy for the crystallization of ZnO of 198 ± 24 kJ/mol was deduced, revealing the high interest of this model both for fundamental and applied researches. Copper was then considered as a doping element to enhance the electrical resistivity of ZnO nanowires by compensatory doping. In this purpose, the effects of the addition of Cu(NO3)2 during the growth of ZnO nanowires were studied at different pH values of the chemical bath. Complex incorporation mechanisms of copper into the ZnO lattice were revealed, which can be explained beyond the only considerations of electrostatic forces. Finally, the integration of these arrays of ZnO nanowires into piezoelectric nanogenerators was considered, where an analytical approach was developed to assess the electrical potential generated by a compressed nanowire. The possibility to strengthen the morphological control of ZnO nanowires through the realization of localized growth assisted by advanced lithography techniques was furthermore considered. Piezoelectric nanogenerators were eventually produced and characterized through the optimization of the fabrication process and the assembling of a whole piezoelectric measurement bench.
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Submitted on : Saturday, July 2, 2022 - 1:06:22 AM
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Clément Lausecker. Synthèse chimique et intégration de nanofils de ZnO pour le développement de nanogénérateurs piézoélectriques. Micro et nanotechnologies/Microélectronique. Université Grenoble Alpes [2020-..], 2021. Français. ⟨NNT : 2021GRALT052⟩. ⟨tel-03712017⟩

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