Defense of doctoral thesis of LOPEZ GARCIA Andres Jenaro for the University Grenoble Alpes, speciality " NANO ELECTRONIC & NANOTECHNOLOGIES ", entitled:
M256 Room PHELMA / MINATEC
3 rue Parvis Louis Néel 38016 GRENOBLE Cedex 1
Contribution to the study of the piezoelectric properties of ZnO nanowires and associated nanocomposites for application to mechanical-electrical energy transduction
Andres Jenaro LOPEZ GARCIA
Friday, June 3, 2022 at 2pm
Surface traps,traps dynamics,finite element model,piezoelectric sensor,mechanical energy harvesting
With the increasing development of wireless networks of low-power sensors for the so-called internet-of-things, there is a need for efficient ways to ensure the energetic autonomy of sensing nodes. Among the various energy harvesting solutions, converting the abundant mechanical energy present in the environment into electrical energy is very promising. In this emerging field of research, ZnO nanowires (NWs) have been strongly studied during these last two decades, both as such, and integrated into nanocomposite materials. At the nanoscale, they feature improved electromechanical properties compared to bulk, as well as easy integration and manufacturing, on both rigid and flexibles substrates. However, some intriguing discrepancies between the experimental and simulation results available at the beginning of this PhD highlighted the need for a better understanding of the piezoelectric operation of NW-based composites, especially for what concerns two important aspects which had been poorly addressed so far: the coupling between piezoelectric and semi-conducting properties in simulations, and the dependence of electromechanical properties with ZnO NW growth method or with NW surrounding environment in experiments.
From the theoretical point of view, this Ph.D. thesis studies the coupling of piezoelectric and semiconducting properties in ZnO NWs and related nanocomposites and provides optimization guidelines for mechanical to electrical transducing applications. It investigates the influence of doping level, free carrier density, interface traps and geometrical parameters on electromechanical parameters. Simulations of ZnO NW-based nanocomposites under mechanical compression were performed using the Finite Element Method (FEM). Experimentally, several atomic force microscopy (AFM) modes, such as piezoelectric force microscopy (PFM), Kelvin probe force microscopy (KPFM), and conducting atomic force microscopy (C-AFM) were used, in order to probe locally electrical and electromechanical parameters which play a key role in the efficiency of the piezoelectric response of ZnO NWs. Our results showed that doping level, free carriers and surface traps, as well as traps dynamics, must be considered in order to explain the amplitude and the potential asymmetry of the electromechanical response, or the influence that geometry has on it. They demonstrate that semiconducting properties should be taken into account for the analysis of experimental results and for the correct design of electromechanical self-powered devices based on ZnO NWs and nanocomposites.
Jury members :
Mireille MOUIS, RESEARCH DIRECTOR - CNRS DELEGATION ALPS : Supervisor
Oliver THOMAS, PROFESSOR of UNIVERSITIES - University Aix-Marseille : Reviewer
Noëlle GOGNEAU, RESEARCH DIRECTOR - CNRS DELEGATION ILE-DE-FRANCE SOUTH : Reviewer
Guylaine POULIN-VITTRANT, RESEARCH DIRECTOR - CNRS CENTRE LIMOUSIN POITOU-CHARENTES : Examiner
Alain SYLVESTRE, PROFESSOR of UNIVERSITIES - GRENOBLE INP : Examiner
Gustavo ARDILA RODRIGUEZ , ASSOCIATE PROFESSOR HDR - University Grenoble Alps : CoSupervisor
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Thesis prepared in the laboratory IMEP-LaHC (Institut de Microélectronique, Electromagnétisme et Photonique - Laboratoire d'Hyperfréquences et de Caractérisation) supervised by Mireille MOUIS , supervisor & Gustavo ARDILA RODRIGUEZ, Co-supervisor.