Titre de la dissertation: Elaboration and Characterization of Hybrid Ferroelectric Nanocomposites using Advanced Scanning Probe Microscopy and Spectroscopy

Promoteur: Monsieur Philippe Leclère

Résumé de la dissertation: Ferroelectric and piezoelectric devices have seen a steady expansion in low-power electronic applications over recent years. However, their development increasingly relies on complex and heterogeneous material systems, for which reliable nanoscale characterization of electromechanical behaviour remains a major challenge. In particular, understanding how geometry, surface roughness, and multiphase interfaces influence the interpretation of Piezoresponse Force Microscopy (PFM) measurements is essential.

In this work, PVDF–TrFE/BiFeO₃ (BFO) thin film nanocomposites were selected as a model system and were elaborated by spin coating, enabling the production of uniform films compatible with SPM-based characterisation. BFO nanoparticles synthesised via a sol–gel route were embedded either in a conductive PEDOT:PSS matrix or directly within the ferroelectric polymer matrix.

A combination of structural, mechanical, and electrical characterisation techniques confirmed the phase purity, morphology, and electrical integrity of the samples. Conventional PFM revealed well-defined ferroelectric domains in PVDF–TrFE but proved unreliable for BFO-containing composites due to strong mechanical heterogeneity and pronounced surface roughness. Advanced PFM approaches, including dual-frequency resonance tracking (DFRT-PFM), switching-spectroscopy PFM combined with clustering analysis, and DataCube-PFM, were therefore exploited to improve measurement stability and to discriminate genuine ferroelectric responses from artefactual signals.

Switching-spectroscopy measurements demonstrated robust and reproducible ferroelectric switching in PVDF–TrFE, whereas BFO nanoparticles exhibited highly heterogeneous and environment-dependent behaviour. DataCube-PFM enabled spatially resolved reconstruction of apparent surface displacement while simultaneously accessing local mechanical properties.

Overall, this work establishes a robust methodological framework for a more reliable interpretation of PFM data in complex ferroelectric nanocomposite systems.