Thèse

Vendredi 6 Novembre 2026 à 14h00.

Ultrafast Thermal Transport and Acoustic Propagation across Carbon Nanotubes Interfaces and in Chalcogenide Thin Films

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Directeur de thèse / thesis director :
Paolo Maioli

Membres du jury / jury members :
Maria Cristina Larciprete
Pascal Ruello
Catherine Journet
Bruno Palpant

Résumé / Abstract :

The reduction of material dimensions to the nanoscale modifies energy transport mechanisms, increasing the influence of interfaces and confinement effects on thermal and acoustic properties. Understanding these processes is essential for the development of advanced functional materials, particularly for thermal management and energy conversion applications. Ultrafast optical spectroscopy was employed as a non-contact and non-destructive technique to investigate thermal transport across interfaces at the nanoscale and acoustic propagation in thin films, on femtosecond-to-nanosecond timescales.

A major part of this thesis focuses on interfacial heat transfer between optically excited carbon nanomaterials and their surrounding environment. This process is governed by the thermal boundary resistance (TBR), which quantifies the efficiency of heat transfer across the interface between a nanomaterial and a liquid or solid medium. Since TBR is strongly influenced by the chemical structure of the interface, particular attention was devoted to understanding the role of surface functionalization on thermal transport. Multi-wall carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) were synthesized and functionalized with hydroxyl, carboxyl, and amine groups. Their ultrafast thermal dynamics were investigated in both liquid suspensions and epoxy-based nanocomposites, providing quantitative measurements of the thermal coupling with the surrounding medium through the determination of TBR. The influence of both the nature and the degree of functionalization on interfacial heat transfer was systematically evaluated. The effective thermal and electrical conductivities of the resulting nanocomposites were measured and correlated with nanofiller concentration, thermal coupling with the matrix, and filler dispersion, the latter being assessed by optical and electron microscopy. These combined investigations establish a direct link between nanoscale interfacial heat transport, filler distribution within the matrix, and macroscopic transport properties.

In parallel, ultrafast thermal dynamics were investigated in single-wall carbon nanotubes (SWCNTs). The measurements revealed a characteristic transient optical response that differs significantly from that observed in MWCNTs. The transient optical response was found to be strongly dependent on the aggregation state of the nanotubes, revealing distinct dynamical signatures for isolated SWCNTs and rope-like bundles.

The thesis also addresses the acoustic and thermal properties of germanium telluride (GeTe), a chalcogenide material of interest for thermoelectric devices and phase-change memory technologies. Ultrafast optical spectroscopy was used to investigate hypersonic acoustic propagation in GeTe thin films in the 10–20 GHz frequency range. By analyzing the transient optical response of films with different thicknesses, it was possible to determine the longitudinal sound velocity and the intrinsic acoustic attenuation. Furthermore, the contribution of interface-related losses was separated from intrinsic propagation losses, providing a comprehensive characterization of acoustic transport in GeTe thin films.

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