Description du sujet de thèse

Already around 15 years ago, it has been shown that liquid crystal topological defects can be used to confine and organize nanoparticles. In particular, oriented chains of nanospheres or of tip-to-tip nanorods have been formed in unidimensional smectic defects, dislocations and disclinations [1, 2]. The liquid crystal phase transitions occurring at low temperature, liquid crystals can provide temperature-activated assemblies of nanoparticles [3]. In this context, we propose to use oriented unidimensional smectic defects in order to build plasmonic cavities based on strictly facing gold (or silver/gold) nanorods or bipyramids in close contact. They will provide electromagnetic field enhancement in the cavity placed between the neighboring nanorods or bipyramids. We will study how to vary from weak to strong coupling between the plasmonic cavity and fluorophores specifically connected to the nanorods (or bipyramid) tips. A strong coupling regime for emitters located within all the cavities forming a chain confined within a defect will give access to cooperative coherent emission processes at room temperature such as superradiance and superfluorescence.
We will finally study the evolution of the coupling when temperature is increased in relation with the disappearing of the liquid crystal defects driven by the liquid crystal phase transition. This study will pave the way for an activation of the coupling strength between nanoparticles and fluorophores actively tuned by the temperature. This would be a first step towards optical devices based on strong or weak coupling between plasmonic cavities and fluorophores controlled by varying temperature.

[1] S.P. Do et al. Nano Letters 20 (2020) 1598, [2] B. Rozic, ACSNano 11 (2017) 6728 [3], H. Jeridi, Appl. Phys. Lett. 123 (2023) 203101

Contexte de travail

This thesis is funded by an ANR project involving three laboratories: the Institut des NanoSciences de Paris (INSP), the Institut de Chimie de la matière condensée de Bordeaux (ICMCB) and the Institut Langevin in Paris. The thesis will be carried out in close collaboration with these two last laboratories.
It will take place at the INSP, a joint research unit (UMR 7588) of the CNRS and Sorbonne University. This institute is directed by Massimiliano Marangolo, a professor at Sorbonne University, and its scientific objectives lie at the heart of fundamental nanoscience research. At INSP, the thesis will take place in the Physicochemistry and Surface Dynamics team on the Jussieu campus, in the group headed by Emmanuelle Lacaze, with 4 PhD students already in the group, 2 of whom are writing their thesis (at the end of their 3rd year).

Contraintes et risques

no constraints