Description du sujet de thèse

Localized Surface Plasmon Resonances (LSPR) result from the collective oscillations of free carriers at metal–dielectric interfaces. They enable fine-tuned modulation of light/matter interactions, with major applications in fields such as optics, sensing, enhanced spectroscopy, and photovoltaics. When these resonances occur on nanometric-sized objects, quantum effects emerge, giving rise to the emerging field of quantum plasmonics, where collective and individual excitations of carriers coexist. This PhD is part of the ANR DIAAPASON project (Doped Semiconductor Nanostructures Quantum Plasmonics), which aims to explore the boundary between classical and quantum plasmonics in doped silicon nanostructures. In these semiconductor materials, the free carrier concentration is lower than in metals and can be tuned via doping. The plasmon frequency can thus be freely modulated in the infrared range, offering an additional degree of freedom and extending plasmonics into this spectral domain. Aside from a few theoretical works, no experimental study of quantum effects in plasmonics in doped semiconductor nanostructures has been conducted to date.

The objectives of this PhD will first involve fabricating model systems composed of assemblies of silicon nanodisks (SiNDs) with controlled size and doping. The student will be responsible for the fabrication of SiNDs through top-down processes using doped Silicon-On-Insulator (SOI) substrates. These substrates will be nanostructured by combining electron beam lithography and etching, in order to support plasmon resonances with anisotropic quantum confinement. The student will participate in the structural study of the doped SiNDs, which will be examined using High Resolution Transmission Electron Microscopy (TEM) and analytical spectroscopy (STEM-EDX, STEM-EELS) for chemical mapping of dopants inside individual SiNDs.

The candidate will also be in charge of studying the optical properties of these small plasmonic antenna assemblies using infrared spectroscopy. In order to probe the effect of different parameters (size, shape, doping, distance between SiNDs) on the plasmonic resonance, these experimental measurements will be combined with electromagnetic simulations based on the Finite Difference Time Domain (FDTD) method. These models will be complemented by atomistic simulations performed by a DIAAPASON project partner, allowing explicit descriptions of the dopants and their electronic structures. This combination of cutting-edge fabrication methods, advanced optical measurements, and both optical and atomistic simulations will allow investigation of the impact of size reduction and the few-electron regime on the plasmonic properties of these doped semiconductor nanostructures.

In addition to exploring the boundary between classical and quantum plasmonics, this PhD will also investigate a new class of plasmonic antennas based on the collective motion of free hole density — charge carriers that, like electrons, can exist in semiconductors. This new type of plasmonic antenna will be obtained by replacing phosphorus dopants (n-type doping) with boron atoms (p-type doping). For the latter, Raman spectroscopy will be used both to detect the incorporation of dopants via Fano resonances, and to probe the doping profiles at the nanometric scale using high-frequency acoustic phonons, which will act here as internal probes.

These new plasmonic antennas with ultimate dimensions pave the way for the realization of quantum-controlled devices such as single-photon sources or transistors, fully compatible with microelectronics technology.
Candidates should have a solid background in condensed matter physics and optics. Knowledge of the Python programming language will be appreciated.

Keywords: plasmonics, silicon, doping, infrared spectroscopy.

Contexte de travail

The PhD will take place at CEMES-CNRS (UPR8011) in Toulouse (https://www.cemes.fr/), within the Nano-Optics and Nanomaterials for Optics group (NeO).

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Contraintes et risques

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