M/F

Job Description

Thesis Subject

Experimental Investigation of Topological Elastic Wave Transport in Nanostructured Metamaterials

Your Work Environment

Topological elastic metamaterials provide a novel platform for controlling the propagation of mechanical waves. By exploiting topological properties, these structures offer unique opportunities for robust wave guiding, acoustic filtering, and the development of high-precision sensing technologies. The objective of this PhD project is to experimentally investigate topological transport of elastic waves in nanostructured metamaterials, with a particular focus on two types of waves:

* **Rayleigh waves**, propagating along the surface of silicon substrates;
* **Lamb waves**, confined within nanostructured Si or SiN membranes.

The results will contribute to the development of ultra-robust mechanical waveguides and enhanced acoustic sensing systems. In the longer term, this research may also pave the way for applications in communication technologies and elastic-wave-based filtering devices.

### Experimental Approach

#### 1. Sample Fabrication

The design and fabrication of topological membranes and phononic crystals will rely on lithography, ion etching, and chemical etching techniques, carried out in collaboration with the Centre for Nanoscience and Nanotechnology (C2N). The geometry and quality of the nanostructures will be optimized through extensive characterization using atomic force microscopy (AFM), scanning electron microscopy (SEM), and ellipsometry.

#### 2. Wave Generation and Detection

Non-contact excitation and sub-micrometer characterization of elastic modes will be performed using the **picosecond ultrasonics** technique. A spatial light modulator (SLM) will be employed to tailor the direction and frequency content of the generated waves. High-precision detection will rely on optical interferometry and ultrasonic spectroscopy, providing the sensitivity required to investigate the expected topological phenomena.

#### 3. Investigation of Robustness and Topological Modes

The project will focus on guided wave propagation and on localized modes supported by topological interfaces. Particular attention will be paid to the influence of structural defects on wave robustness. Experimental results will be systematically compared with theoretical models in collaboration with the Institute of Electronics, Microelectronics and Nanotechnology (IEMN), with the goal of optimizing the design of topological structures and achieving precise control of elastic-wave transport.

Constraints and risks

This PhD project is primarily experimental and involves the development and optimization of nanostructured devices, as well as the implementation of advanced optical and picosecond ultrasonic techniques. The successful candidate will work in a cleanroom environment (in collaboration with C2N), perform highly sensitive measurements, and analyze complex experimental datasets.

A significant part of the research will focus on adapting and refining experimental protocols and comparing experimental observations with theoretical predictions. The project therefore requires a high level of scientific rigor, autonomy, problem-solving skills, and a strong interest in hands-on experimental research.

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

The research professions