Photoacoustic MEMS resonant gas sensor

Chronic respiratory diseases are among the most common noncommunicable illnesses worldwide, largely due to harmful environmental, occupational, and lifestyle exposures [James2017]. In 2017, the European Respiratory Society (ERS) defined research priorities in breath biomarkers [Horvath2017], recommending technologies for selective recognition of gases and standardized real-time procedures to assess pulmonary function. Currently, only a few electrochemical sensors exist for exhaled breath. They are sensitive but poorly selective, detecting only limited gases. In hospitals, nitric oxide (NO) is the sole breath biomarker used in pulmonary disease diagnosis. CO₂, CO, and O₂ are occasionally measured in high concentrations under specific protocols to evaluate mechanisms such as alveolar diffusion. Except for capnography (CO₂), no equipment provides real-time measurements across respiratory zones like trachea or alveoli.

This thesis aims to develop a compact, ultra-sensitive, and selective photoacoustic gas sensor. Photoacoustic spectroscopy (PAS) detects gases by measuring their absorption lines. A laser tuned to the target gas wavelength produces local heating and pressure variations, recorded by an acoustic detector (microphone, cantilever, quartz tuning fork, or MEMS). Detection is independent of optical wavelength and path length, enabling work on very small gas volumes and rapid detection. The proposed structure employs a resonant strain gauge, whose frequency shifts with membrane deformation under acoustic excitation.

Funding is already available and the PhD may start as soon as the adequate candidate is found and selected. Starting with an internship starting in March or April 2026 is also possible for candidates who are still Master students at the time of application.

The Centre for Nanosciences and Nanotechnology (C2N) is a joint research unit between the CNRS and Université Paris-Saclay. It was founded on the 1stJune 2016 by merging two former laboratories, the Laboratoire de Photonique et de Nanostructures (LPN) and the Institut d’Electronique Fondamentale (IEF). In 2018, the laboratory moved to a new building at the heart of Campus Paris-Saclay, in the south of Paris.

C2N lab is a restricted area. Selected candidates will be subject to an inquiry by a French Defence office before having the chance to be recruited. Please be aware that some nationality-related conditions may apply when joining C2N.

This multidisciplinary project involves several fields, including:

• Mechanics: linear and nonlinear resonators, solid understanding of acoustic phenomena and structural vibrations, analytical modeling and finite element analysis.
• Electronics: test benches including signal generators, synchronous detection, phase-locked loops, oscilloscopes, computer interfacing, etc.
• Optics: even though most of the work is not dedicated to optics, understanding the principles behind the photoacoustic phenomenon is essential. The candidate should also be motivated to improve his/her skills in optical metrology at the micro/nanoscale.
• Cleanroom fabrication processes: willingness to work on the fabrication and characterization of devices in cleanroom conditions, including lithography, etching, microscopy observations, and optical characterization of moving nanostructures.

It is of course not required that the candidate be fully proficient in all these areas, but she/he should be motivated to explore them. Skills in optics (particularly experimental know-how) and experience with vacuum testing would be considered an asset. Knowledge of Matlab and/or Python would also be a plus.