Séminaire PMMH - Jean Comtet (EPFL)

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4 octobre 2019 11:00 » 12:00 — Salle réunion PMMH 1

Soft matter and mechanics at the molecular scale : from the rheology of few-atoms gold junctions to the observation of single proton transport at solid/water interfaces.

Jean Comtet
École Polytechnique Fédérale de Lausanne,
Département Sciences et Techniques de l’Ingénieur,
CH-1015 Lausanne

New paradigms are expected to emerge at the nanometer scale for soft matter and mechanics, stemming from the breakdown of continuum concepts and the appearance of new force scales. I will present in this talk two questions related to the dynamics of soft condensed matter at the molecular scale, addressed using state-of-the-art experimental techniques.
First, I will show how we can take advantage of Quartz-Tuning Fork based Atomic Force Microscopy to uncover the yielding and rheological properties of gold junctions of only few atoms. In particular, I will show that these molecular systems exhibit a liquid-like fluidized response under large strain. This behavior challenges existing frameworks for plastic flow in defect-free crystalline systems, but exhibits surprising similarities with that of macroscopic soft yielding materials [1].
Second, I will show how we can use optical super-resolution techniques to probe the transport of single proton charges at solid/water interfaces. Our approach relies on the successive protonation and activation of optically active defects at the surface of hexagonal boron nitride crystals, allowing us to resolve interfacial proton transport at the single molecule scale with nanometric resolution and over micrometer range. These observations provide a direct demonstration that interfacial water provides a preferential pathway for lateral proton transport [2].

[1] Atomic rheology of gold nanojunctions. Nature, 1476-4687 (2019).
J. Comtet, A. Lainé, A. Niguès, L. Bocquet, A. Siria.
[2] Direct observation of water mediated single proton transport between hBN surface defects. arXiv preprint arXiv:1906.09019 (2019).
J. Comtet, B. Grosjean, E. Glushkov, A. Avsar, K. Watanabe, T. Taniguchi, R. Vuilleumier, Marie-Laure Bocquet, A. Radenovic

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