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

École Polytechnique Fédérale de 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 rheological properties of gold junctions of only few atoms. In particular, I will show that these molecular systems exhibit a liquid-like fluidized response at large strain, in striking similarity with the behavior of soft macroscopic yielding materials [1].
Second, I will show how we can use super-resolution optical 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 demonstrate 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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