Laboratoire SIMM, ESPCI Paris, PSL University, CNRS, Sorbonne Université, 75231 Cédex 05 Paris, France
“Watching single charges moving at solid/liquid interfaces”
Understanding the dynamics of charge exchange and transport between a liquid electrolyte and a solid surface is essential for a number of domains, both fundamental (biophysics, nanofluidics, catalysis, electrochemistry…) and applicative (energy storage, energy harvesting, filtration…). However, we remain mostly blind to these interfacial processes, which are currently probed through indirect and ensemble-averaged measurements, hindering their basic understanding.
I will present here recent experimental efforts to resolve interfacial charge dynamics at solid/liquid interfaces at the single-molecule scale, combining Single-Molecule and Super-Resolution microscopy techniques with fluorescent defects hosted in hexagonal Boron Nitride crystals. Starting with aqueous solvents, we reveal single proton charge trajectory at the interface through the successive activation of ionizable fluorescent surface defects. These observations allow us to resolve interfacial charge transport with nanometric resolution and over micrometer range, providing experimental evidence at the single molecule scale that interfacial water provides a preferential pathway for lateral charge transport. We then extend these experiments towards more complex solvents, and probe the role of nanometric confinement on molecular charge transport.
 Direct observation of water-mediated single-proton transport between hBN surface defects. Comtet, J., Grosjean, B., Glushkov, E., Avsar, A., Watanabe, K., Taniguchi, T., … & Radenovic, A. Nature Nanotechnology, 15(7), 598-604. (2020).
 Comtet, J., Rayabharam, A., Glushkov, E., Zhang, M., Avsar, A., Watanabe, K., … & Radenovic, A. Anomalous interfacial dynamics of single proton charges in binary aqueous solutions. Science advances, 7(40), eabg8568. (2021).
 Ronceray, N., You, Y., Glushkov, E., … Keerthi, A., Comtet, J., Radha, B., Radenovic A. (2022). Liquid-activated quantum emission from native hBN defects for nanofluidic sensing. arXiv preprint arXiv:2204.06287.