Nanofluidic memristors process information with solvated ions rather than electrons, a route to brain-like computing in liquid. Yet why these devices "remember" their past voltage has been debated for years: ion pairing, wetting, chemistry and mechanics have all been proposed, mostly without direct evidence.
A team from EPFL, the University of Manchester, ENS Lyon and ISTA (Saurav, Ronceray, Coquinot, Emmerich, Radenovic, Radha and colleagues) has now watched the memory happen. Their devices are 2D slit channels, about 3 nm high and roughly 5 µm long, built as an hBN–graphene–hBN stack on a silicon nitride membrane. Using operando thin-film interferometry synchronised with ionic-current recordings (KCl, 1 mM to 1 M), they imaged the devices while cycling the voltage.
The finding: below about 0.2 V the response is linear and nothing moves. Above it, nanoscale liquid-filled "blisters" (heights of order 5–25 nm, micrometre-wide) open between the layers, temporarily enlarging the channel cross-section and raising conductance. Because a growing blister must overcome an adhesion barrier while a receding one does not, the height and conductance trace a hysteresis loop. That mechanical state is the memory: most deformations are volatile and collapse at 0 V, while a subset, favoured at low driving frequency (10–30 mHz), stays deformed after the bias is removed. Memory fades above roughly 100 mHz because blisters no longer have time to grow.
Two classes of blisters appear. Bidirectional ones, driven by osmotic pressure from ion concentration polarization (up to ~4 bar, height scaling as ΔV^2/3), respond to both voltage polarities. Unidirectional ones, driven by electrostatic force on weakly screened surface charges (up to ~3 bar, height scaling as ΔV^1/3), respond to one polarity only. Across 50 blisters in nine devices, the two populations separate cleanly. One device showed an ON/OFF ratio of 50, and individual blisters could be tied to abrupt conductance jumps of about +50% in under a second.
Why it matters for neuromorphic matter: the stochastic nucleation of blisters explains the notorious device-to-device variability of nanofluidic memristors, and turns it into a design handle. Deterministically placed low-adhesion zones could give reproducible ionic synapses, with the electromechanical coupling echoing the conformational gating of biological ion channels.
Paper: Saurav, Ronceray, Coquinot et al., "Direct imaging elucidates ionic memory in two-dimensional nanochannels," Nature Materials (published 27 October 2026), DOI: 10.1038/s41563-026-02775-4 — https://www.nature.com/articles/s41563-026-02775-4
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