Towards sub-second Solution Exchange Dynamics in Liquid-Phase TEM Flow Reactors

Abstract Liquid Phase-Transmission Electron Microscopy research increasingly relies on liquid flow reactors to monitor nanoscale dynamics. Current challenges comprise fast mass transport dynamics inside the central nanochannel of the liquid cell, typically flow cells, and reliable fixation of the specimen in the limited imaging area. In this work, we present a novel liquid cell concept, the diffusion cell, that satisfies these seemingly contradictory requirements by providing additional on-chip bypasses to allow high convective transport around the nanochannel in which the diffusive transport predominates. Diffusion cell prototypes were developed using numerical mass transport models and fabricated on the base of existing two-chip MEMS-setups. Important hydrodynamic parameters such as the total flow resistance, the flow velocity in the imaging area and the time constants of mixing were improved by ~2-3 orders of magnitude compared to existing setups. Obtained solution replacement dynamics within seconds already matches the mixing timescales of many ex situ scenarios, with further improvements possible. Diffusion cells can be easily integrated into existing Liquid Phase Transmission Electron Microscopy workflows, provide correlation of results with ex-situ experiments, and can create entirely new research directions for fast nanoscale processes in liquids.