A single layer of carbon atoms, graphene, is so dense that not even helium can squeeze through—yet protons pass through it with surprising ease. This matters because the way atoms and molecules move through atom-thin membranes defies the rules that govern bulk materials. Only 4 out of more than 100 known two-dimensional crystals have been tested for permeability, leaving a vast, unexplored landscape of fundamental physics. The research aims to fill that gap by systematically investigating how different 2D lattices behave as atomic-scale sieves. If successful, the work could unlock new ways to separate ions and accelerate chemical reactions without traditional catalysts. This is fundamental science with no immediate practical application—but similar curiosity-driven research on graphene has already led to breakthroughs in water filtration, sensors, and energy storage. Understanding how matter moves through these thinnest possible membranes could eventually enable ultra-precise molecular separation for desalination, hydrogen fuel production, or medical diagnostics. For now, the goal is simply to map the rules of a world where surfaces have no bulk.
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Two-dimensional (2D) crystals are surfaces without a bulk that are stable over a wide range of conditions. Over the past years, I developed techniques that now allow using them as freestanding membranes, even in harsh environments. Despite having no bulk, these surfaces can withstand pressure differences of tens of atmospheres, separate liquids with pH differing by 14 orders of magnitude or remain stable in temperatures from a few to several hundred Celsius. 2D crystals display unusual permeation phenomena. One-atom-thick graphene is impermeable to all gases, even to the smallest, helium. Nevertheless, I found that protons, the nuclei of hydrogen atoms, readily permeate. Surprisingly, isotope or illumination effects, which are normally small or non-existent in bulk ion-transport systems, can yield order-of-magnitude effects in the 2D limit. Many fundamental questions remain open even for graphene, the most researched of these crystals - and the vast majority remain unexplored from this perspective. Enticingly, our increasing ability to engineer the 2D crystal lattice itself with atomic precision, vastly multiplies the parameters at our disposal to control permeation across these atomic scale sieves. This proposal has three aims. (1) Investigate the permeability of the vast number of 2D lattices that remain unexplored from a permeability perspective. Only 4 of the >100 known have been explored. (2) Accelerate molecular dissociation reactions in ultra-high electric fields across 2D electrodes. This physical strategy to accelerate reactions is fundamentally different to the conventional chemical catalysis route. (3) Engineer the 2D crystal lattice itself to achieve highly selective ion sieves. These groups of phenomena remain broadly inaccessible despite enormous advances in nanotechnology. Atomic scale sieves should enable access. This research direction, which I have been leading from the start, is now at a pivotal time in its development.
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