Engineered Two-Dimensional Voids as Angstrom-Scale Capillaries

2D-materials are well known for their extraordinary properties and graphene is an archetypal example with most superlatives to its credit for the description of its properties, thinnest, strongest, most conducting, lightest etc. On the contrary, angstrom-scale capillary can be dubbed as “2D-nothing”; it is an antipode of graphene, created by focusing on what is left behind after extracting one-atomic layer out of a crystal [1]. Angstrom-size capillaries are constructed out of 2D-materials, and we investigate properties of gas, liquids and ions confined in molecular scale. A core strand of the work that I will present is the development of Angstrom-capillaries as a platform to probe intriguing molecular-scale phenomena experimentally, including: water flow under extreme atomic-scale confinement [1] complete steric exclusion of ions [3,5], specular reflection and quantum effects in gas reflections off a surface [2,7], voltage gating of ion flows [4] translocation of DNA [6]. Previously theoretical simulations modelled such phenomena and this is the first robust experimental platform with controlled angstrom-scale dimensions made from atomically smooth building blocks, alleviating the surface roughness which usually predominates at this scale. Moreover these Å-capillaries represent two-dimensional analogues of artificial sub-nanometer fluidic conduits.<br/>This work was done in collaboration with A.K. Geim, A. Keerthi, K. Gopinadhan, A. Esfandiar, S. Goutham, F.C. Wang, S. J Haigh from University of Manchester, and with L. Bocquet, T. Mouterde, A. Poggioli, A. Siria, from Micromégas team, ENS Paris.<br/><u>References:</u><br/>[1] B. Radha et al., Molecular transport through capillaries made with atomic-scale precision. <b><i>Nature</i></b> 538, 222<br/>(2016).<br/>[2] A. Keerthi et al., Ballistic molecular transport through two-dimensional channels, <b><i>Nature</i></b> (2018), 558, 420.<br/>[3] A. Esfandiar et al., Size effect in ion transport through angstrom-scale slits. <b><i>Science</i></b> 358, 511 (2017).<br/>[4] T. Mouterde et al., Molecular streaming and voltage gated response in Angstrom scale channels. <b><i>Nature</i></b> 567,<br/>87 (2019).<br/>[5] K. Gopinadhan et al., Complete ion exclusion and proton transport through monolayer water. <b><i>Science</i></b> 363,<br/>145 (2019).<br/>[6] W. Yang et al., Translocation of dna through ultrathin nanoslits. <b><i>Advanced Materials</i></b> 2007682, (2021).<br/>[7] J. Thiruraman et al., Gas flows through atomic-scale apertures, <b><i>Science Advances </i></b>6, eabc7927, (2020)<br/><b>Acknowledgements</b><br/>B.R. acknowledges the funding from Royal Society university research fellowship and enhancement award RGF\EA\181000, and funding from the European Union’s H2020 Framework Programme/ERC Starting Grant agreement number 852674 - AngstroCAP.