Interaction-driven giant electrostatic modulation of ion permeation in atomically small capillaries.

Abstract

Manipulating the electrostatic double layer and tuning the conductance in nanofluidic systems at salt concentrations of 100 mM or higher has been a persistent challenge. The primary reasons are (i) the short electrostatic proximity length, <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>~</mi></math> 3-10 Å, and (ii) difficulties in fabricating atomically small capillaries. Here, we successfully fabricate in-plane vermiculite laminates with transport heights of <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>~</mi></math> 3-5 Å, which exhibit a cation selectivity close to 1 even at a 1000 mM concentration, suggesting an overlapping electrostatic double layer. For gate voltages from -2 V to +1 V, the K⁺-intercalated vermiculite shows a remarkable conductivity modulation exceeding 1400% at a 1000 mM KCl concentration. The gated ON/OFF ratio is mostly unaffected by the ion concentration (10-1000 mM), which confirms that the electrostatic double layer overlaps with the collective ion movement within the channel with reduced activation energy. In contrast, vermiculite laminates intercalated with Ca²⁺ and Al³⁺ ions display reduced conductance with increasing negative gate voltage, highlighting the importance of ion-specific gating effects under Å-scale confinement. Our findings contribute to a deeper understanding of electrostatic phenomena occurring in highly confined fluidic channels, opening the way to the exploration of the vast library of two-dimensional materials.