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

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Controlling ion transport in nanofluidic systems at high salt concentrations (>100 mM) is challenging due to short electrostatic double-layer lengths and fabrication difficulties.
• Atomically small capillaries are difficult to create, hindering precise manipulation of electrostatic double layers.

Purpose of the Study:

• To fabricate and characterize Å-scale vermiculite nanofluidic channels capable of high salt concentration operation.
• To investigate cation selectivity and conductivity modulation in these confined systems.
• To explore ion-specific gating effects in Å-scale confinement.

Main Methods:

• Fabrication of in-plane vermiculite laminates with transport heights of 3-5 Å.
• Measurement of cation selectivity and conductivity modulation using applied gate voltages.
• Analysis of ion-specific gating effects with different intercalated cations (K+, Ca2+, Al3+).

Main Results:

• Vermiculite channels exhibited cation selectivity close to 1 even at 1000 mM salt concentration, indicating overlapping electrostatic double layers.
• K+-intercalated vermiculite showed over 1400% conductivity modulation at 1000 mM KCl with gate voltages from -2 V to +1 V.
• The gated ON/OFF ratio remained largely unaffected by ion concentration (10-1000 mM), confirming electrostatic double-layer overlap and reduced activation energy.
• Ca2+- and Al3+-intercalated vermiculite showed reduced conductance with negative gate voltage, highlighting ion-specific effects.

Conclusions:

• Successfully fabricated Å-scale nanofluidic channels using vermiculite laminates.
• Demonstrated effective control over ion transport and conductivity modulation in high salt concentration regimes.
• Provided insights into electrostatic phenomena and ion-specific gating in highly confined systems, relevant for two-dimensional material applications.