Quasi-Stable Salt Gradient and Resistive Switching in Solid-State Nanopores

Abstract

Understanding and control of ion transport in a fluidic channel is of crucial importance for iontronics. The present study reports on quasi-stable ionic current characteristics in a SiNx nanopore under a salinity gradient. An intriguing interplay between electro-osmotic flow and local ion density distributions in a solid-state pore is found to induce highly asymmetric ion transport to negative differential resistance behavior under a 100-fold difference in the cross-membrane salt concentrations. Meanwhile, a subtle change in the salinity gradient profile led to observations of resistive switching. This peculiar characteristic was suggested to stem from quasi-stable local ion density around the channel that can be switched between two distinct states via the electro-osmotic flow under voltage control. The present findings may be useful for neuromorphic devices based on micro- and nanofluidic channels.

Selective Ion Enrichment and Charge Storage through Transport Hysteresis in Conical Nanopipettes

“…Enrichment and depletion of ions, that is, concentration polarization (CP), under external electrical potential control lead to rectified electrokinetic transport in single asymmetric nanopores, nanopipettes, asymmetric nanochannels, or arrays/membranes. − A notable steady-state phenomenon related to CP is ion current rectification (ICR) where the ionic current is higher at one potential polarity over the opposite. , The dynamics of the CP or ICR displays features such as transport hysteresis, current oscillation, and state-switching among others. − Novel electrokinetic transport phenomena such as electroosmotic flow (EOF) rectification and negative differential resistance , are also observed associated with CP. One of the foundational problems remains to address the physiochemical origin of the hysteresis charges at both qualitative and quantitative levels that change in different time scales and ionic strengths for a given nanodevice or membrane/materials platform.…”

Perspective on Nanofluidic Memristors: From Mechanism to Application

“…Leong et al. realized a memristive system based on a nanopore with asymmetric solutions of different concentrations, [52] as shown in Figure 5A. Under the control of EOF, the nanopore in salt gradient showed hysteric ion concentration variation which lasts for a short moment owing to the diffusion limitation of ions, exhibiting potential of emulating behaviors of neurons with this EOF based strategy as shown in Figure 5B.…”

“…[49,50] With this mechanism, Luo et al achieved NDR effect by rational tuning EOF/convective flow balance in asymmetric solution, [51] indicating the possibility of forming nonlinear ion transport behaviors with this dynamic. Leong et al realized a memristive system based on a nanopore with asymmetric solutions of different concentrations, [52] as shown in Figure 5A. Under the control of EOF, the nanopore in salt gradient showed hysteric ion concentration variation which lasts for a short moment owing to the diffusion limitation of ions, exhibiting potential of emulating behaviors of neurons with this EOF based strategy as shown in Figure 5B.…”

“…The emulation of this interaction-based dynamic is of great (A) Quasi-interface formed between asymmetric solutions of different concentrations. [52] (B) Hysteresis I-V curve observed in asymmetric solutions of different concentrations. [52] (Copyright 2020, American Chemical Society) (C) The dynamic of IL/solution interface movement.…”

From Water Solutions to Ionic Liquids with Solid State Nanopores as a Perspective to Study Transport and Translocation Phenomena

“…[66] This effect might be related to diffusio-osmotic flows in salt gradients and the effects of low hydraulic resistance and pore edge effects in the case of nanopores in 2D materials. [67,68] One of the major questions arising here for ILs is the nature of the double layer and the effective surface zeta potential. Although electro-osmotic flow should be diminished in the ILs by the increased viscosity and high structuring inside the nanopore, it is not clear what happens when ILs is in contact with different fluid, such as aqueous solution, or other type of ILs (see Figure 1b,c).…”