Electrochemical Characterisation of Nanoscale Liquid|Liquid Interfaces Located at Focused Ion Beam‐Milled Silicon Nitride Membranes

Abstract

The electrochemical behaviour of single and arrayed nanoscale interfaces between two immiscible electrolyte solutions (single and array nanoITIES) is presented. The interfaces were formed at nanopores fabricated through the focused ion beam (FIB) milling of silicon nitride (SiN) membranes by using nanopores with approximately 30–80 nm radii and with pore‐to‐pore separations to pore radius ratios in the range of 16–32. Electrochemistry was performed through the interfacial transfer of tetrapropylammonium (TPrA+) across single and array nanoITIES between water and 1,6‐dichlorohexane. The ion‐transfer limiting current at the single nanoITIES was in excellent agreement with the current predicted by using an inlaid disc interface model. At nanoITIES arrays, experimental currents were lower than predicted for an array of inlaid interfaces, which is attributed to overlapped diffusion zones. As a result, FIB milling offers an attractive strategy to form nanoITIES for diverse investigations.

Achievement of Diffusional Independence at Nanoscale Liquid–Liquid Interfaces within Arrays

“…31 This direct-write technique provides an alternative approach 32,33 to other nanofabrication methods based on high-energy particle beams, such as electronbeam lithography, which requires more complex and timeconsuming procedures. Figure 1A−E shows the SEM images of the five nanopore square array designs with r c /r a of 13 (A), 38 (B), 56 (C), 70 (D), and 82 (E).…”

A Newly Synthesized Tris(crown ether) Ionophore for Assisted Ion Transfer at NanoITIES Electrodes

“…An Ag wire (diameter=250 μm) coated with AgCl (through an oxidation reaction in saturated KCl solution) was placed in the aqueous phase as an outside reference electrode. A two electrode configuration was used as reported previously, where a potential was applied between the inner Pt wire and the outer Ag/AgCl reference electrode . Positive potential is for positive ion transfer from water to oil (1, 2‐DCE), seen as positive current.…”

Decorating soft electrified interfaces: From molecular assemblies to nano-objects

“…Inspired by ion transport in nature, the control of mass transfer through arrays of solid-state nanopores (typically with a diameter ranging from 10 to 200 nm) has been investigated at the liquidliquid interface [181,182]. The preparation of arrays of nano-interfaces has been achieved by either electron beam lithography [183] or by focused ion beam milling [184] through silicon nitride membranes (50-100 nm thick). Mass transport over such nano-arrays is improved resulting in an increase of sensitivity per unit area compared to interfaces in the micron or centimetre scale [185].…”

“…Indeed, when the dimension of the interface is smaller than the diffusion layer thickness (typically a few tens of microns), mass transfer is greatly improved by the shift from a linear to a radial diffusion profile. Fabricated arrays of micro and nanointerfaces have been developed to harness the benefits of greater mass transport to the sensitivity improvement of ion detection at the ITIES [183][184][185][186][187][188][189][208][209][210]. If the transition of macro-ITIES to its micron size counterpart has improved the limits of detection of one or two orders of magnitude, pushing further the limits of detection by reducing the physical dimension of liquid-liquid interfaces down to the nanometre scale has proven difficult to achieve [189].…”