Ion-transfer voltammetry at silicon membrane-based arrays of micro-liquid–liquid interfaces

Abstract

Microporous silicon membranes, fabricated by lithographic patterning and wet and dry silicon etching processes, were used to create arrays of micro-scale interfaces between two immiscible electrolyte solutions (mITIES) for ion-transfer voltammetry. These membranes served the dual functions of interface stabilization and enhancement of the rate of mass-transport to the interface. The pore radii were 6.5 mm, 12.8 mm and 26.6 mm; the pore–pore separations were ca. 20- to 40-times the pore radii and the membrane thickness was 100 mm. Deep reactive ion etching (DRIE) was used for pore drilling through the silicon, which had been previously selectively thinned by potassium hydroxide etching. DRIE produces hydrophobic fluorocarbon-coated internal pore walls. The small pore sizes and large pore–pore separations used resulted in steadystate voltammograms for the transfer of tetramethylammonium cation (TMA+) from the aqueous to the organic phase, whereas the reverse voltammetric sweeps were peak-shaped.