Fabrication of Submicrometer-Sized Gold Electrodes of Controlled Geometry for Scanning Electrochemical-Atomic Force Microscopy

Abstract

A method for fabricating submicrometer-sized gold electrodes of conical or spherical geometry is described. By generating an electric arc between an etched gold microwire and a tungsten counter electrode, the very end of the gold microwire can be melted and given an overall spherical or conical shape a few hundred nanometers in size. The whole wire is subsequently insulated via the cathodic deposition of electrophoretic paint. By applying a high-voltage pulse to the microwire, the film covering its very end can then be selectively removed, thus exposing a submicrometer-sized electrode surface of predefined geometry. The selective exposure of the preformed end of the microwire is demonstrated by cyclic voltammetry, scanning electron microscopy, and metal electrodeposition experiments. The electrophoretic paint coating provides a low-capacitance, robust insulating film allowing exploration of a very wide potential window in aqueous solution. The submicrometer-sized electrodes can easily be turned into probes suitable for combined scanning electrochemical-atomic force microscopy by bending and flattening the gold microwire so that the tip is borne by a flexible enough arm. The good agreement between theoretical and experimental scanning electrochemical microscopy approach curves thus obtained confirms that only the very end of the tip, of predefined geometry, is exposed to the solution.

Applications of Scanning Electrochemical Microscopy (SECM) Coupled to Atomic Force Microscopy with Sub-Micrometer Spatial Resolution to the Development and Discovery of Electrocatalysts

“…Thus, the combined AFM-SECM technique using an AFM cantilever with a conductive coating as the tip electrode for SECM has led to recent progress [55][56][57][58][59][60][61][62][63]. A number of approaches have been attempted in order to use the conductive cantilever as the tip electrode, with the objective to confine the active tip area of the AFM cantilever.…”

“…In order to construct tip electrodes to broaden the application of AFM-SECM to a scope similar to that of the UME, tip electrodes have been prepared via mechanical (or chemical) insulation of the conductive cantilever [56,57]. In these methods, most of the conducting area of the cantilever was covered by employing various techniques, e.g., physical insulation by polymer films or electrophoretic deposition of chemicals, followed by mechanical abrasion or electric discharge methods to expose the end of the tip as the active electrode [56,57,59,60].…”

Simultaneous imaging of the topography and electrochemical activity of a 2D carbon nanotube network using a dual functional L-shaped nanoprobe

“…SECM-AFM has been used to study the local electrochemical activity of various substrates, enzyme activity, [20][21][22] and membrane ion transport. 8,23,24 Furthermore, SECM-AFM probes with nanoelectrodes have been developed to improve the electrochemical resolution; 12,13,15,[25][26][27][28][29][30] however, the application of high-resolution SECM-AFMs with disk-type nanoelectrodes is limited to the characterization of probes using the "lift-up" mode to avoid short circuiting. 27,30 In the lift-up mode, the probe tip is lifted from the substrate by a predefined distance to collect electrochemical data while tracing the surface topography recorded in the previous surface scan during which the probe was in contact with the surface.…”

Electrochemically etched sharp aluminium probes with nanoporous aluminium oxide coatings: demonstration of addressed DNA delivery

“…6 Tungsten, platinum-iridium, gold, and silver are the most commonly used materials for nanoprobe fabrication. 7 A sharp tip with a nanoporous structure has a signi-cantly increased surface area. This feature enables controlled access and realisation of immobilisation and other processes on the local scale.…”