A differential microcantilever-based system for measuring surface stress changes induced by electrochemical reactions

We report on a differential microcantilever-based system capable of measuring surface stress changes which occur during electrochemical reactions. Surface stress changes induced by sub-monolayer ionic adsorption on metal surfaces and/or by electromechanical transformations in thin films can be measured. Our system is composed of two microcantilever sensors. The first active microcantilever serves as the working electrode (in a conventional three-probe electrochemical cell configuration) and as the mechanical transducer (bending of the microcantilever), yielding simultaneous, real-time, in situ measurements of the current and interfacial stress changes. The second reference microcantilever serves as a reference sensor to detect any unwanted cantilever deflection resulting from temperature variations, mechanical vibrations and/or uncontrolled chemical reactions. A technique for isolating the electrical contact made to the microcantilever from the electrolyte solution is presented. A method for creating a working electrode with a reproducible area of 1.0 mm2 is also described. This micromechanical cantilever sensor has a deflection sensitivity of 0.2 nm, which translates to a surface stress sensitivity of 1 × 10−4 N/m with a dynamic range of 5 × 105. The differential mode of this system has been characterized by measuring the potential-induced surface stress, at the Au(1 1 1) solid-liquid (HClO4 electrolyte) interface, during anion (ClO4−) adsorption on gold, while varying the solution temperature. Furthermore, we have measured the surface stress induced during ion doping/dedoping of dodecyl benzenesulfonate-doped polypyrrole (PPy(DBS)) films in an aqueous solution of Na(DBS).