Microfabricated recessed microdisk electrodes: Characterization in static and convective solutions

Construction and characterization of microfabricated recessed microdisk ele ctrodes (RMDs) of 14- and 55-mu m diameters and 4-mu m depth are reported. For evaluation of electrode function, both faradaic current in RU(NH3)(6)(3 +)-/KNO3 solution and charging current in KNO3 solution were measured with cyclic voltammetry. The experimental maximum current was measured and compa red to calculated values, assuming radial and linear diffusion. A model for diffusion to a RMD best matches the behavior of the 14-mu m RMD, which has a larger depth-to-diameter ratio than the 55-mu m RMD. At fast scan rates (204 V s(-1)), where linear diffusion should dominate, there are large devi ations from the linear diffusion model. Uncompensated resistance and overco rrection for background current contribute to this deviation. The dependenc e of capacitance on scan rate of the RMDs was found to be similar to that o f a macroelectrode, indicating good adhesion between the insulator and the electrode. Chronoamperometry of RU(NH3)(6)(3+) in KNO3 in both static and s tirred solutions was performed using the RMDs and the current is compared t o those from a 10-mu m-diameter planar microdisk electrode (PMD). The signa l-to-noise ratio of the 14-mu m RMDs compared to the PMD is on average 4 ti mes greater for stirred solutions. The 55-mu m RMD exhibited no protection to convection of the stirred solution.