Microfabricated recessed microdisk electrodes: Characterization in static and convective solutions

Construction and characterization of microfabricated recessed microdisk electrodes (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 compared 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 deviations from the linear diffusion model. Uncompensated resistance and overcorrection for background current contribute to this deviation. The dependence of capacitance on scan rate of the RMDs was found to be similar to that of a macroelectrode, indicating good adhesion between the insulator and the electrode. Chronoamperometry of RU(NH3)(6)(3+) in KNO3 in both static and stirred solutions was performed using the RMDs and the current is compared to those from a 10-mu m-diameter planar microdisk electrode (PMD). The signal-to-noise ratio of the 14-mu m RMDs compared to the PMD is on average 4 times greater for stirred solutions. The 55-mu m RMD exhibited no protection to convection of the stirred solution.