Atomic force microscopy-scanning electrochemical microscopy: Influence of tip geometry and insulation defects on diffusion controlled currents at conical electrodes

Numerical simulations were performed to predict the amperometric response of conical electrodes used as atomic force microscopy-scanning electrochemical microscopy (AFM-SECM) probes. A simple general expression was derived which predicts their steady state limiting current as a function of their insulation sheath thickness and cone aspect ratio. Simulated currents were successfully compared with experimental currents. Geometrical parameters such as insulation angle and tip bluntness were then studied to determine their effect on the limiting current. Typical tip defects were also modeled using 3D simulations, and their influence on the current was quantified. Although obtained for SECM-AFM probes, these results are directly applicable to conical micro- and nanoelectrodes.