Scanning Electrochemical Microscopy. Hydrodynamics Generated by the Motion of a Scanning Tip and Its Consequences on the Tip Current

The motion of a SECM tip above a substrate generates a flow of the surrounding fluid. Finite element calculations show that this flow is a simple linear-shear flow (Couette flow) for small tipsubstrate separations and deviates from Couetteʹs law at larger ones. The effect of fluid flow on the tip current response was determined numerically. Different mass-transfer regimes are observed depending on the insulating or conducting nature of the substrate, the tip speed (or fluid velocity), and the tip-substrate separation. Those observations are tested experimentally, and good agreement is obtained between numerical and experimental results.