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 tip-substrate separations and deviates from Couette's 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.