Controlling nanoslot overlimiting current with the depth of a connecting microchamber

The overlimiting ion flux, in excess of the limiting-value stipulated by diffusion, across a wide nanoslot (of fixed depth) is shown to be sensitively dependent on the depth of the connecting microchamber at one end of the nanoslot, which controls the onset of a vortex instability that specifies the dimension of the concentration polarization layer responsible for overlimiting behavior. Simple scaling arguments relating the microchamber depth to the effective fluid viscosity produce experimentally verified scaling dependence of the polarization layer length, the onset voltage for overlimiting behavior and the overlimiting current on the microchamber depth.