Nature of inclined growth in thin-layer electrodeposition under uniform magnetic fields

Abstract

Electrochemical deposition (ECD) in thin cells in a vertical position relative to gravity, subject to an externaluniform magnetic field, yields a growth pattern formation with dense branched morphology with branches tiltedin the direction of the magnetic force. We study the nature of the inclined growth through experiments andtheory. Experiments in ECD, in the absence of magnetic forces, reveal that a branch grows by allowing fluid topenetrate its tip and to be ejected from the sides through a pair of symmetric vortices attached to the tip. Theupper vortices zone defines an arch separating an inner zone ion depleted and an outer zone in a funnel-likeform with a concentrated solution through which metal ions are carried into the tip. When a magnetic field isturned on, vortex symmetry is broken, one vortex becoming weaker than the other, inducing an inclination ofthe funnel. Consequently, particles entering the funnel give rise to branch growth tilted in the same direction.Theory predicts, in the absence of a magnetic force, funnel symmetry induced through symmetric vortices drivenby electric and gravitational forces; when the magnetic force is on, it is composed with the pair of clockwiseand counterclockwise vortices, reducing or amplifying one or the other. In turn, funnel tilting modifies particletrajectories, thus, growth orientation.