Pattern selection induced by electroconvection in the electrodeposition of iron

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

Electrochemical deposition (ECD) in thin cells in a vertical position relative to gravity, subject to an external uniform magnetic field, yields a growth pattern formation with dense branched morphology with branches tilted in the direction of the magnetic force. We study the nature of the inclined growth through experiments and theory. Experiments in ECD, in the absence of magnetic forces, reveal that a branch grows by allowing fluid to penetrate its tip and to be ejected from the sides through a pair of symmetric vortices attached to the tip. The upper vortices zone defines an arch separating an inner zone ion depleted and an outer zone in a funnel-like form with a concentrated solution through which metal ions are carried into the tip. When a magnetic field is turned on, vortex symmetry is broken, one vortex becoming weaker than the other, inducing an inclination of the 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 driven by electric and gravitational forces; when the magnetic force is on, it is composed with the pair of clockwise and counterclockwise vortices, reducing or amplifying one or the other. In turn, funnel tilting modifies particle trajectories, thus, growth orientation.

Transition between two dendritic growth mechanisms in electrodeposition

We report in this paper the observation of a transition between two different dendritic growth mechanisms in the electrodeposition of a metal from a binary electrolyte. Our results, in particular concerning the dendritic growth velocities, enable us to explain this behavior in terms of models previously proposed in the literature.

Alternating morphology transitions in crystallization of NH4Cl on agar plates

Two types of alternating morphology transitions have been observed in crystallization of NH4Cl on agar plates. One is the alternating morphology transitions between dense branching morphology and sparse branching morphology, and the other is the alternating morphology transitions between dense branching morphology and zigzag branching morphology. The appearance of them is found to depend on the mass proportion of agar to NH4Cl in the initial solution and the relative humidity. It is suggested that both the two alternating morphology transitions result from the oscillation of solute concentration in front of the growing interface caused by the competition of crystal growth and solute transfer at a moderate mass proportion. Which one of them occurs depends on the relative humidity, which controls the supersaturation.

Noise-reduced electroless deposition of arrays of copper filaments

We report here a self-organized electroless deposition of copper in an ultrathin layer CuSO4 of electrolyte. Microscopically the branching rate of the copper deposits is significantly decreased, forming an array of smooth polycrystalline filaments. Compared with a conventional electrodeposition system, no macroscopic electric field is involved and the thickness of the electrolyte layer is greatly decreased. Therefore the electroless deposition takes place in a nearly ideal, two-dimensional diffusion-limited environment. We suggest that restriction of the thickness of the electrolyte film is responsible for the generation of smoother branches of the electrodeposits. Our data also show that even in a diffusion-limited scenario the aggregate morphology is not necessarily very ramified and fractal-like.

Electrochemical growth of iron and cobalt arborescences under a magnetic field

Pattern formation in the electrochemical deposition of the magnetic Fe and Co metals from thin layers of Fe(SO4) or Co(SO4) aqueous solutions were investigated in circular geometry and under magnetic field. Sparse arborescences with few thick branches and dense arborescences with many thin branches can be generated when no magnetic field is applied. Unlike for nonmagnetic metals, no tendency towards growth spiraling or asymmetric branching is found out in magnetic field normal to the plane of the growth. The morphology of the deposits appears instead to become more sparse. Under in-plane magnetic field, the sparse arborescences get into a needle morphology, oriented along the field, while the dense arborescences show a circular to rectangular morphology symmetry breaking, one edge of the rectangle being parallel to the field. Unexpected in most instances, these magnetic field effects cannot be understood without invoking the magnetic dipolar interaction inside the magnetized growing aggregate together with its interaction with the applied field.

Formation of nanostructured copper filaments in electrochemical deposition

In this paper, we report in detail the studies of a different self-organized copper electrodeposition carried out in an ultrathin layer of CuSO4 electrolyte. On a macroscopic scale, the morphology of the electrodeposit is fingerlike. Microscopically, each fingering branch consists of long, straight copper filaments with periodic corrugated nanostructures. Branching rate of the electrodeposit is significantly decreased, compared with the patterns grown in conventional systems. Detailed information of the growth environment in the ultrathin electrodeposition system is provided, the formation mechanism of the periodic nanostructures on the deposit filaments is explored, and the origin of the significant descent of branching rate of the electrodeposit is discussed.

Nanostructured copper filaments in electrochemical deposition

In this Letter we report a novel self-organized copper electrodeposition in an ultrathin layer of CuSO4 electrolyte. The macroscopic fingering branches of the deposit consist of long copper filaments covered with periodic corrugated nanostructures. The mechanism of the nanostructure formation is explored and the origin of the significant descent of the branching rate in electrodeposition is discussed. We suggest that this growth phenomenon provides deeper insights into the role of diffusion and migration on pattern formation in electrodeposition.