Alternating morphology transitions between dendrite and dense-branching morphology have been studied for the first time in electrochemical deposition of FeSO4 aqueous solution film. We suggest that the observed alternating transition is caused by the interchange of anisotropy in interfacial growth, which arises from the periodic accumulation and depletion of impurities in front of the growing interface in our experimental system. The selection problem In pattern formation is discussed.

In this Letter we report a unique fractal aggregation behavior of NH4Cl crystallites grown in agarose gel. The fractal branches consist of faceted crystallites with remarkable correlations in their crystallographic orientations, which are formed by successive heterogeneous nucleations. Unlike the conventional fractal growth, this aggregation process occurs at a low growth driving force with strong crystallographic anisotropy, which leads to the ordering in the fractal branches. [S0031-9007 (98) 05675-0]

ELECTRODEPOSIT1ON of metals such as copper and zinc from solutions of their salts may give rise to ramified metal deposits which show a range of growth morphologies1-9. Our understanding of the factors that determine growth morphology is still very limited, in part because different morphologies may be observed even under similar growth conditions 4,5. It is thought9 that uncontrolled convective processes at the tips of the deposit branches may play a role in these discrepancies. Here we show that convective effects, which we can visualize directly, in the electrodeposition of iron from FeSO4 solution, can generate a mesh-like pattern, a morphology that has not been reported previously. Convection can be diminished by altering the pH, whereupon we see a transition to a dense branching morphology. Our results show that convective effects do indeed play an important part in determining pattern selection during electrodeposition.

In this article we report the systematic studies on the oscillation of contrast in front of a growing zinc dendrite in electrochemical deposition observed with interference contrast microscopy. The dependence of the oscillation frequency on the experimental conditions, such as the electric current, the resistance of ion transfer, pH of the electrolyte and the tilting of the electrodeposition cell, etc., has been investigated. The microstructures of the electrodeposits are analyzed with transmission electron microscopy. We conclude that the contrast oscillation in front of the zinc deposit is indeed associated with the concentration oscillation, and is synchronized with the electric voltage/current signals. Although the oscillation can be affected by mass transport in the system, we suggest that it roots from the alternating deposition of zinc and zinc hydroxide on the deposit-electrolyte interface.

In this paper we report the spontaneous formation of a nanostructured film by electrodeposition from an ultrathin electrolyte layer of CuSO4. The film consists of straight periodic ditches and ridges, which corresponds to the alternating deposition of nanocrystallites of copper and copper plus cuprous oxide, respectively. The periodicity on the film may vary from 100nm to a few hundred nanometers depending on the experimental conditions. In the formation of the periodically nanostructured film, oscillating voltage/current has been observed across the electrodes, and the frequency depends on the pH of the electrolyte and the applied current/voltage. A model based on the coupling of [Cu2+] and [H+] in the electrodeposition is proposed to describe the oscillatory phenomena in our system. The calculated results are in agreement with the experimental observations.