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.

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 situ observations technique is evmloyed to study the freatctal growth in a thin isothermal aqueous-soulution film of Ba(NO3)2. The micromorphology and the growing process of the fractals have been investigated. The experimental findings provide direct evidence that the fractals are formed by random successive nucleation. A nucleation-limited-aggregation (NLA) model is proposed to describe the fractal growth in our system. A computer simuation using the NLA model is also presented.

Noise-reduced electrodepostion is performed in an agarose gel medium containing CuSO4 solution. Instead of random fractal-like patterns usually seen in CuSO4 aqueous solution electrodeposition, the deposit shows a smore ordered morphology. The dendritic pattern with and evident main stem can be seen. Alternating tip splitting has been observed druing the dedritic growth. It is suggested that the suppression of convective noise near the growing interface is responsibel for the appearance of dendrites in this experiment. The alternating dendrite tip splitting is interpreted as the reslut of altenating accumuation adn depletion of imprutites in front of the growing interface.

The dynamic behavior of the concentration field in crystallization is investigated by considering the coupling of the bulk concentration field and interfacial kinetics. It is shown that the concentration field may become unstable for perturbations with certain wavelength. When instability occurs, the physical environment in front of the growing interface will fluctuate and the interfacial growth mode will be affected accordingly. We suggest that our analysis can be used to interpret some spatial-temporal instabilities observed in crystallization.