CONTROL OF MESOSCOPIC STRUCTURE OF ELECTRODEPOSITED IRON-GROUP METAL FILM BY DEPOSITION OVERPOTENTIAL

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The mesoscopic structure of cobalt electrodeposited under galvanostatic conditions was investigated using XRD and SEM.The results obtained are to be as follows ;(1) The cobalt deposits from sulfate baths consisted of well-defined hexagonal platelets, resulting in the preferred (002) orientation at both high current density and high temperature. The predominant orientation of (110) plane was observed, on the other hand, at low current density and low temperature. These results was able to be well explained by Pangarov's two-dimentional nucleation hypothesis which clarify the relationship between the preferred orientation of electrodeposited metals and the deposition overpotential. However, contrary to the above hypothesis, neither (001) nor (112) planes were preferentially oriented over high overpotential region. This seems to be caused by the change in the rate-determining step to the charge- to mass-transfer.(2) The mesoscopic structure of cobalt deposited from the chloride baths was quite different from the one from the sulfate baths. That is to say, the preferred (110) orientation was shown over significantly wide range of electrolysis conditions. This suggests that the structure of the intermediated formed during the electrodeposition process was changed by the presence of chloride ion.(3) Epitaxial relationship between the electrodeposited cobalt and the substrate was observed in the vicinity of their interface. The effect of the deposit thickness gradually diminished with increasing the amount of coulombs passed during electrolysis and the mesoscopic structure inherent to the electrolysis condition appeared(4) Chloride ions significantly affected the preferred orientation as well as the morphology of the deposits.(5) The morphology of the deposited cobalt was closely correlated with its preferred orientation.