Ellipsometric Spectroscopy Study of Anodically Formed Silver (I) Oxide Films on Silver

摘要

Spectroscopic ellipsometry has been used in combination with electrochemical measurements to determine details of the nucleation process of silver oxide anodically formed on silver in 1M KOH solutions. Spectroscopic ellipsometry is shown to be sufficiently sensitive to determine parameters pertaining to the growth rate and morphology of crystalline oxide films. The anodic film starts as a submonolayer and then grows into a uniform multilayer. At potential below a nucleation potential (approximately 200 mV versus Ag/AgCl 4M KCl), current efficiencies for film growth are small, because most of the oxidized material dissolves. When a certain degree of supersaturation is reached (23X saturation), a crystalline oxide is nucleated. The crystals grow, in part, by the transfer of oxide from the uniform multilayer with the rate of oxide growth controlled by the rate of incorporation of dissolved material at the crystal/solution interface. Due to the high solubility of small nuclei, a transfer of material from smaller to larger crystals occurs in the early stages of crystal growth. A theoretical model of a dissolution/precipitation process is presented for the current response to an applied potential step. (ERA citation 11:020588)