電極表面上の吸着界面活性剤の相転移に誘起される振動電析反応と合金多層膜の形成

抄録

The electrodeposition reaction in an acidic solution containing Cu²⁺ and Sn²⁺ shows, in the presence of a cationic surfactant, a negative differential resistance (NDR) and a current oscillation in a potential region where SnCu alloy is deposited. Depth profiles obtained by Auger electron spectroscopy (AES) have indicated that alloy films deposited during the oscillation have a structure of nano-period multilayers composed of alloys of different compositions. Detailed investigations have revealed that the NDR arises from adsorption of a cationic surfactant (acting as an inhibitor for diffusion of Cu²⁺ and Sn²⁺ ions) on the electrode (alloy) surface and the oscillation comes from coupling of the NDR with the ohmic drop in the electrolyte. A notable point is that the NDR appears in a very narrow region of the potential (of about 5 mV or less). This fact strongly suggests that the NDR (and the oscillation) arise from a sudden structural change in an adsorbed surfactant layer such as a phase transition from a gaseous adsorbed layer to a condensed liquid-like one. This conclusion was supported by the experiments on effects of the concentration and the chain length of the surfactant on the NDR.