Electrochemical deposition of stacked layers of Cu2O/Cu/Cu2O and rendering of structural colors

Cu2O is a transparent solid with a red color and has a very high refractive index (n similar to 3). Electrochemical reduction of copper-lactate complex from aqueous alkaline solution containing copper, sulfuric, and lactic ions produces thin films of metallic copper and Cu2O on the electrode. The oxidation state (metallic copper or Cu2O) and the thickness of the film can be controlled by the electrode potential and the charge. Stacking of Cu2O and metallic copper films is possible from the same solution using organic additives. We tried to electrodeposit the stacked layers of Cu2O and metallic copper by applying stepping potential in order to render the structural color, which is much like the structure of a dielectric multilayer mirror. The reflective spectra of the stacked film obtained show interference fringes in the transparent region of > similar to 450 nm, and they shift according to changes of the incident angle. As a result, the various structural colors can be rendered for the films deposited by consecutive electrochemical deposition of Cu2O and Cu from the same solution.