Rapidly fabrication of plasmonic structural color thin films through AAO process in an alkaline solution

Abstract

Metallic nanostructures can be designed using reflective color filters, also known as plasmonic structural color (PSC) material. Compared with nanoparticles, self-ordered nanoscale pores, and subwavelength gratings, plain metal–dielectric–metal (MDM) structures are inexpensive, simple to manufacture, and treated within a short period of time. In this study, a new silicate- and phosphate-containing alkaline electrolyte was used for the fast fabrication of PSC thin films using an anodic aluminum oxide (AAO) process. The full treatment time, including AAO treatment and deposition of the outer metal layer, was only a few minutes. The structural color in the visible region was simply controlled by adjusting the applied current density during anodization. The surface and cross-sectional morphologies of the formed AAO coatings were then examined through field emission scanning electron microscopy, while the element compositions were determined through energy-dispersive X-ray spectroscopy. The electrochemical impedance spectroscopy method was also employed to further clarify the coating characteristics. Next, the color performance was studied using a colorimeter and ultraviolet–visible spectrophotometer; the effects of outer-metallic-layer thickness and roughness on color shift and saturation were also investigated. The results contribute to our understanding of how inner dielectric-metal structures form, as well as how the corresponding surface plasmon resonance was influenced when current density was applied to an alkaline electrolyte. Notably, plain MDM structures appear to be suitable for reflective color filtering applications with low cost and fast fabrication.