Fabrication and optical characterization of silver-coated gradient-grown anodic aluminum oxide

Here, we introduce gradient-grown anodic aluminum oxides (G-AAO) produced using a gear-train with a ratio of 1:16 and controlling the drawing velocity during a 2nd anodization period (t_2A). After silver (Ag) deposition on G-AAOs, their optical behaviors are investigated as an interference-plasmonic coupling effect. First, we examine the geometrical and optical characteristics of statically grown AAO (S-AAO) on which 20 nm thick Ag is deposited. An obvious color change is found from blue (t_2A = 30 s) to red (t_2A = 90 s) due to an interference-plasmonic coupling. Second, we fabricate G-AAOs using a dynamic 2nd anodization with two different drawing velocities of 1.1 mm s⁻¹ and 2.2 mm s⁻¹. As a result, a linear increase in thickness (about 1.23 nm s⁻¹) is found in G-AAOs. After Ag deposition, a clear color change is not found but an optical red shift in absorption is observed on Ag-coated G-AAOs. Thus, our results provide the first constraints on optical behavior of a metal-coated G-AAO, with a variety of nano-optical applications.