Self-assembled gold micro/nanostructure arrays based on superionic conductor RbAg₄I₅ films

Herein, we propose a new strategy to fabricate gold (Au) micro/nanostructure arrays by photocatalytic solid-state electrochemical reaction between superionic conductor RbAg₄I₅ and Au films. The Au and RbAg₄I₅ films were successively deposited on a clean quartz substrate by vacuum thermal deposition method. A copper microgrid possessing periodic holes 100 μm in diameter was put above the RbAg₄I₅ film as a mask plate, whereupon irradiation from a 405 nm wavelength laser was used to diffuse gold ions (Au⁺ ions) into vacant silver sites of RbAg₄I₅ and transfer Au⁺ through ion passageways in the RbAg₄I₅ film. When the laser was turned off, the Au⁺ ions were easily reduced due to low activity compared to the silver (Ag⁺) ions. After multiple on/off cycles of the 405 nm laser, the irradiated area of uniform Au film exhibited a periodic structural unit array whose period was the same as that of the mask plate hole array. Atomic force microscope and scanning electron microscope images revealed that a self-assembled needle-like nanostructure array grew perpendicular to the substrate surface inside each circle's structural unit. The height of the grown nanostructure array increased with laser power density. Raman enhancement of the gold nanostructure array as substrate was detected using Rhodamine 6G (R6G) ethanol solutions as probe molecules. The enhancement effect increased with the height of the grown nanostructure array, and could increase by two orders of magnitude greater than that of unirradiated Au film. This strategy offers a new method for the micro/nanostructure processing of gold and provides microscale-array-mediated surface-enhancement Raman-scattering (SERS) substrates comprising Au nanostructures for application in high-sensitivity spectrum analysis.