Silver-coated flower-like ZnO nanorod arrays: Ultrastable SERS substrates and the mechanisms of optical stability

The optical stability of silver-coated flower-like ZnO nanorod (NR) arrays were studied in terms of localized surface plasmon resonance and surface-enhanced Raman spectroscopy (SERS). As a highly sensitive SERS substrate, the silver-coated ZnO NR arrays enabled as low as 10(-14) M Rhodamine-6G (R6G) molecules to be detected and exhibited a long-term optical stability with a shelf life longer than two years. Using specially prepared samples, the Ag-ZnO nanostructures were studied as a metal-semiconductor junction and the importance of electron transfer between the silver and ZnO NRs for optical stability of silver in the SERS substrates was demonstrated. By addressing the growth behavior of silver in different samples, the good crystallinity of silver was suggested to be another crucial factor of maintaining the SERS activity long-term stable.