SERS Study Of Silver Nano-structure Arrays Of Different Diameter Fabricated By Anodic Aluminum Oxide

Surface enhanced Raman scattering (SERS) is an ultra-sensitive spectroscopy to study surface adsorption and trace analysis. Silver substrate with surface nano-structure arrays is SERS active and usually prepared with a template.Recently, anodic aluminum oxide (AAO) is a kind of promising template with arising attention. AAO can be described as a closed-packed array of hexagonally arranged cells containing pores in each cell center. During the process of anodization of aluminum, periodic concave hexagonal pattern was formed on aluminum base after the first anodization. The size of the aluminum cell is as large as that of the AAO cell under the same anodizing potential. By manipulating the anodizing potential, hexagonal cell of different size are obtained on AAO and aluminum base. Therefore,when we set the anodizing voltage at 30V,40V and 50V, aluminum base with different cell diameter, respectively about 80nm, 100nm and 120nm, were obtained.The three kinds of obtained aluminum bases were sputtered with a silver layer of 200nm. After the removal of aluminum bases, three different silver layers with nanostructure arrays of such diameters as 65nm, 85nm and 105nm were obtained. Since the silver layer is covered and consequently protected by the aluminum base, the silver layer can be stored for months before used. From the AFM images, we found that the convex pattern on silver layers matched the concave pattern on corresponding aluminum base. Besides, when the diameter of the nanostructure on silver layer equaled to 105nm, the convex on silver layer was much like a hexagonal prism instead of a spherical cap observed on the other two kinds of silver layer. In addition, the three silver layers possessed different SERS enhance ability. The best enhanced SERS appeared on the silver substrate with spherical caps of 85nm. Finally, reproducible signals were detected on all of the three substrates due to their uniform nano structure.Although the substrate with 85nm-spherical-cap arrays could best enhanced SERS signals among the three substrates, its enhance ability was lower than that of the traditional silver colloid. To solve the problem, we grew silver again by immersing the 85nm-silver-spherical-cap arrays in a silver enhancer kit. As the immersing time added, the SERS enhance ability improved. When the immersing time equaled to 210 seconds, the silver substrate showed a highest SERS signal.