Hexagonally Patterned Silver Nanoparticles Electrodeposited on an Aluminum Plate for Surface-Enhanced Raman Scattering

We have fabricated hexagonally patterned silver nanoparticles for surface-enhanced Raman scattering (SERS) by electrodepositing silver on the surface of an aluminum plate prepared by completely removing the oxide, except for a thin bottom barrier layer, from anodic aluminum oxide (AAO) templates. Even after removing the oxide, well-ordered hexagonal patterns, similar to the shape of graphene, remained on the surface of the aluminum plate. The borders of the hexagonal pattern protruded up to form sorts of nanomountains at both the sides and apexes of the hexagon with the apexes protruding even more significantly than the sides. When silver was electro-deposited on the plate, silver nanoparticles were made along the hexagonal margins. Nanoparticles deposited around the apexes of the hexagonal pattern were larger than those made at the midpoints of the sides. Silver nanoparticles formed hexagonal nanopatterns and, as the average nanoparticle size increased with increasing electro-deposition time, they were almost in contact with each other. A good SERS spectrum was observed by excitation with a 514.5 nm laser line. The calculated enhancement factor was approximately 2 × 107, which is about 10 times higher than that measured from silver nanorods fabricated on an AAO template. This significant increase in enhancement factor may be the result of some junction effect between the silver nanoparticles made by this method. The high enhancement factor suggests that this substrate could be used to fabricate hot-spots for SERS.