Controlled Etching as a Route to High Quality Silver Nanospheres for Optical Studies

We present a new method based on wet etching for the production of high quality, single-crystal Ag nanospheres. By rapidly mixing a suspension of uniform Ag nanocubes with a small amount of ferric nitrate or ferricyanide-based etching solution, we could either truncate the sharp corners and edges to form rounded nanocubes or etch further to obtain nanospheres without sharp features but with roughly the same diameter as the original cubes. Notably, this technique could be used to produce uniform Ag nanospheres with a broad range of sizes, opening up new possibilities for fundamental studies on surface-enhanced Raman scattering (SERS), as previous synthetic methods were unable to produce uniform spheres larger than ∼35 nm. In this paper, we demonstrate the synthesis of Ag spheres as small as 25 nm and as large as 142 nm and investigate their SERS properties, finding the 142 nm spheres to have an order of magnitude larger enhancement factor. We also used these nanocrystals to study the effect of sharp corners and edges on the localized surface plasmon resonance.