Comparative Study of Plasmonic Resonances between the Roundest and Randomly Faceted Au Nanoparticles-on-Mirror Cavities

Over the past decade, the synthesis of a relatively large-sized (>50 nm), spherical gold nanoparticles (Au NPs) has undergone significant progress, from the initial demonstration of the hydroquinone-mediated synthesis of randomly faceted Au nanospheres (NSs) to iterative growth and dissolution of highly spherical and ultrasmooth Au NSs. The iterative growth and dissolution method can synthesize the roundest Au NSs. However, the roundest Au NSs have not been used in nanoparticle-on-mirror (NPoM) cavities; thus, the effects of Au NS roundness and facets on the plasmonic resonance of an NPoM cavity needs to be understood. In this work, we synthesized the Au NSs of the same size but with different facets and used them in NPoM cavities. Using these plasmonic models, we systematically compared round and randomly faceted Au NSs in terms of plasmonic resonance and spectral reliability. On the basis of these experimental results, we theoretically defined the accessible plasmonic mode volume with an NPoM cavity.