Tailoring Plasmonic Fields with Shape-Controlled Single-Crystal Gold Metasurfaces

Geometry and crystallinity play a critical role in the wavelength-dependent optical responses and plasmonic local near-field distributions of metallic nanostructures. Nevertheless, the ability to tailor the shape and position of crystalline metal surface nanostructures has remained a challenge that limits control of their enhanced local fields and represents a barrier to harnessing their individual and collective responses. Here, we describe a solution deposition method in the presence of anionic additives, which yields shape-controlled, single-crystal plasmonic gold nanostructures on Ag(100) and Au(100) substrates. Use of SO₄^2- ions yields smooth Au(111)-faceted square pyramids with large plasmonic Raman enhancements. Halide additives produce textured hillocks comprising edge- and screw-type dislocations (Cl^-), or platelets with large-area Au(100) terraces and (110) step edges (Br^-), while SO₄^2- and Br^- additive combinations provide Au(110)-faceted square pyramids. With lithographic patterning, this chemistry yields metal deposition with precise geometry and location control to provide single-crystal, plasmonic gold metasurfaces with tailored optical response. The appropriately designed metasurfaces can then generate large Raman scattering enhancements, far greater than high density gold square pyramids with random surface disposition. Shape-controlled single-crystal plasmonic metasurfaces will thus offer opportunities to tune the characteristics of nanostructures, providing enhanced optical, photocatalytic, and sensory response.