Controlled Etching of Gold Seeds with Cysteamine: A Strategy for Realizing Arrays of Thin Substrate-Based Nanoplates

Abstract

The seed-mediated synthesis of gold nanoplates directly on substrate surfaces offers significant advantages over its seedless counterparts by allowing independent control over the nucleation and growth steps. It, however, remains an ongoing challenge to form monodisperse seeds with tunable dimensions that contain the symmetry-breaking stacking fault defects needed to promote planar growth. Current methods for seed formation exert control over their size, position, and crystallographic orientation relative to the substrate surface but are disadvantaged by size limitations that prevent the formation of nanoplates with thicknesses below 40 nm. Herein, a postfabrication strategy utilizing a cysteamine etchant is demonstrated to controllably reduce seed dimensions, facilitating the synthesis of high-yield nanoplates on substrate surfaces with thicknesses down to 15 nm. Integral to this strategy is the anisotropic etching of gold by cysteamine, as evidenced by comparisons to an isotropic etch, in situ spectroscopic monitoring of the etching process, discrete dipole approximation simulations, and first-principles density functional theory calculations. Using this capability, thin nanoplates are formed with plasmon resonances in the near-infrared and surface-enhanced Raman scattering signals that exceed those of thicker nanoplates. The work, hence, expands design possibilities for substrate-bound nanoplates and provides insights into the anisotropic etching of gold nanostructures.