Synergetic light-harvesting and near-field enhancement in multi-scale patterned gold substrates

LUIS A. GUERRA HERNÁNDEZ, MARÍA ANTONIETA DAZA MILLONE, EMILIANO CORTÉS, MARCOS FEDERICO CASTEZ, BAPTISTE AUGUIE,, MARÍA E. VELA, ROBERTO C. SALVAREZZA, AND ALEJANDRO FAINSTEIN

ACS-Photonics

American Chemical Society

Año: 2015 vol. 2 p. 1355 - 1365

Sphere-segment void (SSV) cavities have emerged as promising substrates for reproducible Surface Enhanced Raman Scattering (SERS), offering strong and uniform electromagnetic enhancement associated with the excitation of cavity-like localized surface plasmon resonances tunable across the UV vis-near IR range, with a facile large-scale fabrication process. High-resolution electron micrographs of these structures reveal a considerable departure from the idealized smooth spherical cavity shape; notably, the electrochemical deposition of gold yields an important surface roughness. We investigate this contribution to the SERS activity of SSV substrates with a series of experiments, varying the degree of surface roughness using thermal annealing and gradual electrochemical roughening. Notably, we observe that both roughness features and cavity-like modes operate in conjunction as a multiscale antenna to provide larger SERS efficiency than the two mechanisms considered separately. We conclude that the main role of the ordered cavity structure is to increase the plasmonic mode density near rough surface features, thus, optimizing the coupling of far-field radiation (light harvesting) to locally enhanced near fields.