Inverted size-dependence of surface-enhanced Raman scattering on gold nanohole and nanodisk arrays.

Surface-enhanced Raman scattering (SERS) on gold nanohole and nanodisk arrays with precisely controlled size and spacing fabricated via electron beam lithography was investigated. These nanostructures exhibit strong SERS signals at 785 nm excitation but not at 514 nm. When the edge-to-edge distance is maintained, enhancement increases for nanoholes but decreases for nanodisks as diameter is increased. It is shown that the observed enhancement results from the local surface plasmon resonance wavelength shifts to the near-infrared regime as nanohole diameter increases. The large tolerance on dimensions and the empty space confined by nanoholes suggest promise for their use as a functional component in sensing, spectroscopy, and photonic devices.