Large-scale fabrication of nanodimple arrays for surface-enhanced Raman scattering.

ABSTRACT

Here we report a simple bottom-up technology for scalably fabricating gold nanodimple arrays with tunable nanostructures for surface-enhanced Raman scattering (SERS). Double-layer silica colloidal crystal-polymer nanocomposites with an unusual non-close-packed structure created using a spin-coating technique are utilized as structural templates. A variety of nanodimple structures, including simple monolayer voids, nanoring-like nanodimples, and binary-void nanodimples, can be reproducibly templated over wafer-sized areas by simply controlling the conditions during an oxygen plasma etching process. Normal-incidence specular reflection measurements show that the resulting gold nanodimple arrays exhibit tunable surface plasmon properties. The efficient electromagnetic coupling between neighboring nanodimples and inner-outer walls of nanoring-like nanodimples leads to high SERS enhancement factors (>10(8)). Numerical simulations based on a finite-difference time-domain model complement the experimental measurements, showing the spatial distribution of electromagnetic "hot spots" surrounding the periodic gold nanodimple arrays.