Standing-Wave-Assisted Creation of Nanopillar Arrays with Vertically Integrated Nanogaps for SERS-Active Substrates

Abstract

An optical method is used to create multi-dimensional metal structures with three distinct periodicities for surface-enhanced Raman scattering (SERS). Periodic arrays of nanopillars are formed by phase-shift interference lithography on sub-micrometer length scales. With the help of a standing wave, each nanopillar is made to be a disk-stacking structure consisting of a series of 20-nm-thick metal nanogaps; the nanopillars consequently resemble a pagoda. The vertically integrated metal nanogaps of the metal-deposited pagoda-like nanopillars enable strong localization of an electromagnetic field and effective enhancement of Raman signals for molecules adsorbed on the metal surface. Moreover, the nanopillars are arranged in a regular lattice, which results in a low spatial variation of the SERS intensity and provides high reproducibility in measurements. Arrays of the nanopillars can be further micropatterned to have a periodicity ranging from tens of micrometers to a millimeter by subsequently employing photo-lithography. The nanopillar arrays promote the wetting of sample fluids, which enables the selective confinement of fluids on the array regions of the micropatterns without spreading. Consequently, numerous fluid samples can be separately deposited, enabling SERS-based analysis of multiple samples using a single substrate.