Nanopillars array for surface enhanced Raman scattering

We present a new class of surface-enhanced Raman scattering (SERS) substrates based on lithographically-defined two-dimensional rectangular array of nanopillars. Two types of nanopillars within this class are discussed: vertical pillars and tapered pillars. For the vertical pillars, the gap between each pair of nanopillars is small enough (< 50 nm) such that highly confined plasmonic cavity resonances are supported between the pillars when light is incident upon them, and the anti-nodes of these resonances act as three-dimensional hotspots for SERS. For the tapered pillars, SERS enhancement arises from the nanofocusing effect due to the sharp tip on top. SERS experiments were carried out on these substrates using various concentrations of 1,2 bis-(4-pyridyl)-ethylene (BPE), benzenethiol (BT) monolayer and toluene vapor. The results show that SERS enhancement factor of over 0.5 x 10(9) can be achieved, and BPE can be detected down to femto-molar concentration level. The results also show promising potential for the use of these substrates in environmental monitoring of gases and vapors such as volatile organic compounds.