Quantitative evaluation of plasmon enhanced Raman scattering from nanoaperture arrays

Nanoaperture arrays in a silver film were quantitatively evaluated, for the first time, to determine the absolute Raman scattering enhancement factors as a function of aperture lattice spacing using a nonresonant analyte. The arrays, with 200 nm diameter apertures and varying spacing in a 50 nm thick silver film, resulted in an average area-corrected SERS enhancement factor of (6 +/- 3) x 10(7) for 514.5 nm excitation. Comparison between theory and experiment provided critical insight into the magnitude and origin of enhancement in these nanoaperture arrays as a function of lattice spacing. The measured enhancement factor was attributed to two distinct sources: a factor of 10(5) from nm scale roughness associated with the Ag film in the absence of the nanoapertures and a factor of 6 x 10(2) associated with plasmons localized near the aperture edges.