文摘
Nanoaperture arrays in a silver film were quantitatively evaluated, for the first time, to determine the absoluteRaman 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 anaverage area-corrected SERS enhancement factor of (6 ± 3) × 107 for 514.5 nm excitation. Comparisonbetween theory and experiment provided critical insight into the magnitude and origin of enhancement inthese nanoaperture arrays as a function of lattice spacing. The measured enhancement factor was attributedto two distinct sources: a factor of 105 from nm scale roughness associated with the Ag film in the absenceof the nanoapertures and a factor of 6 × 102 associated with plasmons localized near the aperture edges.