Surface Enhanced Raman Scattering on a Single Nanometric Aperture

Arrays of nanoapertures have been demonstrated to realize efficient, robust, and reproducible substrates for surface-enhanced Raman scattering SERS spectroscopy. However, little attention has been devoted to single nanoapertures, although a thorough understanding of the SERS phenomenon in a single aperture is essential for the rationale optimization of nanoaperture arrays SERS. In this study, single nanoapertures milled in optically thick gold films are quantitatively evaluated for the first time to determine the SERS enhancement factors using para-mercaptoaniline as nonresonant analyte. We determine a peak enhancement factor of 2 x 10(5) for a single 100 nm diameter aperture. Although this is a moderate enhancement factor, we believe that nanoapertures deserve special attention to highlight the physical and chemical phenomena leading to SERS enhancement and better understand the design of nanoaperture arrays for SERS substrates. The experimental data are supported by numerical simulations and argue for a careful consideration of aperture diameter, incident polarization, analyte deposition method, and nature of the gold adhesion layer while designing aperture-based SERS substrates and evaluating SERS enhancement factors.