Regular papers

Nanostructure design for surface-enhanced Raman spectroscopy – prospects and limits

¹ Department of Photonics Engineering, Technical University of Denmark, DTU Fotonik, DTU-building 345 west, DK-2800 Kongens Lyngby
² Department of Micro and Nanotechnology, Technical University of Denmark, DTU Nanotech, DTU-building 345 east, DK-2800 Kongens Lyngby, Denmark
³ Laboratory of Physics, Helsinki University of Technology, P. O. Box 1100, FI-02015 HUT, Finland

^* asger@mailaps.org

Received: 30 April 2008

Abstract

Surface-enhanced Raman spectroscopy (SERS) allows single-molecule detection due to the strong field localization occurring at sharp bends or kinks of the metal-vacuum interface. An important question concerns the limits of the signal enhancement that can be achieved via a judicious design of the surface. By using a specific example of a technologically realizable nanopatterned surface, we demonstrate that while very high enhancement factors (≈ 10¹²) can be found for an ideal surface, these are unlikely to be achieved in laboratory samples, because even a minute, inevitable rounding-off strongly suppresses the enhancement, as well as shifts the optimal frequency. Our simulations indicate that the geometric enhancement factors are unlikely to exceed ≈ 10⁸ for real samples, and that it is necessary to consider the geometric uncertainty to reliably predict the frequency for maximum enhancement.