Surface Enhanced Raman Scattering from Lithographically Prepared Microstructures

Abstract

Observations of large (10⁶) enhancements of Raman cross sections for molecules adsorbed onto suitably roughened silver surfaces have generated much interest. The enhancement allows easy detection of submonolayer coverage of molecules on surfaces and presents the opportunity to obtain detailed information about molecules on surfaces by means of Raman spectroscopy. Recently many other optical processes such as second harmonic generation, dye luminescence and two-photon absorption have,also been shown to be enhanced on such silver surfaces. In this paper we discuss the mechanism for the enhancement and describe experiments which utilize surfaces having “controlled roughness”. These surfaces consist of arrays of isolated submicron silver particles which are uniform in shape and size. Modern techniaues of micro-lithography are used to produce these surfaces. With the help of these surfaces we are able to elucidate the mechanism responsible for Surface Enhanced Raman Scattering (SERS) and can design the surface for maximum enhancement. We have, to date, found¹ enhancements of 10⁷ on such surfaces.