Experimental Verification of the SERS Electromagnetic Model beyond the |<i>E</i>|⁴ Approximation: Polarization Effects

Abstract

The failure of the so-called | E | 4 approximation of the surface-enhanced Raman scattering (SERS) electromagnetic (EM) enhancement factor is demonstrated experimentally using arrays of highly uniform gold nanoparticles specially designed for this purpose. This is first demonstrated for unpolarized detection, and the interpretation of the results then becomes evident by studying the case of polarized detection. These results provide, at the same time, a clear experimental verification of the generalized EM theory of SERS beyond the | E | 4 approximation ( Chem. Phys. Lett. 2006, 423, 63). A nontrivial consequence of these concepts is the almost complete polarization rotation of the SERS signal with respect to the incident polarization. This occurs for a prolate nanoparticle with plasmon resonances peaking on either side of the main spectral range covered by the Raman spectrum of the probe. Finally, we discuss how such experiments can be used to extract some information about the molecular adsorption orientation of the probe.