Surface-enhanced second-harmonic generation and Raman scattering

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Abstract
Emission from a variety of surface optical processes is significantly incrased at interfaces with roughened noble metals. A general formalism, applicable to any optical process, is used to predict the enhancement in the radiated power for second-harmonic generation and Raman scattering from an electrochemically reformed silver surface. Experimental results for these enhancements at different wavelengths are reported. The intensity of the second-harmonic radiation can be understood strictly in terms of the strong macroscopic electric fields produced at the roughened surface by resonant structures. For Raman scattering, part of the enhancement also arises from microscopic local-field effects and the direct chemical interaction of the adsorbate and substrate. The surface-enhanced second-harmonic and Raman signals are studied as the silver sample undergoes oxidation and reduction in an electrolyte containing cyanide ions. The behavior of these two easily measurable probes is described and correlated with the system's surface chemistry.