Darling-Dennison resonance of thiourea adsorbed on the silver electrode revealed by surface enhanced Raman spectroscopy

Abstract

We report surface enhanced Raman spectroscopy (SERS) of Darling-Dennison resonance of thiourea on Ag electrode excited at 514.5 nm laser excitation. Darling-Dennison resonance indicates that two degenerate Raman modes interact with each other and their degenerate first-order overtone modes obtain energy and appear in Raman spectra. Our study showed that the ratio of intensity of the Darling-Dennison resonance is up to 0.24 of its fundamental Raman intensity, when the applied electrode voltage is at -0.4 V versus the saturated calomel electrode. This phenomenon was also observed on the Ag island film surface at ambient condition. These observations demonstrated strong evidence for Darling-Dennison resonance band in SERS. The implications of these observations are also discussed. Copyright © 2013 John Wiley & Sons, Ltd. Darling-Dennison resonance indicates that two degenerate Raman modes interact with each other and their degenerate first-order overtone modes obtain energy and appear in Raman spectra. The surface-enhanced Raman spectroscopy (SERS) of thiourea on Ag electrode excited at 514.5 nm laser excitation was obtained, and the combinational modes, which attributed to Darling-Dennison resonance, were observed in SERS on electrode and on silver island film, respectively, because of strong anharmonicity. Copyright © 2013 John Wiley & Sons, Ltd.