Charge‐transfer contributions in surface‐enhanced Raman scattering from Ag, Ag 2 S and Ag 2 Se substrates

The degree of charge‐transfer in Ag–4‐mercaptopyridine (Mpy) and Ag 2 S–4‐Mpy systems is investigated by use of surface‐enhanced Raman spectroscopy (SERS). Ag 2 S and Ag 2 Se nanoparticles are prepared on the basis of the former formation of Ag nanoparticles to make the SERS analytical objects comparable. We utilize the intensity of the non‐totally symmetric modes (either b 1 or b 2 ) as compared with the totally symmetric a 1 modes to measure the degree of charge‐transfer. We find ~25% of charge‐transfer contribution for Ag–4‐Mpy, whereas 81 ~ 93% for Ag 2 S–4‐Mpy. It means that the charge‐transfer resonance contribution dominates the overall enhancement in SERS of Ag 2 S–4‐Mpy. Energy level diagram is applied to discuss the likely charge‐transfer transition between Ag, Ag 2 S, Ag 2 Se and 4‐Mpy. This article may point out the link among the three main resonance sources and could enable some insights into the electronic pathways available to the metal‐molecule and semiconductor‐molecule systems. Copyright © 2012 John Wiley & Sons, Ltd.