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Wavelength-Scanned Surface-Enhanced Raman Excitation

 Spectroscopy on Well-Defined Silver Nanoparticle Arrays

Presented by Matt Young of Northwestern University

                                                                                                                        This work presents the most thorough wavelength-scanned excitation spectroscopy study to date.  Ag nanoparticles, fabricated using nanosphere lithography, are used as substrates, providing extremely well-characterized and size-homogenous nanoparticle arrays.  Surface-enhanced Raman scattering (SERS) intensities of adsorbed benzenethiol monolayers are correlated to the localized surface plasmon resonance (LSPR) of the nanoparticle arrays.  SER spectra are taken using excitation wavelengths from 425-800 nm and a triple spectrograph.  The SER excitation spectra are shown to have similar line shapes to the LSPR spectra.  In addition, the maximum SERS enhancement is shown to occur for wavelengths slightly shorter than the excitation wavelength such that both the incident photon and the Raman scattered photon are strongly enhanced.  Three different Raman peaks of benzenethiol are studied simultaneously on one substrate and it is shown that the smaller Raman shifted peak shows a maximum enhancement closer to the LSPR λ max than that of a larger Raman shifted peak.  This is in qualitative agreement with what is predicted by the electromagnetic enhancement mechanism.  Enhancement factors of up to 1 x 108 are achieved, which is in good agreement with previous SERS studies done on these substrates.