Surface enhanced Raman scattering of pyridine on different silver surfaces

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Abstract
Ultra high vacuum (UHV) experiments have been carried out in which different types of Ag substrates are prepared side‐by‐side in situ. One of the Ag substrates in a thin island film formed by depositing Ag on heated substrate. The other is prepared be depositing a thicker continuous film onto a cooled substrate. By depositing the pyridine simultaneously on the different Ag surfaces a direct comparison of the surface enhanced Raman scattering (SERS) behavior on these different Ag substrates have been made. The results indicate that some of the significant differences in the spectral features of the SERS phenomenon such as peak positions and relative intensity of the various vibrational modes observed by various laboratories for pyridine molecules condensed on Ag substrates are real. The differences involve microscopic features of the surface morphology and cannot be easily explained in terms of classical electromagnetic theory alone. It is proposed that there is a variety of ’’active sites’’ that can be formed on the Ag surface to which a pyridine molecule can be attached giving rise to a characteristic SERS behavior for that site. The density distribution of the various active sites on the surface of an Ag substrate varies depending on its preparation and its history.