Coverage dependence of Raman scattering from pyridine adsorbed to silver/vacuum interfaces

Abstract Raman spectra from pyridine adsorbed to silver films evaporated on cooled substrates under UHV conditions have been investigated in the exposure range 3×10 −2 L to 10 3 L. Surface enhanced Raman signals have been detected even for the smallest exposure and reached a maximum in intensity at about monolayer coverage. Extended exposure to pyridine exceeding monolayer coverage results in a variation of the Raman spectrum eventually leading to additional Raman peaks due to ordinary scattering from thick condensed pyridine layers. Several further observations make an explanation of surface enhanced Raman scattering on the basis of electromagnetic resonances unlikely.

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