Raman Spectroscopy of Molecular Monolayers in Inelastic Electron Tunneling Spectroscopy Junctions

Abstract

The intensity of Raman scattering from molecules in solution suggests that the observation of Raman scattering from molecular monolayers should be very difficult given the small number of molecules involved. However, recent experimental work on Raman scattering from molecules adsorbed on the surface of metal electrodes in electrochemical cells has shown that strong Raman scattering can be obtained from a monolayer of adsorbed molecules.^1,2,3 It has been estimated that the Raman cross section of a pyridine molecule adsorbed on an electrochemically prepared Ag surface in a KC1 solution is six orders of magnitude larger than for the same molecule in solution.² Although this large enhancement has stirred considerable experimental and theoretical interest, its microscopic origins remain unknown.^4,5,6