Localization of image state electrons in the sulfur headgroup region of alkanethiol self-assembled films

experimental observation of electronic Raman scattering between image potential surface states is described and has been observed from roughened Au and Ag surfaces covered with long-chain alkanethiol self-assembled monolayers. To simulate the effect of surface roughness, interactions of the image state electron are modeled using a potential that incorporates two orthogonal metal surface planes, as would be expected near a step edge. Although the Raman spectra indicate that the image state electron exists within the film, modeling suggests more specifically that the electron is constrained to move within the sulfur headgroup layer. Although it is commonly accepted that the headgroup binding and structure on these surfaces is identical for both the short and the long chain alkanethiol homologues, these results highlight dramatic differences in the Au/S interfacial electronic structure between these two chain length regimes at room temperature.