Surface-Enhanced Raman Scattering (SERS) from Azobenzene Self-Assembled “Sandwiches”

A silver island film was thermally deposited on the top of an azobenzene self-assembled monolayer on gold, yielding a SERS-active system possessing a “sandwiched” structure of Ag|R 1 −Azo−R 2 S−|Au. For the first time, the positions of the Azo groups were controlled by using azobenzenealkanethiols with different terminal groups (R 1 ) or interchain spacers (R 2 ), to clarify the relationship between the SERS effect and the structural nature of the system. As will be shown, increases in distances of Azo groups from the gold substrate and from the silver film both cause the enhancement factor to decay exponentially, indicating that the enhancement correlates to both the gold substrate underneath and the silver islands above.