Ultrashort, Angstrom-Scale Decay of Surface-Enhanced Raman Scattering at Hot Spots

Anisotropic plasmonic nanostructures are known to exhibit large enhancements of surface-enhanced Raman scattering (SERS) of adsorbed molecules at their sharp tips or edges, where the near-field is intense. We show that the SERS enhancement at such field hot spots decays over a distance of ca. 4 Å, much shorter than the typical decay length reported for SERS. The finding is made in SERS sensors constructed from chemically synthesized triangular nanoprisms with azobenzene reporter molecules linked to the nanoprism surface using variable chain length alkanethiol spacers. With the aid of electrodynamic simulations, the ultrashort decay length, the shortest reported to date, is explained by solely an electromagnetic field effect. Our work provides a key design consideration for the use of hot spots of anisotropic nanostructures for SERS. The angstrom-scale effect may also allow the achievement of intramolecular spatial resolution in SERS probing.