title: Alkyl-Nitrile Adlayers as Probes of Plasmonically Induced Electric Fields.
abstract: Vibrational Stark shifts observed from mercaptoalkyl monolayers on surface enhanced Raman (SERS) active materials are reported to provide a direct measurement of the local electric field around plasmonic nanostructures. Adlayers of CN-, p-mercaptobenzonitrile, and n-mercaptobutylnitrile were adsorbed to a heterogeneous nanostructured Ag surface. The frequency of the CN moiety was observed to shift in a correlated fashion with the SERS intensity. These shifts are attributed to a vibrational Stark shift arising from rectification of the optical field, which gives rise to a DC potential on the surface. All three molecules showed CN Stark shifts on the plasmonic surfaces. P-mercaptobenzonitrile is observed to be a well-behaved probe of the electric field, providing a narrow spectral line, suggesting a more uniform orientation on the surface. The utility of p-mercaptobenzonitrile was demonstrated by successfully assessing the electric field between gold nanoparticles adsorbed to a monolayer of the nitrile on a flat gold surface. A model is presented where the Stark shift of the alkyl-nitrile probe can be correlated to optical field, providing an intensity independent measurement of the local electric field environment.
authors.affiliation: Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA.
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Kwasnieski
authors.affiliation: Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA.
authors.forename: Hao
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA.
authors.forename: Zachary D
authors.initials: ZD
authors.lastname: Schultz