Raman spectroelectrochemistry of molecules within individual electromagnetic hot spots
Artikel i vetenskaplig tidskrift, 2009

The role of chemical enhancement in surface-enhanced Raman scattering (SERS) remains a contested subject. We study SERS spectra of 4-mercaptopyridine molecules excited far from the molecular resonance, which are collected from individual electromagnetic hot spots at concentrations close to the single-molecule limit. The hot spots are created by depositing Tollen's silver island films on a transparent electrode incorporated within an electrochemical cell. Analysis of the intensity of the spectra relative to those obtained from individual rhodamine 6G molecules on the same surface provides a lower limit of ?3 orders of magnitude for the chemical enhancement. This large enhancement is likely to be due to a charge transfer resonance involving the transfer of an electron from the metal to an adsorbed molecule. Excitation at three different wavelengths, as well as variation of electrode potential from 0 to -1.2 V, lead to significant changes in the relative intensities of bands in the spectrum. It is suggested that while the bulk of the enhancement is due to an Albrecht A-term resonance Raman effect (involving the charge transfer transition), vibronic coupling provides additional enhancement which is sensitive to electrode potential. The measurement of potential-dependent SERS spectra from individual hot spots opens the way to a thorough characterization of chemical enhancement, as well to studies of redox phenomena at the single-molecule level.

Författare

Timur Shegai

Chalmers, Teknisk fysik, Bionanofotonik

Alexander Vaskevich

Weizmann Institute of Science

Israel Rubinstein

Weizmann Institute of Science

Gilad Haran

Weizmann Institute of Science

Journal of the American Chemical Society

0002-7863 (ISSN) 1520-5126 (eISSN)

Vol. 131 14392-14398

Ämneskategorier

Kemiteknik

Atom- och molekylfysik och optik

DOI

10.1021/ja904480r