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Raman spectroelectrochemistry of molecules within individual electromagnetic hot spots

Timur Shegai (Institutionen för teknisk fysik, Bionanofotonik) ; Alexander Vaskevich ; Israel Rubinstein ; Gilad Haran
Journal of the American Chemical Society (00027863). Vol. 131 (2009), 40, p. 14392-14398.
[Artikel, refereegranskad vetenskaplig]

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.



Denna post skapades 2017-11-14.
CPL Pubid: 253128

 

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Institutioner (Chalmers)

Institutionen för teknisk fysik, Bionanofotonik (2007-2015)

Ämnesområden

Kemisk fysik
Kemiteknik

Chalmers infrastruktur