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Surface Enhanced Raman Scattering, often abbreviated as SERS, is the enhancement of Raman scattering by molecules adsorbed on rough metal surfaces. For electrochemically roughened silver films the enhancement factor can be as large as 1014; this enables Surface Enhanced Raman Spectroscopy (which also is abbreviated SERS) to be a sensitive technique.

[edit] History

SERS from pyridine adsorbed on electochemically roughened silver was produced by Martin Fleischman and coworkers in 1974; they did not remark that the amount of Raman scattering was unexpectedly large. [1]. A few years later, two groups reproduced the effect, and pointed out that the amount of Raman scattering was far greater than expected. [2] [3]

For a while this effect was also called Giant Raman Scattering. A flurry of experimentation revealed that the Raman effect for molecules is greatly enhanced when they are adsorbed onto rough silver or gold surfaces. In some cases other metals may be used, but with less enhancement. Such rough surfaces can be created electrochemically, by deposition in vacuum onto liquid nitrogen cooled substrates, by depostion as metal island films, or by the clumping of sols.


[edit] Current status

It is now generally believed that SERS is caused by surface plasmon resonance. The enhancement of the Raman signal is due to a local electromagnetic field enhancement provided by optically active nanoparticles. Because the theoretically predicted enhancements fall short of the experimental results, another mechanism, called chemical enhancement, was proposed. The chemical enhancement is from a charge transfer complex or bond formation of the metal and adsorbate which increases the molecular polarizability.

In the early days of SERS, there was no consensus about the mechanism, and there still appear to be papers published in the literature in which the authors themselves are rather confused about what is going on. Current understanding suggests that the enhanced optical activity results from the excitation of local surface plasmon modes that are excited by focusing laser light onto the nanoparticle.

SERS gives all the information usually found in Raman spectra; it is a sensitive vibrational spectroscopy that gives structural information on the molecule and its local interactions.

[edit] Notes

  1. ^ Fleischmann, M.; PJ Hendra and AJ McQuillan (15 May 1974). "Raman Spectra of Pyridine Adsorbed at a Silver Electrode". Chemical Physics Letters 26 (2): 163-166. 
  2. ^ Albrecht, M. Grant; J. Alan Creighton (1977). "Anomalously Intense Raman Spectra of Pyridine at a Silver Electrode". Journal of the American Chemical Society 99: 5215-5219. 
  3. ^ Jeanmaire, David L.; Richard P. van Duyne (1977). "Surface Raman Electrochemistry Part I. Heterocyclic, Aromatic and Aliphatic Amines Adsorbed on the Anodized Silver Electrode". Journal of Electroanalytical Chemistry 84: 1-20. Elsevier Sequouia S.A.. 

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