Surface enhanced Ramam scattering studies in ultrahigh vacuum
Wood, Thomas Huntington
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https://hdl.handle.net/2142/25529
Description
Title
Surface enhanced Ramam scattering studies in ultrahigh vacuum
Author(s)
Wood, Thomas Huntington
Issue Date
1980
Doctoral Committee Chair(s)
Klein, Miles V.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
surface enhanced Raman scattering
Raman scattering
ultrahigh vacuum
carbon monoxide adsorbed on silver films
Language
en
Abstract
We have observed Raman scattering signals from carbon monoxide adsorbed on silver films deposited on a 120 K substrate that are approximately 5 orders of magnitude stronger than would be expected from the known cross section. These studies were performed in an ultrahigh vacuum chamber. This enhancement is similar to that observed off silver electroue5 in electrochemical cells. The enhancement is destroyed by room temperature annealing of bur films, so we infer that the surface roughness inherent in our evaporation process is essential to the enhancement mechanism. This, along with the fact that enhancement is observed for such a weakly bound system, suggests that many of the proposed mechanisms of Raman enhancement do not properly describe the observed phenomena.
We have also observed enhanced Raman scattering from CO adsorbed on evaporated gold films, although the enhancement is approximately 300 times weaker than it is for silver. The dependence of the enhanced signals on laser wavelength for CO adsorbed on silver and gold was studied. For silver, the enhancemen was stronger at the blue end of the spectrum than at the red end, and the opposite result was found for gold. The result for silver is contrary to results obtained by several other groups in elcctrochemical cells.
Single crystal silver (Ill) films grown epitaxially on mica in situ and polycrystalline aluminum films deposited on cooled substrates both showed bands at 1360 and 1590 cm-1 before intentional exposure to adsorbates. The origin of these bands was not firmly established.
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