Masters Theses

Date of Award

8-1991

Degree Type

Thesis

Degree Name

Master of Science

Major

Physics

Major Professor

Thomas L. Ferrell

Committee Members

R. J. Warmack, J. O. Thomson

Abstract

Pyridine is a well characterized standard for studying surface-enhanced Raman scattering (SERS), and its adsorption from solution onto silver metal has been thoroughly investigated. However, pyridine evaporates very quickly in air from the surface of silver metal at room temperature, so vapor-phase experiments have had to be performed at cryogenic temperatures. This thesis describes studies of the effects of materials which may assist adsorption of molecules such as pyridine on a silver metal surface at room temperature. Additionally, the reported work assesses the effects of contaminants on the SERS signal. Gold, carbon, and carbon monoxide were tested in order to determine if they assist adsorption on silver, or simply act as contaminants. Experiments were conducted in steady state vapor studies, surface deterioration, and open-system desorption using standard silver substrates and gold-coated silver substrates. An additional set of experiments was performed for toluene using similar silver substrates and gold-coated silver substrates. The results of steady state vapor studies for pyridine show that there is no strong effect of laser power on adsorption/desorption at 70 mW for both the silver substrate and gold-coated silver substrate. It also appears that gold may tend to adsorb pyridine molecules slightly more strongly than does silver. The results for toluene show irregular changes because of the relatively weak intensity of the signal. In some cases we observed substrate deterioration with time. There is a similarity of the deterioration curve (normalized SERS intensity) between the silver substrates and gold-coated substrates for both pyridine and toluene. The results of open-system desorption were expected to show the difference between the effects at ambient temperature and at 50 °C. Contrary to expectation, no significant difference of this type was seen. The results for toluene were inconclusive because of high-noise levels and a weak SERS signal intensity. The results of carbon monoxide gas mixed with pyridine vapor showed a slightly faster drop of signal intensity than the results for pyridine vapor alone. However, both are fairly similar. The results for carbon-coated silver substrates mostly showed high background in the spectra. It was hard to see clearly any adsorbing effect because of the presence of a high noise background. The results do show that 6-nm carbon data is the most stable in terms of signal strength over a period of time.

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