Chemical adsorption on a metal surface involves hybridization between localized electronic states of the adsorbed molecule and the extended bands of the metal. As a result, the electronic properties of both the metal and the adsorbate are changed. This project uses a combination of electrical resistance and infrared reflectance measurements on carefully prepared thin metal films to explore important aspects of both effects. Adsorbate effects on the electrical resistance of thin metal films are usually attributed to scattering of conduction electrons from the adsorbates. A specific prediction of this model - that the ratio of the reflectance change to resistivity change should be independent of the adsorbate - has been shown to be violated, indicating that other processes are involved. The present research extends that work by exploring the effects of different adsorbates, temperature and substrate modifications in order to clarify the actual mechanisms of surface resistivity. Modification of the adsorbate's properties depends on the electronic structure of the metal, and is sensitively reflected in the adsorbate's vibrational spectrum. Metallic quantum wells provide a means of reproducibly and continuously modifying the electronic structure near the Fermi level. Adsorption of CO on Cu/Co quantum wells will be studied in order to investigate the effects of the electronic structure modification on the vibrational frequency and line width and on broadband reflectance changes. %%% As solid structures are made ever smaller, the effects of surface contaminants become increasingly important. When a metal film is about one hundred atomic layers thick, for example, a single layer of molecules on its surface can change its resistance to the flow of electricity by more than ten per cent. Such effects can be exploited to develop sensors for chemicals. They can also be detrimental, increasing heating and slowing transmission speeds in microcircuits. This research aims to understand the mechanisms underlying these resistance changes. The prevailing theory attributes these changes to scattering of the electrons in the metal by the molecules, much as dust on a mirror scatters light, but some predictions of this theory are not in agreement with the observed facts. This research is directed toward the measurements of the surface resistance of metal films under the influence of incident infrared light in order to provide critical data to resolve this discrepancy and to help clarify the understanding of effects of surface molecules on the flow of electric current. This research will engage graduate students and post doctoral research associates who thereby receive training a forefront area of condensed matter physics and materials science and prepare them for employment in technological areas during the next few decades of the 21st Century.
