| In Chapter 1 an accurate but simple method for determining electromagnetic fields near the surfaces of small metal spheroidal particles is developed and in Chapter 2 it is used to determine field and Raman enhancements for 10 metals in Groups 1, 11, 12 and 13. This method corrects the simple small particle LaPlace electrostatic field for electrodynamic depolarization and damping effects to give a result which is equivalent to solving Maxwell's equations to order k;In Chapter 3 we present a theoretical study of the coverage and frequency dependence of surface (enhanced) resonance Raman scattering (S(E)RRS) of cobalt phthalocyanine (CoPc) on rough silver. Experimental spectra for this system indicate a rather strong coverage dependence at very low coverage for excitation at or close to the molecular resonance frequency, with a peak at 0.07 monolayer (ML) followed by a rapid decrease above that. To model this coverage dependence, we consider the electromagnetic interactions between the adsorbate and substrate, with the substrate modeled as a metal spheroid and the adsorbate as (1) an effective medium having a coverage dependent dielectric constant, and (2) a random distribution of polarizable dipoles which are coupled to each other and to the metal particle. It is found that although there are differences between the two models, the coverage dependence for reasonably prolate spheroids is similar in both, with peak intensities at about 0.1 ML and a drop in intensity above 0.1 ML arising from damping of the plasmon resonance by the adsorbed layer. |
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