Surface Plasmon and the Effect of Coupled Resonances in the Enhancement of Phonon and Molecular Modes in Semiconductors

The presence of surface plasmon resonance in semiconductors is not a typical point of discussion in the research community. While the presence of surface plasmon resonance in metals is widely accepted due to the presence of free electrons in conduction bands, the existence of surface plasmon in semiconductors has been generally ruled out due to the absence of free electrons in conduction bands. In this dissertation, we show that semiconductors are able to support surface plasmon in valence band. We also demonstrate, by using the Mie theory, that semiconductor nanoparticles can be designed so that the surface plasmon can be resonantly excited in the visible region to study SERS. In addition to obtaining surface plasmon resonance, we show that by combining more than a single resonance present in semiconductors, large enhancements in SERS can be attained. We demonstrate obtaining these large Raman signal enhancements in the SERS studies of 4-Mpy adsorbed on an etched ZnSe substrate and of N-719 dyes bound to TiO2 nanoclusters. We show enhancements of (2.5x106) in ZnSe and (4x1010) in TiO2 nanoclusters. This dissertation also focuses on the enhancement of phonon modes originating from an etched ZnSe nanostructure and CdSe QDs. In these investigations, we identify these phonon modes and corroborate our analysis with various experiments and theoretical models reported by previous investigators. We also assign symmetry of these phonon modes and propose selection rules to show that these vibrations are symmetry allowed. Moreover, we demonstrate that a combination of the charge-transfer and the exciton resonances are responsible for enhancing these phonon modes