The formation and enhancement of heterostructures to optimize surface plasmon propagation in nano-optics devices

This thesis focuses on the formation of heterogeneous structures, and their optimization to form improved components for nanocircuits; including light source, antenna incorporation for enhanced wave guiding, and probe tip fabrication for device testing. A method was developed for the heteroaggregation assisted wet synthesis of core-shell nanowires by coating silver nanowires with a thin silica layer followed by an outer shell of CdSe or Au nanoparticles. Total coverage of nanoparticles on nanowires was found to increase with the nanoparticle size, which is attributed to the increase in the van der Waals interaction between the nanoparticles and the nanowire with the increasing size of nanoparticles, with steric repulsion also contributing due length of capping ligands limiting the overall achievable coverage. Investigation of the core-shell nanowire’s optical properties yielded CdSe Raman peak enhancement by a factor of 2-3 due to the excitation of surface plasmon propagation making them suitable for probe tip incorporation. A CdSe-SiO2-Si heterostructure was developed and optimized by determining the optimum silica layer thickness for different CdSe block thicknesses through COMSOL simulations to form a nanocircuit light source. Once obtained; the optimum structure was formed through electrophoretic deposition of CdSe on silica coated silicon wafers and tested for lasing. A 500 nm thick CdSe layer on 100 nm of silica coated silver nanowires showed a lasing peak around 670 nm highlighting the effective mode confinement. The optimum thickness for trench patterns was also determined through simulations; though no further enhancement was achievable through antenna use. The overall improvement in surface plasmon waveguide propagation afforded by antenna structures was investigated by comparing bowtie and semicircle antenna for the surface plasmon propagation in Au-Mica trench patterned and line cut plain waveguide structures both experimentally and through COMSOL simulations. Both the effects of polarization and wavelength were investigated and discussed. In a broadband system; the bowtie antenna was shown to result in an enhancement factor of 2.12 ± 0.40 when the beam was perpendicular to the regular waveguide yet with no enhancement for parallel polarizations, and for the line cut strong enhancement for a parallel polarization with no noticeable enhancement for the perpendicular condition. Similar results were obtained for the semicircle antenna for the line cut; yet with no noticeable enhancement for the trench cut plain waveguide structure. This was found to be due to the excitation of different modes: surface plasmon modes and gap modes, depending on beam polarization. The mode leakage into the substrate was also discussed. The effects of filling the trench and line cut structures with semiconductor materials for the Au-Mica substrates are also investigated through COMSOL simulations. Filling the Au-Mica line cuts improves surface plasmon propagation by a factor of 10 due to improved mode confinement. The potential for a multi-slit design was also discussed as well as the change in mode leakage.