Ahmad Mohammadi

In this thesis, we design and model plasmonic nanocavities with different geometries by utilizing optical phenomena including Fabry-Perot, localized surface plasmon, and scattering. For this purpose, we consider aperture nanocavities with geometries including cylinder and cone embedded in a metal layer made of gold and silver with a silica substrate. Investigating the influence of effective parameters such as dimensions, geometry, refractive index of the surrounding environment, and the material of plasmonic nanocavities, as well as studying the interaction of light with such structures, is not analytically possible and computational techniques must be used. For this purpose, we use the Finite-Difference Time-Domain method due to its ability to solve Maxwell's equations in the time domain for complex structures with arbitrary dimensions and shapes. We demonstrate that with precise design of the dimensions, geometry, and material of plasmonic nanocavities, electromagnetic field enhancement can be achieved in very small regions. With slight manipulation of the refractive index of the surrounding environment, the resonance peak of localized surface plasmon and Fabry-Perot shifts well, resulting in significantly increased sensitivity of the structure. We calculate the sensitivity, quality factor, and figure of merit parameters for the designed nanocavities and show that by precisely adjusting all effective parameters, a nanosensor based on the presented nanocavities can be proposed that has high sensitivity