M.Sc Thesis

M.Sc StudentYakir Ishay
SubjectAnalyzing Localized Plasmon Resonance in Complex Three
Dimensional Geometries Using Source Model
DepartmentDepartment of Electrical Engineering
Supervisor Professor Bartal Guy
Full Thesis textFull thesis text - English Version


Studying the interaction of light with nanosized structures is important both theoretically and from technological point of view. In particular, plasmonic nanostructures show an interesting behavior where an electromagnetic field can excite collective oscillations of free electrons giving rise to complex resonant behavior with strong near-field enhancement and localization. The localized plasmon resonance is governed by the dielectric function of the metallic objects and by their geometry. While spherical (or close to spherical) nanoparticles (NPs) exhibit resonance frequencies in the visible spectrum, 3D non-spherical (NS) NPs might reveal Near Infrared resonance frequency and other interesting behaviors such as broad-band field enhancement.

However, simulating 3D NP is a challenging task, specifically sub-wavelength NPs possess areas with relatively small radii of curvatures and large field gradients. The shortcoming of the commonly used simulation tools, based on finite difference time domain (FDTD) or finite element method (FEM), in calculating the electromagnetic fields in such system is well known; they often fail to simulate the fields around complicated NPs with no defined symmetry, as it requires enormous calculation time and resources, especially for "exotic" NPs that either lack any symmetry or involving areas with very small radii of curvatures (or both).

In order to properly investigate such "exotic" particles, we have developed a new algorithm based on the Source-Model Technique (SMT) for fast, accurate and robust calculation of the Electro-Magnetic fields, irrespective of how complicated the NP is or what it is combined of. In particular, we have tailored this new surface curvature base source distribution (SCBSD) algorithm to handle such NS-NPs. The thesis deals with theoretical investigation of localized plasmon resonance in 3D NS geometries.

In the first part of our research we specify SCBSD algorithm and test it for several canonical problems such as scattering by a plasmonic sphere and ellipsoid.

In the second part we focus on scattering from NS metallic NPs: high aspect ratio ellipsoid, Asymmetric dimer of spheres, peanut-shell and cashew nut surfaces. In latter cases we show two new features associated with the unique shape of the nanoparticles. Lastly, we compare our method to Boundary Element Method (BEM) in terms of speed and accuracy of results.