M.Sc Student | Ishay Yakir |
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Subject | Analyzing Localized Plasmon Resonance in Complex Three Dimensional Geometries Using Source Model Technique |

Department | Department of Electrical Engineering |

Supervisor | Professor Guy Bartal |

Full Thesis text |

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.