Sponsor
Portland State University. Department of Physics
First Advisor
Rolf Könenkamp
Term of Graduation
Summer 2025
Date of Publication
8-19-2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy (Ph.D.) in Applied Physics
Department
Physics
Language
English
Subjects
COMSOL simulation, Fano resonance, Photoemission Electron Microscopy, Plasmonics, Refractive index sensing, Silver nanotriangles
Physical Description
1 online resource (xv, 126 pages)
Abstract
This thesis presents a detailed investigation of plasmonic sensors based on silver (Ag) nanotriangles, focusing on the interaction of plasmonic mode with waveguide modes to achieve Fano resonance for enhanced refractive index sensitivity. For this purpose, Ag nanotriangles were chemically synthesized and were on indium tin oxide (ITO)-coated glass. The samples were illuminated with laser light of various wavelengths and polarization to excite surface plasmon in the nanotriangle. Observation and characterization of their plasmonic behavior was done experimentally using Photoemission Electron Microscopy (PEEM). Numerical simulations using the Finite Element Method (FEM) were performed that agreed with these experimental results and provided further insight into the plasmonic behavior. Fano resonance condition was studied exclusively through FEM simulations, allowing precise control over geometry, wavelength, and angle of incidence. The simulation revealed that Fano resonance was achieved by coupling surface plasmons in single Ag nanotriangles (excited by edge coupling) to a waveguide mode in the ITO layer through a spacer layer, resulting in asymmetric spectral features. The study was extended to include both 2D and 3D models. In 2D geometries with planar semi-infinite Ag layers, Fano resonances exhibited sharper spectral features, while in 3D nanotriangle configurations, the characteristic asymmetry and spectral narrowing persisted, but spectral features broadened with decreasing size. Additionally, a triangular cavity in Ag layers was investigated based on Babinet's principle, showing stronger plasmonic field enhancement compared to solid nanotriangles. The sensitivity of the Fano resonance of these structures were determined and were compared with the sensitivity of the plasmon resonance by altering the refractive index of the surrounding medium simulating the presence of analytes. In each case the Fano resonance showed higher sensitivity in comparison to plasmon resonance sensitivity in each type of structure. Furthermore, it was seen that Fano resonance showed stronger sensitivity in the Ag cavity in comparison to the Ag solid nanotriangle.
Rights
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Persistent Identifier
https://archives.pdx.edu/ds/psu/44111
Recommended Citation
Islam, Nabila, "Evaluation of Fano Resonance in Silver Nanotriangles and Complementary Triangular Apertures for Enhanced Refractive Index Sensing" (2025). Dissertations and Theses. Paper 6927.