Developing Parallel 3D FDTD Numerical Models for Studying Plasmonic Nanostructures and Their Applications
| Autor: | Hui-Hsin Hsiao, 蕭惠心 |
|---|---|
| Rok vydání: | 2013 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 In this dissertation, a parallelized three dimensional (3D) finite-difference time-domain (FDTD) numerical simulator is developed and applied to the study of the following three main topics. First, we start with the discussion for a basic metallic-grating/dielectric/metal (MDM) metamaterial absorber structure. The localized surface plasmon (LSP) resonances within this structure in fact are associated with the x-directional Fabry-P´erot like resonances, and the induced surface currents within the metallic strip and metallic film accompanied with the displacement currents within the dielectric layer form a current loop for the LSP mode, thus resulting a non-zero magnetic moment. Besides, we further investigate a more complex structure with two inversely-stacked MDMs, and the current loops between the top and bottom resonators construct two opposite-signed magnetic moments with the intense one residing in the thinner dielectric layer. The 2nd LSP mode is measured by the experiment under the incident angle θ = 12◦, while it is absent in the simulated spectra as a result of no net dipole for even order LSP modes under normal incidence. The second topic is related to extraordinary transmission (EOT) phenomenon. We first examine the transmission spectra and near-field distributions of periodic U- to H-shaped apertures and find some unique near-field profiles for surface electromagnetic modes and Wood’s anomalies are consistent with the theoretical studies. Then, we focus on the near-field characteristics for shape resonances combined with the symmetric requirement to predict the shape resonant paths for more complex-shaped apertures. The predictions agree well with the real resonant modes calculated by the FDTD method. By applying the modified approximation equation for the cutoff wavelengths of the rectangular waveguide, we can further estimate the resonant wavelengths with the error below 11 % compared with FDTD results. Besides, the spectral effect of the separation distances between apertures within one unit cell is analyzed, which demonstrates the coupling between adjacent slits would play a role in the variation of the spectra. Finally, we study the physical origin for the high-contrast microscopic image of a transparent silver nanoparticles/anodic aluminum oxide (Ag-NPs/AAO) SERS substrate. By analyzing the backward-scattering radar cross section (RCS) for the substrate and for the system with a bacteria residing above the substrate, we find the difference of the RCS will be more obvious within the range of the plasmonic resonance. In addition, from the near-field features, the hot spots become a little bit dimmer (bighter) for |E| (|H|) distributions within the area covered by the bacterium for the LSP resonance, while those differences become indistinct for the off-resonant situation. Moreover, we also investigate the optical properties of a hybrid nanoshell-nanosphere SERS substrate. From the near-field analyses, we find the electric fields are strongly localized near the contact points between the nanoshells and gold nanospheres compared with those sites between nanoshells, while the |H| distributions are quite uniform among the surfaces, and thus would be more probable to contribute to the far-field scattered power. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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