Date

2023-1-26

Author

Yüksel, Selen

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Surface Enhanced Raman Scattering (SERS) is a surface-sensitive vibrational spectroscopy technique. Highly SERS-active substrates made of nanostructured noble metals have been widely investigated owing their activity to the formation of localized surface plasmon resonances, hotspots, where electromagnetic field is amplified by several orders of magnitude locally. Silver and gold are the two most studied noble metals due to their especially low losses and hence high enhancement factors (EF). Gold is chemically stable which is ideal against aging however silver possesses lower losses. Therefore, despite their high EF, silver nanostructures are useful only with a suitable protective coating layer. As an analytic tool, use of SERS has been proven in detection of trace molecules countless times. However, its use has been limited in the detection of larger scale materials including biological pathogens. Recently thick and dense AgNW networks in the form of filter foils have been developed for this aim with the dual function of filtering the pathogens from liquids and also acting as a SERS substrate. In this thesis work, it is aimed to estimate the expected Raman EF of AgNWs using numerical simulations. Finite-difference time-domain (FDTD) based Maxwell solver is used for its versatility, availability and well-established literature in this work. In our approach EF of complex AgNW networks is estimated using FDTD method by dividing them into sub-systems represented by two mutually parallel- and cross-oriented AgNWs. Simulations are conducted to assess the dependence of EF to distance between parallel and crossed wires, and to protective dielectric coating thickness, and the polarization angle. Calculated estimates of EF values are found to range from 1E+04 to 1E+07 which agree very well with the experimental studies carried out in our research group. This is a surprising result considering the simplicity of our approach against the complexity of the actual AgNW network.

Subject Keywords

Surface Enhanced Raman Scattering, Enhancement Factor, Silver, Nanowire, Filter

URI

https://hdl.handle.net/11511/101992

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Graduate School of Natural and Applied Sciences, Thesis