Surface Enhanced Raman Spectroscopy of the plasmonic nanogratings obtained by Laser Induced Periodic Surface Structuring

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MSc-Thesis-Serena Nur Erkızan.pdf

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2023-1-31

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Erkızan, Serena Nur

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The research conducted in this study presents a novel method of generating highly sensitive Surface Enhanced Raman Spectroscopy (SERS) substrates by femtosecond laser writing techniques. Two different types of periodicity regimes are introduced by femtosecond laser-based nano-structuring of crystalline Silicon (Si) and generated patterns are classified as Low Spatial Frequency LIPSS (LSFL) and High Spatial Frequency LIPSS (HSFL). Quasi periodic, self-organized femtosecond laser written periodic nanostructures can embody required plasmonic gap distance, roughness and randomness to accommodate high hotspot density and enhancement factor of SERS. Silver (Ag) deposited nanoripples with different periodicity regimes exhibit state of art SERS enhancement factor as high as 10^9 with 10^-11 M limit of detection for Crystal Violet (CV) molecule. Enhancement factor dependence of the SERS substrates is investigated at Raman excitation wavelength 532, 660 and 785 nm. Raman enhancement factor simulations for all excitation wavelengths are performed by Finite Elements Method (FEM) based Maxwell solver by using COMSOL Multiphysics. Enhancement factor results obtained by measured SERS spectra and electric field enhancement simulations exhibit good agreement between them. A major advantage introduced by femtosecond laser-based SERS substrates is accurate and flexible control of processed region without restricting processing over large areas compared to well established top-down approaches such as nanoimprint lithography, electron beam lithography, chemical plasma etching. Fs-nanoripple generation do not require multiple processing steps like in nanoimprint lithography including stamp production of nanostructures, pattern transfer and peeling off. On the contrary of chemically synthesized and aggregated nanoparticle colloids, metal deposited quasi-periodic nanoripples offer reproducibility of obtained SERS signal over large areas and chemical stability for SERS aging measurements.

Subject Keywords

Surface Enhanced Raman Scattering, Femtosecond Laser Induced Periodic Surface Structuring

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https://hdl.handle.net/11511/102552

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

S. N. Erkızan, “Surface Enhanced Raman Spectroscopy of the plasmonic nanogratings obtained by Laser Induced Periodic Surface Structuring,” M.S. - Master of Science, Middle East Technical University, 2023.