FABRICATION AND CHARACTERIZATION OF SERS SUBSTRATES VIA LASER INDUCED PHOTOCHEMICAL SURFACE ROUGHENING OF SILICON

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2022-6-10

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Akbıyık, Alp

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In this thesis, Surface-Enhanced Raman Spectroscopy (SERS) substrates are fabricated using laser assisted chemical etching of silicon as a surface nanostructuring technique. As a novel method of control over the structuring parameters, the incident laser illumination is spatially modified via a Digital Micromirror Device (DMD) that enable fast and uniform fabrication of complex structures. Onto the photochemically nanostructured silicon surfaces, silver and gold films are deposited by thermal evaporation or nanoparticles are formed to transform the roughened Si surfaces into the SERS substrates. The thickness of Ag and Au on the structured Si is shown to significantly alter the SERS spectra. The increase of the SERS signal is also attributed to the electromagnetic field enhancement that result from the surface roughness of Si which is controlled by the illumination power, duration and the spot size of the laser beam. For the characterization of the SERS substrates, Raman spectra of the dye molecule Brilliant Cresyl Blue (BCB) can be observed down to nM orders. Fabricated substrates are also compared under 660 nm and 532 nm excitations. Nanostructured Si surface with Ag deposition is shown to create more enhancement than Au deposition under 532 nm excitation with an enhancement factor (EF) up to 10^9. EF is calculated and SERS performance is evaluated based on both SERS and dark-field scattering spectra experimentally, and using Finite-Difference Time-Domain (FDTD) simulations, numerically. Further range of applicability of the substrates are investigated by testing with the molecules Crystal Violet (CV), Rhodamine 6G and ammonium nitrate from which large enhancements are obtained.

Subject Keywords

Laser-assisted chemical etching, surface roughening of silicon, Surface- Enhanced Raman Spectroscopy, SERS substrate

URI

https://hdl.handle.net/11511/97861

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

A. Akbıyık, “FABRICATION AND CHARACTERIZATION OF SERS SUBSTRATES VIA LASER INDUCED PHOTOCHEMICAL SURFACE ROUGHENING OF SILICON,” M.S. - Master of Science, Middle East Technical University, 2022.