Exploring phenomena occurring at the molecular level is critical to deepen our understanding of the living world. However conventional analytical tools are often limited in both spatial resolution and sensitivity. In this work we evaluate how fractal plasmonic structures can be developed for Surface Enhanced InfraRed Absorption (SEIRA) substrates to boost the infrared fingerprint signal of unknown single entities such as nanomaterials, virus or other biological systems. In this thesis, we present an overview of developments using light-matter interaction to push the limit of spatial resolution and sensitivity (Chapter 1). We discuss technological advances that allow nanoscale infrared spectroscopy despite inherent diffraction limit and remaining limitations in the field. In Chapter 2, we delve into the principles of techniques used in our work and compare them with other state-of-the-art in the field. We expand on the principle of nanoscale infrared spectroscopy and introduce how existing capabilities are uniquely suited to explore the near-field behavior of plasmonic structures at the nanoscale. In Chapter 3, we describe the design and fabrication of fractal Cesaro geometries we selected to evaluate broadband signal enhancement. The approaches used for far-field and near-field characterization of the plasmonic behavior are presented. In Chapter 4, we present our experimental results describing the behavior of Cesaro fractals with increasing levels of complexity. After confirming the far-field infrared resonances in the mid-infrared range in higher order structures, we coat the structures with a thin polymer film to map the regions with the highest photothermal enhancements, as an indirect indication of the near-field behavior of the plasmonic structures. We show that different film thicknesses of the polymer deposited on the plasmonic substrates provide some insight on the effect of photothermal propagation, which influences the signal level and spatial resolution of nanoscale infrared (nanoIR) spectroscopy and microscopy measurements. Signal enhancement performance of our structures is evaluated as a function of excitation frequency, laser power, laser pulse width, and sample orientation. Finally, we provide a summary of our work in Chapter 5. We also discuss types of samples for which our structures might be beneficial and consider outlooks on future work of this project.
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Master of Science (M.S.)
College of Graduate Studies
Nanoscience Technology Center
Length of Campus-only Access
Masters Thesis (Open Access)
Rutins, Guntis, "Signal Enhancement Techniques for Nanoscale Infrared Spectroscopy Using Fractal Plasmonic Structures" (2022). Electronic Theses and Dissertations, 2020-. 1647.