PhD Thesis Defense: Timothy J. Palinski

Thursday, July 18, 2019, 2:00–4:00pm

Rm 201 (Rett's Rm), MacLean ESC

“Plasmonic metasurfaces as molecular sensors: theory, nanofabrication, and on-chip applications”

Abstract

In this thesis, we present the theory, design, and nanofabrication of plasmonic metasurfaces, which form the foundation of an emerging class of sensitive, compact, and field-deployable biosensors. Localized surface plasmons present in metallic nanostructures are the underlying cause of many unique optical properties, including the bright structural coloration of stained- glass windows, subwavelength focusing of light, optical invisibility cloaking, and single- molecule biosensing. These coupled electron-electromagnetic surface waves may be used to shape both the amplitude and phase of electromagnetic fields at subwavelength scales. The nanofabrication techniques presented here enable novel devices for the extreme focusing of light into subwavelength hot-spots, leading to ultrasensitive biosensing capabilities, as well as subwavelength waveguiding for integrated on-chip applications.

A major challenge of optical/plasmonic sensing is the effective far-field detection of near-field sensing information (e.g., molecular binding events). Traditional detection approaches rely on cumbersome, laboratory-based equipment to interrogate the sensor. Integrated optical waveguides have been studied as a means towards device miniaturization, however they often lack the desired sensitivity. By harnessing the unique optical properties of metallic nanostructures, we seek to bridge the sensitivity gap, while maintaining a compact, lab-on-chip platform. Towards this end, we studied two classes of plasmonic metasurface-based sensors for on-chip application: (i) a metallic photonic crystal (MPC)-based sensor, consisting of a plasmonic grating coupled to a photonic waveguide, and (ii) a large-area metal-insulator-metal (MIM) sensor with an active polymer spacer. The MPC sensor was tested over a wide temperature range (180 K to 300 K) and exhibited high stability, varying by less than 5% in reflected signal. Further, wider gratings were found to enhance the plasmonic-photonic coupling and device sensitivity, with calculated Rabi splitting up to 450 meV. The macroscopic extent of the MIM sensor enabled naked-eye detection of volatile organic compounds via analyte-induced swelling of the polymer spacer. A change in spacer thickness of just 10 nm produced a dramatic shift in color, as evidenced by a nearly 50 nm shift in resonance. Furthermore, the response was shown to be fast and fully reversible. These promising results may help open the door to new lab-on-chip capabilities, including in extreme environments.

Thesis Committee

For more information, contact Daryl Laware at daryl.a.laware@dartmouth.edu.