Date of Graduation

12-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Microelectronics-Photonics (PhD)

Degree Level

Graduate

Department

Microelectronics-Photonics

Advisor/Mentor

Herzog, Joseph B.

Committee Member

Leftwich, Matthew B.

Second Committee Member

Muldoon, Timothy J.

Third Committee Member

Chen, Jingyi

Fourth Committee Member

Wise, Rick L.

Keywords

Nanofabrication; Nanosensor; Optical Enhancement; Optical Sensing; Plasmonics; SERS

Abstract

Technology based on the interaction between light and matter has entered something of a renaissance over the past few decades due to improved control over the creation of nanoscale patterns. Tunable nanofabrication has benefitted optical sensing, by which light is used to detect the presence or quantity of various substances. Through methods such as Raman spectroscopy, the optical spectra of solid, liquid, or gaseous samples act as fingerprints which help identify a single type of molecule amongst a background of potentially many other chemicals. This technique therefore offers great benefit to applications such as biomedical sensors, airport security, industrial waste management, water treatment, art/jewelry validation, and more. The primary setback of such techniques has been the difficulty of signal measurement, especially when the detected molecules are very sparse within a surrounding material, such as trace levels of a harmful chemical in a gas or liquid sample.

The ability to enhance light signals from such samples is key to developing affordable solutions to bring this type of optical sensing from being a research lab tool to an every-day technology. It has been found that local electric fields increase significantly by incorporating nanostructures onto surfaces containing the detected substances, thus increasing the signal strength measured at the detector. Using specially engineered metal nanostructures and their plasmonic resonance properties, signals such as Raman scattering from particles of interest can be enhanced to much more useable detection limits. This dissertation work employs two nanofabrication methods to engineer light enhancement to understand and improve real surface-enhanced Raman spectroscopy substrates that can predictably boost the identifying signals measured for probe molecules.

A lithography-based technique and a self-assembly process were studied for producing plasmonic nanostructures with at least one tunable geometrical parameter. These variable nanoscale features were the tuning knobs used during design engineering of optimal light enhancement through computational physics studies. Experimental enhanced Raman spectra were measured using plasmonic metasurfaces, with the signal enhancement found to corroborate theoretical calculations. The results demonstrated the effectiveness of the tunable devices as surface-enhanced sensing devices worthy of further development and study.

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