Plasmonics can achieve the tight optical confinement and localization in the subwavelength domain. Surface plasmon polaritons (SPPs) are closely related to coupling to emitters in excitation and emission, waveguiding, and active modulating on the nanoscale. Due to these phenomenon, plasmonic nanostructures can be used for applications, such as light emission, photodetection, optical sensing, and spectroscopy. Conventional plasmonic nanostructures can support plasmonic modes, and it is typically optimized for a single wavelength window with planar plasmonic structures.
Recent studies have reported some in-plane composite nanostructures and core-shell geometries can induce multiple plasmonic responses. However, it is challenging to achieve the control of individual plasmonic response due to the interdependent spectral tunability with changes in their in-plane geometries. In this dissertation, the concept of out-of-plane engineered nanoantenna structures is introduced, numerically calculated, and experimentally demonstrated. The nanolaminated MIM plasmonic structures show multiresonant plasmonic responses in the same antenna and each wavelength band can be tunable individually with different thicknesses of dielectric layers. The nanolaminated plasmonic structures has been reported for a scalable Surface-enhanced Raman spectroscopy (SERS) substrate for single-molecule sensitive and label-free chemical analysis. Due to the strong optical field confinement, the nanolaminated SERS substrates achieve increased SERS enhancement factor (EF) up to 1.6 x 108 with proper partial etching of dielectric layers. Furthermore, the nanolaminated MIM plasmonic structures have been successfully integrated with micro-scale pillar arrays to control the surface wettability for ultrasensitive SERS measurements. The hierarchical micro/nano plasmonic surface has densely packed intrinsic SERS-active hot spots that give rise to SERS EFs exceeding 107. This platform can take full advantage of low surface energy to control and measure the analyte in water droplets. Leidenfrost evaporation-assisted SERS sensing on the hierarchical substrates provides the way for ultrafast and ultrasensitive biochemical detections without a need for additional surface modifications and chemical treatments. / Doctor of Philosophy / The life in the 21th century has benefited from the technical revolutions of computational power that is based on the manipulation/storage of electrons. As predicted in Moore's law, the size of electronic microchip would go down, and the computational power has been enhanced due to the increase of transistor integration density. However, the two major factors, such as energy dissipation of electrons and signal delay of electronic circuit, limit the communication speed of electronics. These barriers have caused slowdown in the performance of computational power.
Photonic solutions have been offered to solve the limitations based on the larger bandwidth and a rare energy dissipation, compared to electronic counterparts. Moreover, optical communications typically demand much lighter channel to deliver similar power/information than practical electrical cables do. Thus, light manipulation/enhancement techniques are envisioned to overcome the limitations and guide to the methodology of interconnections between the electronic circuits and optical platforms.
Plasmonics can achieve the nanoscale light confinement and localization in the subwavelength domain. This strong confinement is originated from the coupling between the photons and the electron gas on the metal that results in surface plasmon polariton (SPP). SPPs are closely related to coupling to emitters in excitation and emission, waveguiding, and active modulating on the nanoscale. Due to these phenomenon, plasmonic nanostructures can be used for applications, such as light emission, photodetection, optical sensing, and spectroscopy.
In this dissertation, the concept of out-of-plane engineered nanoantenna structures is introduced, numerically calculated, and experimentally demonstrated. This vertically stacked nanoantenna structure is composed of metal-insulator-metal (MIM) laminates fabricated by physical vapor deposition techniques. Although conventional plasmonic nanostructures can support plasmonic modes, it is typically optimized for a single wavelength window. The nanolaminated MIM nanostructures, by contrast, can induce multiresonant plasmonic response in the same antenna with several advantages: (1) reduced individual footprint size and volume of nanoantenna, (2) accurate control of layer thicknesses by thin film deposition technique for resonance tuning, (3) easier integration with other functional materials as gap layers, and (4) efficient transport of charge carriers or heat in nanolaminated layers.
As a result of the tight optical field confinement, the nanolaminated plasmonic structures can be used for sensing application called Surface-enhanced Raman spectroscopy (SERS), which is a promising sensing platform for label-free biochemical analysis at the single-molecule level. Partial oxide etching process enables the analyte molecules to accommodate in strong enhancement region of the nanolaminated structures, resulting in amplified unique Raman features of molecular compounds as a finger print. The SERS enhancement factor is increased by one order of magnitude achieving 1.6x108. Furthermore, the nanolaminated plasmonic structures have been integrated with micro-scale pillar arrays to control the surface wettability for ultrasensitive SERS measurements.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/106808 |
| Date | 09 June 2020 |
| Creators | Song, Junyeob |
| Contributors | Electrical Engineering, Zhou, Wei, Vikesland, Peter J., Agrawal, Amit, Jia, Xiaoting, Ha, Dong S., Lester, Luke F. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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