Effects of Corner Radius on Periodic Nanoantenna and Anti-reflection Textured Structures for Surface-enhanced Raman Spectroscopy
Date Issued
2016
Date
2016
Author(s)
Chao, Bo-Kai
Abstract
Two main research topics were shown in the present study. In the first topic, the corner radius effects in periodic nanoantenna for surface-enhanced Raman spectroscopy (SERS) were discussed. Corner radius is a concept to approximate the fabrication limitation due to the effective beam broadening at the corner. The purpose of the present study is to investigate the effects of corner radius on the electromagnetic field enhancement and resonance wavelength for three periodic polygon dimers of bowtie, twin square, and twin pentagon. The enhancement factor of surface-enhanced Raman spectroscopy due to the localized surface plasmon resonances in fabricated gold bowtie nanostructures was investigated using both Raman spectroscopy and finite-difference time-domain (FDTD) simulations. The simulated enhancement factor versus corner radius relation was in agreement with measurements and it could be fitted by a power-law relation. In addition, the resonance wavelength showed blue shift with the increasing corner radius because of the increasing dispersion of concentrated charges in a larger area. For different polygons, the corner radius instead of the tip angle is the dominant factor of the electromagnetic field enhancement because the surface charges tend to localize at the corner. Also, the fractional resonance wavelength shift versus the product of gap size and corner radius relation could be fitted by a power-law relation for each periodic polygon dimer nanostructure. In the second part, a high surface area and low reflection textured surface-enhanced Raman scattering substrate with plasmonic gold nanodroplets fabricated by wet etching and island lithography was reported. The optical properties obtained from the finite-difference time-domain simulation results showed the agreement with reflection and dark-field scattering measurements. According to the AFM and reflection measurements, the nanopillar-on-pyramid structure provided large surface area and multiple reflections for SERS enhancements. The SERS enhancement of nanopillar-on-pyramid SERS substrate was about 2 orders of magnitude larger than the gold film substrate. Although the SERS signals varied in the different measured regions, the SERS substrates with nanopillar-on-pyramid structure always have the stronger enhancement factor than the other SERS substrates.
Subjects
Corner radius
Plasmonics
Finite-difference time-domain method
Surface-enhanced Raman scattering
CsCl nanoisland
Anti-reflection
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-105-D98527007-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
(MD5):4d57dbe38902e6bc47390ba2909d14a2