EXPLORING NANOSTRUCTURES FOR APPLICATIONS IN HUMIDITY SENSING AND ACTIVE PLASMONICS
Open Access
Author:
Walker, Thomas R.
Graduate Program:
Engineering Science
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 14, 2008
Committee Members:
Jun Huang, Thesis Advisor/Co-Advisor Jun Huang, Thesis Advisor/Co-Advisor
Keywords:
NEMS humidity sensing active plasmonics MEMS
Abstract:
An optical humidity sensor based on a nanoporous, polymeric photonic crystal (PC) is demonstrated. The PC sensing structure is created by combining a holographic interference patterning technique with a modified holographic, polymer-dispersed liquid crystal system. Changes in relative humidity (RH) induce the modification of the refractive index contrast between the nanoporous and nonporous regions — and thus between the transmittance and bandgap position — of the PC structure. For a PC structure with 30% porosity and a grating spacing of 220 nm, a change in the RH from 40% to 95% at 34°C results in a redshift of 43 nm in the central wavelength at the PC bandgap and an increase from 12% to 87% in the relative transmittance at ? = 600 nm. Other performance analyses have shown that the nanoporous, polymeric PC-based humidity sensor is highly stable and reproducible, exhibits minimal hysteresis, and responds relatively quickly.
Further, we have fabricated close-packed arrays of gold-coated polystyrene nanospheres upon PDMS substrates. By stretching and squeezing the PDMS, we controllably, reversibly changed the plasmonic properties of the arrays. We also simulated by a finite-difference time-domain method how rearranging such arrays affects their plasmonic properties.
