Fabrication of Polymeric and Plasmonic Patterns on Flexible Substrate Based on Nanoimprint Lithography and Its Application to Superhydrophobic Surface and Refractive-Index Sensor

Abstract

In recent years an increasing number of nontraditional applications have been developed in the areas of photonics applications organic electronics and biotechnology In particular flexible device applications which include electronic devices light-emitting devices solar cells energy storage devices optical devices flexible displays artificial iris surface-enhanced Raman scattering nanopaper transducers biomedical devices bioinspired materials and sensors have gained considerable interest from various fields Compared with conventional lithography such as photolithography and e-beam lithography nanoimprint lithography (NIL) is a suitable method to imprint the resist directly on flexible substrates because it can mold the resist on a nonflat surface However flexible substrates cannot be integrated easily into conventional integrated circuit fabrication processes because of the incompatibility of photoresists low thermal stability and complex fabrication procedures Multiple processes should be eliminated and dry etching or solvent treatment should be avoided Several researchers have introduced many approaches based on NIL In this thesis we demonstrate three straightforward and convenient processes which can fabricate polymeric patterns or metallic nanostructure on a flexible substrate In the first section we show a reliable process for the direct nanoimprinting of a flexible polycarbonate (PC) sheet using a perfluoropolyether (PFPE) mold The imprint performance of PFPE hard/soft- PDMS and silicon molds are compared Only PFPE mold can be fully patterned into PC substrate with viable integrity at a low heating temperature and applying pressure The mechanical property and gas permeability of the materials are investigated Finally nanoroughness-on-nanopillar hierarchical surfaces which possess superhydrophobic slippery characteristics are obtained by treating PC nanopillar arrays imprinted by PFPE mold with C4F8 plasma In the second section we demonstrated the plasmonic metallic nanostructure fabricated by direct nanoimprinting of gold nanoparticles (AuNPs) The localized surface plasmon resonance properties of AuNPs or gold pillar arrays can be controlled and tuned during the annealing process We apply this gold pillar arrays to refractive index sensing The corresponding resonance wavelengths can be widely tuned from the visible to infrared region by changing the size of the gold pillars thus providing a broad range of sensing capability In the third section we present a novel process based on nanotransfer printing for fabricating gold nano-pleat arrays The gold film deposited over nano-ridge arrays on a PFPE mold was transferred directly to an NOA63 film on a glass substrate The width of the nanocavities on the nano-pleat array can be dramatically reduced compared with the width of the nanoridges on the mold The mechanisms of remarkable reduction in the nanocavity width during the gold sputtering process were investigated Plasmonic properties of nano-pleat arrays have been studied numerically and experimentally A sharp phase dip was used for refractive index sensing demonstrating an excellent sensitivity with a figure of merit of 40 1 Above proposed fabrication processes are very simple low-cost and high throughput Thus these are promising candidates for flexible device fabrication

Date of Award	2016 May 26
Original language	English
Supervisor	Chun-Hung Lin (Supervisor)