AUTHOR=Han Donghoon , Crouch Garrison M. , Chao Zhongmou , Fullerton-Shirey Susan K. , Go David B. , Bohn Paul W. 

TITLE=Nanopore-Templated Silver Nanoparticle Arrays Photopolymerized in Zero-Mode Waveguides

JOURNAL=Frontiers in Chemistry

VOLUME=Volume 7 - 2019

YEAR=2019

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2019.00216

DOI=10.3389/fchem.2019.00216

ISSN=2296-2646

ABSTRACT=In situ fabrication of nanostructures within a solid-polymer electrolyte confined to subwavelength-diameter nanoapertures is a promising approach for producing nanomaterials for nanophotonic and chemical sensing applications.  The solid-polymer electrolyte can be patterned by lithographic photopolymerization of poly(ethylene glycol) diacrylate (PEGDA)-based silver cation (Ag+)-containing polyelectrolyte.  Here, we present a new method for fabricating nanopore-templated Ag nanoparticle (AgNP) arrays by in situ photopolymerization using a zero-mode waveguide (ZMW) array to simultaneously template embedded AgNPs and control the spatial distribution of the optical field used for photopolymerization.  The approach starts with an array of nanopore-confined recessed Ag ring electrodes fabricated by sequential layer-by-layer deposition and focused ion beam milling.  These structures have an optically transparent bottom, allowing access of the optical radiation to the attoliter-volume ZMW region to photopolymerize a PEGDA monomer solution containing AgNPs and Ag+.  The electric field intensity distribution is calculated for various ZMW optical cladding layer thicknesses using finite-element simulations, closely following the light-blocking efficiency of the optical cladding layer.  The fidelity of the polyelectrolyte nanopillar pattern was optimized with respect to experimental conditions, including the presence or absence of Ag+ and AgNPs and the concentrations of PEGDA and Ag+.  The self-templated approach for photopatterning high-resolution photolabile polyelectrolyte nanostructures directly within a ZMW array could lead to a new class of metamaterials formed by embedding metal nanoparticles within a dielectric in a well-defined spatial array.