title: Fast Assembly of Gold Nanoparticles in Large-Area 2D Nanogrids Using a One-Step, Near-Infrared Radiation-Assisted Evaporation Process.
abstract: When fabricating photonic crystals from suspensions in volatile liquids using the horizontal deposition method, the conventional approach is to evaporate slowly to increase the time for particles to settle in an ordered, periodic close-packed structure. Here, we show that the greatest ordering of 10 nm aqueous gold nanoparticles (AuNPs) in a template of larger spherical polymer particles (mean diameter of 338 nm) is achieved with very fast water evaporation rates obtained with near-infrared radiative heating. Fabrication of arrays over areas of a few cm(2) takes only 7 min. The assembly process requires that the evaporation rate is fast relative to the particles' Brownian diffusion. Then a two-dimensional colloidal crystal forms at the falling surface, which acts as a sieve through which the AuNPs pass, according to our Langevin dynamics computer simulations. With sufficiently fast evaporation rates, we create a hybrid structure consisting of a two-dimensional AuNP nanoarray (or "nanogrid") on top of a three-dimensional polymer opal. The process is simple, fast, and one-step. The interplay between the optical response of the plasmonic Au nanoarray and the microstructuring of the photonic opal results in unusual optical spectra with two extinction peaks, which are analyzed via finite-difference time-domain method simulations. Comparison between experimental and modeling results reveals a strong interplay of plasmonic modes and collective photonic effects, including the formation of a high-order stopband and slow-light-enhanced plasmonic absorption. The structures, and hence their optical signatures, are tuned by adjusting the evaporation rate via the infrared power density.
authors.forename: André
authors.initials: A
authors.lastname: Utgenannt
authors.forename: Ross
authors.initials: R
authors.lastname: Maspero
authors.forename: Andrea
authors.initials: A
authors.lastname: Fortini
authors.forename: Rebecca
authors.initials: R
authors.lastname: Turner
authors.forename: Marian
authors.initials: M
authors.lastname: Florescu
authors.forename: Christopher
authors.initials: C
authors.lastname: Jeynes
authors.affiliation: Physics and Astronomy, Faculty of Physical Sciences and Engineering, University of Southampton , Highfield, Southampton, SO17 1BJ, U.K.
authors.forename: Antonios G
authors.initials: AG
authors.lastname: Kanaras
authors.affiliation: Physics and Astronomy, Faculty of Physical Sciences and Engineering, University of Southampton , Highfield, Southampton, SO17 1BJ, U.K.
authors.forename: Otto L
authors.initials: OL
authors.lastname: Muskens
authors.forename: Richard P
authors.initials: RP
authors.lastname: Sear
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Keddie
keywords: IR heating; coupling; evaporation; gold nanoparticles; inverse opal; photonics; plasmonics; self-assembly