Fabrication and characterization of three-dimensional copper metallodielectric photonic crystals

Abstract

Three-dimensional metallodielectric photonic crystals were created by fabricating a micron-scale polymeric template using multiphoton direct laser writing (DLW) in SU-8 and conformally and selectively coating the template with copper (Cu) via nanoparticle-nucleated electroless metallization. This process deposits a uniform metal coating, even deep within a lattice, because it is not directional like sputter-coating or evaporative deposition. Infrared reflectance spectra show that upon metallization the optical behavior transitions fully from a dielectric photonic crystal to that of a metal photonic crystal (MPC). After depositing 50 nm of Cu, the MPCs exhibit a strong plasmonic stop band having reflectance greater than 80% across the measured part of the band and reaching as high as 95% at some wavelengths. Numerical simulations match remarkably well with the experimental data and predict all dominant features observed in the reflectance measurements, showing that the MPCs are structurally well formed. These data show that the Cu-based process can be used to create high performance MPCs and devices that are difficult or impossible to fabricate by other means.

Low‐Distortion Surface Functionalization of Polymeric Microstructures

“…To assess the efficacy of the aqueous amination method, we examined how well it serves to prime surfaces for electroless deposition of copper. In the copper deposition process (Figure ), a polymeric surface is first aminated then treated with aqueous HAuCl 3 to bind Au(III) to the pendant amines. The Au(III)‐treated surface is then exposed to NaBH 4 , which reduces the gold cations, forming gold nanoparticles in situ .…”

“…Immediately following amination, the sample was rinsed with water and immersed in a 0.53 × 10 −3 m aqueous solution of HAuCl 4 for 2 h. The sample was then removed from the gold bath, rinsed with water, and immersed in 0.1 m aqueous NaBH 4 for 2 min to generate gold nanoparticles by in situ reduction on the polymer matrix . The samples were then removed from the reduction bath, rinsed in water, and immersed in a copper plating bath for 7 min . The copper plating bath was prepared by dissolving 0.75 g of copper sulfate, 1 g of sodium hydroxide, and 3.5 g of sodium potassium tartrate in 25 mL of water.…”

“…Several investigators have shown that metal can be selectively coated onto 3D microstructures by electroless metallization . Electroless metallization is achieved by i) functionalizing a polymer surface with binding groups, such as EDA; ii) binding a metallization sensitizer or catalyst, such as metal nanoparticles; then iii) immersing the sample into a metastable solution that deposits the target metal conformally onto the sensitized surface.…”

“…One simple and widely used method for aminating a polymeric surface or microstructure involves immersing it into a solution of an aminating agent dissolved in an organic solvent, such as EDA‐in‐ethanol . Although it is well established that treatment with ethanolic EDA and related methods are effective for aminating surfaces, little attention has been devoted to how these processes affect the form and integrity of a microstructure.…”

Simple Implementation of Arbitrarily Shaped Total-Field/Scattered-Field Regions in Finite-Difference Frequency-Domain

“…In these cases, iterative algorithms [19,20] or alternate techniques like the slice absorption method [21,22] are recommended.…”