Ultra-smooth and ultra-large single crystalline gold flakes for large-area plasmonics
You-Xing Huang1*, kel meng see1, Jer-Shing Huang1
1Department of chemistry, National Tsing Hua University, Hsinchu, Taiwan
* presenting author:黃右昕, email:anson820302@gmail.com
Plasmonic nanostructure has been widely used to enhance nanoscale light-matter interaction. Single-crystalline thin gold flakes have no grain boundaries and surface roughness and the scattering loss of surface plasmon polaritons is minimized. Therefore, they can serve as ultrasmooth substrate for the fabrication of high-definition plasmonic nanostructures. Synthesizing large and thin flakes is not easy because large flakes usually contain defects and their thickness is typically proportional to the size. Therefore, the synthesis of flat gold plates with large area and thin thickness, i.e. large aspect ratio, is of great interest but still remains a challenge. Here, we demonstrate a new simple method for synthesizing single crystalline sub-millimeter gold flakes. We synthesize the gold flakes by heating the mixture of ethylene glycol and HAuCl4 without adding any other additional reducing agent. With optimized experimental conditions, the size of gold flakes can reach 740 μm (diameter) with a surface area of about 360,000 μm2. So far, the thickness of gold is still thick (> 1 μm). However, putting a few parallel stacked coverslips into the grow solution during the flake synthesis, we did observe formation of extremely thin and large gold flakes in the middle of the stacked coverslips. These results shows that the synthesis of gold nanostructure can be affect by the local flowing of the reactant. By means of microfluidic channels, we hope to control the thickness of the flakes since the liquid flow is mainly laminar in a micro channel. We believe that this method would be a promising method for produce high quality large gold flakes with controlled thickness.

Keywords: plasmon polaritons, gold flakes, microfludic channels