Gold Metasurfaces for Light Absorption Enhancement via Block Copolymer Lithography

Optical properties of metals are often characterized by high reflectance and losses. Recently, “total“ optical absorption in metal films has been of interest in applications such as biosensing, nonlinear optics and solar energy harvesting. Attempts to enhance the absorption have been made by depositing lossy dielectric or semiconductor thin films or nanostructuring the surface [1]. Here we have combined block copolymer lithography (BCP) with a template stripping process to create metasurfaces that exhibit strong light absorption in the visible range.An inverse pattern was etched onto a Si wafer using a mask made from poly(styrene-vinylpyridine) as described previously [2]. A thin layer of Au was deposited on the patterns and a support was attached on top using UV-curable epoxy. Due to the poor adhesion of Au on Si, the top layers could be cleanly separated from the Si mold revealing a high-quality nanostructured Au film.BCP lithography can produce sub-wavelength structures over large areas with ease and template stripping enables the transfer of patterns onto a variety of rigid, flexible and curved substrates. The Au films could absorb > 95% of light up to 550 nm, which could also be seen as altered coloring. We expect to incorporate the material into sensor surfaces and plasmonic devices that generate energetic hot electrons.
(1) Kats M, Capasso F, Las. Photon. Rev. 2016;5(735)
(2) Hulkkonen H, Salminen T, Niemi T, ACS Appl. Mater. Interfaces. 2017;9(37)