All-Metal Broadband Optical Absorbers Based on Block Copolymer Nanolithography

The growing interest in solar energy during recent years has spurred on the development of high-efficiency optical absorbers using emerging concepts in plasmonics and metamaterials. Most absorber designs require patterning on a subwavelength scale, making large-scale fabrication expensive or impractical. This study presents an all-metal metasurface with tightly packed, sub-80 nm nanodomes fabricated by template-stripping thin gold films from reusable silicon templates. Subwavelength patterning was achieved via molecular self-assembly of block copolymers, which enables large-area, periodic patterning with nanometer precision. The proposed nanodome surface acts as an optical absorber capable of absorbing 97% of incident light in the visible range 320-650 nm, and still more than 90% at high incidence angles. We demonstrate both experimentally and theoretically that the absorption behavior of the thin film can be controlled by changing the size of the nanodomes, namely, the gap between the structures. The enhanced absorption of light is attributed to localized particle plasmon and gap plasmon resonances. This research provides a straightforward and cost-effective strategy to design and fabricate thin, large-area, light-absorbing coatings that can be transferred onto nearly any rigid or flexible substrate. The all-metal metasurfaces are a promising candidate for plasmon-induced hot electron generation for efficient solar energy conversion in photovoltaic and photocatalytic devices.