title: Ultra-thin films with highly absorbent porous media fine-tunable for coloration and enhanced color purity.
abstract: We demonstrate ultra-thin, fine-tunable optical coatings with enhanced color purity based on highly absorbent porous media on a metal substrate. We show that the color range provided by these ultra-thin film coatings can be extended by making the absorptive dielectric layer porous. Oblique angle deposition (OAD) of a thin (10-25 nm) germanium (Ge) film by e-beam evaporation onto a thick gold substrate yields controlled porosity. Reflectance spectra and color representations from both calculations and experiments verify the enhancement of resonance tunability and color purity in the nano-tailored coatings. Angle independent reflection properties, and the applicability of such porous Ge on various metal substrates, indicate the strength of these concepts.
authors.affiliation: School of Electrical Engineering and Computer Science, Gwangju Institute of Science and Technology, 123 Cheomdan-gwagiro, Buk-gu, Gwangju 61005, Republic of Korea. ymsong@gist.ac.kr.
authors.forename: Young Jin
authors.identifier: http://orcid.org/0000-0002-6490-2324
authors.initials: YJ
authors.lastname: Yoo
authors.affiliation: Department of Electrical Engineering, Pohang University of Science and Technology, 77 Cheongam-Ro, Nam-gu, Pohang 37673, Republic of Korea.
authors.forename: Jin Ha
authors.identifier: http://orcid.org/0000-0001-8110-2241
authors.initials: JH
authors.lastname: Lim
authors.affiliation: School of Electrical Engineering and Computer Science, Gwangju Institute of Science and Technology, 123 Cheomdan-gwagiro, Buk-gu, Gwangju 61005, Republic of Korea. ymsong@gist.ac.kr.
authors.forename: Gil Ju
authors.initials: GJ
authors.lastname: Lee
authors.affiliation: Department of Robotics Engineering, Daegu Gyeongbuk Institute of Science and Technology, 333 Techno Jungang-daero, Hyeonpung-myeon, Dalseong-gun, Daegu 42988, Republic of Korea. kijang@dgist.ac.kr.
authors.forename: Kyung-In
authors.initials: KI
authors.lastname: Jang
authors.affiliation: School of Electrical Engineering and Computer Science, Gwangju Institute of Science and Technology, 123 Cheomdan-gwagiro, Buk-gu, Gwangju 61005, Republic of Korea. ymsong@gist.ac.kr.
authors.forename: Young Min
authors.identifier: http://orcid.org/0000-0002-4473-6883
authors.initials: YM
authors.lastname: Song