title: Black metal thin films by deposition on dielectric antireflective moth-eye nanostructures.
abstract: Although metals are commonly shiny and highly reflective, we here show that thin metal films appear black when deposited on a dielectric with antireflective moth-eye nanostructures. The nanostructures were tapered and close-packed, with heights in the range 300-600 nm, and a lateral, spatial frequency in the range 5-7 μm(-1). A reflectance in the visible spectrum as low as 6%, and an absorbance of 90% was observed for an Al film of 100 nm thickness. Corresponding experiments on a planar film yielded 80% reflectance and 20% absorbance. The observed absorbance enhancement is attributed to a gradient effect causing the metal film to be antireflective, analogous to the mechanism in dielectrics and semiconductors. We find that the investigated nanostructures have too large spatial frequency to facilitate efficient coupling to the otherwise non-radiating surface plasmons. Applications for decoration and displays are discussed.
authors.affiliation: Department of Micro and Nanotechnology, Technical University of Denmark, Oersteds Plads, Building 345B, DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Alexander B
authors.initials: AB
authors.lastname: Christiansen
authors.affiliation: Department of Micro and Nanotechnology, Technical University of Denmark, Oersteds Plads, Building 345B, DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Gideon P
authors.initials: GP
authors.lastname: Caringal
authors.affiliation: Department of Photonics Engineering, Technical University of Denmark, Oersteds Plads, Building 343 DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Jeppe S
authors.initials: JS
authors.lastname: Clausen
authors.affiliation: Department of Applied Physics, The Benin School of Engineering and Computer Science, The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
authors.forename: Meir
authors.initials: M
authors.lastname: Grajower
authors.affiliation: Nanonics Imaging Ltd., Hartum 19, Har Hotzvim, Jerusalem 97775, Israel.
authors.forename: Hesham
authors.initials: H
authors.lastname: Taha
authors.affiliation: Department of Applied Physics, The Benin School of Engineering and Computer Science, The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
authors.forename: Uriel
authors.initials: U
authors.lastname: Levy
authors.affiliation: Department of Photonics Engineering, Technical University of Denmark, Oersteds Plads, Building 343 DK-2800 Kgs. Lyngby, Denmark.
authors.forename: N Asger
authors.initials: NA
authors.lastname: Mortensen
authors.affiliation: Department of Micro and Nanotechnology, Technical University of Denmark, Oersteds Plads, Building 345B, DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Anders
authors.initials: A
authors.lastname: Kristensen
mesh_terms: D008670:Metals; D008855:Microscopy, Electron, Scanning; D049329:Nanostructures; D013499:Surface Properties
chemical_list: D008670:Metals