title: Grass-like Alumina with Low Refractive Index for Scalable, Broadband, Omnidirectional Antireflection Coatings on Glass Using Atomic Layer Deposition.
abstract: We present a new type of nanoporous antireflection (AR) coating based on grass-like alumina with a graded refractive index profile. The grass-like alumina AR coating is fabricated using atomic layer deposition (ALD) of alumina and immersion in heated deionized water. Optical transmittance of 99.5% at 500 nm was achieved with average transmittance of 99.0% in the range of 350-800 nm at normal incidence for double-sided coated glass. Angular spectral transmittance (0-80°) of the double-sided AR coated glass was also measured in the range of 350-800 nm and found to have mean spectral transmittance of 94.0% at 60°, 85.0% at 70°, and 53.1% at 80° angles of incidence, respectively. The grass-like alumina AR coating is suitable for mass production with the presented technique: even hundreds of optical components can be coated in parallel. Furthermore, as an ALD-based technique, the coating can be deposited conformally on surfaces with extreme topography, unlike many spin-coating, physical vapor deposition or glancing angle deposition-based coatings used today.
authors.affiliation: Department of Micro- and Nanosciences, Micronova, Aalto University , P.O. Box 13500, FI-00076 Aalto, Finland.
authors.forename: Christoffer
authors.identifier: http://orcid.org/0000-0002-2850-2702
authors.initials: C
authors.lastname: Kauppinen
authors.affiliation: Department of Micro- and Nanosciences, Micronova, Aalto University , P.O. Box 13500, FI-00076 Aalto, Finland.
authors.forename: Kirill
authors.initials: K
authors.lastname: Isakov
authors.affiliation: Department of Micro- and Nanosciences, Micronova, Aalto University , P.O. Box 13500, FI-00076 Aalto, Finland.
authors.forename: Markku
authors.initials: M
authors.lastname: Sopanen
keywords: ALD; alumina; antireflection; atomic layer deposition; broadband; graded index; nanoporous; omnidirectional