title: Porous anodic alumina with low refractive index for broadband graded-index antireflection coatings.
abstract: Materials with very low refractive index are essential to prepare broadband graded-index antireflection (AR) coatings. However, the availability of such materials is very limited. In this study, large-area (4 cm×4 cm) low refractive index porous anodic alumina (PAA) coatings on glass substrate were prepared successfully by electron-beam evaporation, electrochemical oxidation, and chemical etching method. The nanopore size of PAA film is smaller than 40 nm, and the refractive index of PAA film is n=1.08. Besides, five-layered graded-index broadband PAA coatings with refractive indices following the Gaussian profile were also prepared to noticeably eliminate the reflectance of glass over a broadband wavelength, and the lowest reflectivity is 0.64% at the wavelength of 534 nm at normal incidence. The PAA AR coatings having an omnidirectional nature are likely to have practical applications in photovoltaic cells and optical devices.
authors.affiliation: Ningbo Institute of Material Technology & Engineering, Chinese Academy of Sciences, Ningbo 315201, China.
authors.forename: Junwu
authors.initials: J
authors.lastname: Chen
authors.forename: Biao
authors.initials: B
authors.lastname: Wang
authors.forename: Yi
authors.initials: Y
authors.lastname: Yang
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Shi
authors.forename: Gaojie
authors.initials: G
authors.lastname: Xu
authors.forename: Ping
authors.initials: P
authors.lastname: Cui