Broadband highly transparent sapphires with biomimetic antireflective compound submicrometer structures for optical and optoelectronic applications

We reported the broadband highly transparent sapphires with biomimetic antireflective compound submicrometer structures (c-SMSs) made of disordered nanocone arrays on closely packed ordered hemispherical submicrometer gratings (o-SMGs). The o-SMGs and nanocones were fabricated using the spin-coated silica spheres and thermally dewetted gold (Au) nanoparticles, respectively, as the etch masks by a dry etching. The silica spheres with an average diameter of ∼700 ± 10 nm were synthesized. The dot-like Au nanoparticles were formed from the Au thin films with different thicknesses by a proper heat treatment. The total and diffuse transmission characteristics of the fabricated c-SMSs on sapphires were investigated at wavelengths of 350-1100 nm, together with theoretical predictions using a rigorous coupled wave analysis simulation. For the c-SMSs with taller and larger nanocone arrays at 7 nm of Au film, an average total transmittance (T_avg) of ∼90.7% was obtained, exhibiting haze ratios (H) of ∼33.3 and 26% at λ = 525 and 635 nm, respectively. These values were much higher than those of bare sapphire (i.e., T_avg ∼85.4%, H ∼ 5.4 and 3.7% at λ = 525 and 635 nm, respectively). The surface of fabricated c-SMSs also exhibited a strong hydrophilic property with a low water contact angle of ∼10°.