Moth eye inspired hollow sphere ZnO nanostructured layer for broadband antireflection

We report a record low average specular reflectance of 1.6% in the wavelength region of 300-900 nm with hollow sphere zinc oxide (ZnO) nanostructured layer on silicon (100) substrates. The hollow sphere ZnO layer was fabricated using a monolayer of sacrificial self-assembled polystyrene spheres on silicon or glass substrates and subsequent deposition of ZnO by RF sputtering at a typical substrate-target angle of 66° with substrate rotation at 20 rpm. Highly uniform and hexagonal close packed ordering of the ZnO hollow sphere layers over a large area on the substrates was obtained. Each ZnO hollow sphere was found to be hexagonally shaped and structured with 10 nm nipple nanostructures. The average reflectance observed for 5 min. deposition of ZnOwas 3.9 % that decreased with increase in deposition time, down to 1.6 % for 15 min. deposition. This type of hollow sphere ZnO layers can be applied as broadband antireflection layers for photo-devices.