Low temperature growth of ZnO nanostructures on flexible polystyrene substrates for optical, photoluminescence and wettability applications

Abstract

The growth of ZnO nanostructures on flexible polystyrene substrates by a simple vacuum thermal evaporation process is reported. The ZnO films are deposited on polystyrene surfaces of 6 m thickness which are initially anchored on glass substrates. The as-deposited films are annealed at temperatures up to 180 °Cfor 6-24 h after which the polystyrene is lifted off from the glass substrates to yield nanostructured films on a flexible substrate. At 180 °Cthere is transformation of the partially oxidized as-deposited films into nearly stoichiometric ZnO. This is accompanied by the formation of nanostructures such as nanorods, nanotubes and nanodoughnuts. The films, which were 50-200 nm in thickness, are polycrystalline in nature and also exhibit Zn/ZnO core-shell structures under favorable conditions. The nanostructures exhibit transmission greater than 80% in the visible and near infrared regions and band gaps of the order of 4 eV. The films exhibit strong blue photoluminescence and the peak position as well as intensity of emission can be tuned by varying thickness and annealing conditions. To demonstrate the flexibility, the ZnO coated polystyrene substrates were wrapped around a LED to showUVblocking property. Wettability studies indicate that films are hydrophobic with water contact angles between 92°-95°.