Annealed zinc oxide films for controlling the alignment of liquid crystals

It is observed that the anchoring of LC molecules aligned on the ZnO film depends on the surface wettability. We demonstrate that the surface wettability of ZnO films fabricated by sol–gel process can be modified by annealing. The observations using the scanning electron microscope, photoluminescence and X-ray photoelectron spectroscopy for ZnO films have shown that the annealing can modify both the morphologies and chemical compositions of ZnO films, which in turn produces influences on the surface wettability. The surface wettability of as-prepared ZnO film can be controlled from 102° to 60° (contact angle (CA) of water) as the annealing temperature increases from 190 to 250 °C. Our experimental results show that the pretilt angles of LCs on ZnO films can be modified over a wide range from 89.5° to 0.5° as the CA of water on the ZnO films changes from 102° to 60°.