Fabrication and Characterization of High-Crystalline Nanoporous ZnO Thin Films by Modified Thermal Evaporation System

The aim of this work is to fabricate high-crystalline nanoporous zinc oxide (ZnO) thin films by a modified thermal evaporation system. First, zinc thin films have been deposited on bare glass substrate by the modified thermal evaporation system with pressure of 0.05 mbar, source-substrate distance of 3 cm and source temperature 700 degrees C. Then, high-crystalline ZnO thin film is obtained by annealing at 500 degrees C for 2 h in atmosphere. The prepared ZnO films are characterized with various deposition times of 10 min and 20 min. The structural property was investigated by X-ray diffractometer (XRD). The optical bandgap and absorbance/transmittance of these films are examined by ultraviolet/visible spectrophotometer. The surface morphological property has been observed by scanning electron microscope (SEM). ZnO films have showed uniform nanoporous surface with high-crystalline hexagonal wurtzite structure. The ZnO films prepared with 20 min has excitation absorption-edge at 369 nm, which is blueshifted with respect to the bulk absorption-edge appearing at 380 nm. The gap energy of ZnO film is decreased from 3.14 eV to 3.09 eV with increase of the deposition time, which can enhance the excitation of ZnO films by the near visible light, and is suitable for the application of photocatalyst of waste water cleaning and polluted air purification.