Preparation And Properties Of Nickel Oxide Thin Films

Nickle oxide?NiO?with cubic structure is a semiconductor with wide band gap,which is 3.6-4.0 eV at room temperature.NiO thin films are believed to have potential in the fields of gas sensors and electrochromism.On the other hand,NiO receives attention in photocatalysis in recent years.This dissertation focused on the growth behavior and optical and electric properties of NiO films deposited by reactive magnetron sputtering method and the ambient pressure,growth temperature and the substrate type were explored.Based on the growth of NiO films,we found abnormal oxidation of Ag films by reactive deposition of NiO,and then the photocatalysis of the oxidized Ag films was further studied.The main conclusions are summaried below.During the deposition of NiO films by reactive magnetron sputtering method,the working pressure has impacts on the preferred orientation of NiO films.At 400°C and 40:10 of Ar to O₂ ratio of gas flow,the NiO films deposited at 5.0 Pa are highly?100?-textured.With the decrease in the ambient pressure,the preferred orientation of Ni O films changed to be?111?,with the decrease in the transmittance and the resistivity.Growth temperature is another important factor that influences the growth and crystal quality of NiO films.At 1.0 Pa with 40:10 of Ar to O₂ ratio of gas flow,the Ni O films deposited at room temperature are highly?100?-textured.With the increase in growth temperature,the preferred orientation of NiO films changed to be?111?,with the increase in the transmittance and the resistivity.At 700 °C,the NiO films changed to be?110?-textured on the quartz substrate,probably in association with the phase transition of cubic to hexagonal phase.Using the reactive magnetron sputtering method,highly-epitaxial NiO films were successfully grown on MgO single-crystal substrate at 400 and 700 °C.The highly-expital NiO films exhibited good optical properties and photoluminescence of band-gap transition.During deposition of NiO by reactive magnetron-sputtering method,the Ag films were found to be oxidized abnormally.The Ag films were oxidized layer by layer from the top to the bottom,with the oxidation rate as high as 60 nm/min at the specific condition for deposition of NiO.The oxidation of Ag films is rather abnormal because no NiO films formed on the sample surface.In addition,the Ag films were first oxidized into h-Ag₂ O films,and then into c-Ag₂ O films.Sufficient length of deposition time will lead to formation of nanofiber c-Ag₂ O films.The oxidized Ag films exhibited excellent performance in photocatalysis,much better than that of crystalline TiO₂?c-TiO₂?films.Under the UV irradiation,the photocatalytic activity of Ag₂ O films is 2.8⁴.7 times that of c-TiO₂ films.Under the irradiation of visible light simulating sunlight,the photocatalytic activity of Ag₂ O films is 4.3⁶.3 times that of c-TiO₂ films.Among the Ag₂ O films,the nanofiber Ag₂ O films exhibited the highest photocatalytic activity.