The Preparation And Property Studies Of NiO, TiO₂ And ZnO Films By Magnetron Sputtering

In recent years, NiO, TiO2 and ZnO films have attracted great research interest because of their excellent properties and potential applications. In this work, the NiO, TiO2 and ZnO films were prepared by magnetron sputtering, respectively. The properties of these films were studied, and the influences of deposited and thermal treatment conditions on these films were investigated. A new method for preparing the single layer Ni nanoparticles and NiO nanoparticles with good size uniformity was used in the experiment. The main content and innovation results are as follows:(1) NiO films were deposited on Si by a DC reactive magnetron sputtering in a gas mixture of oxygen and argon. The ratio between the flow rates of oxygen and argon was respectively set at 1:4,1:2, and 1:1. The structures and optical properties of NiO films were investigated using grazing incidence X-ray diffraction and spectroscopic ellipsometry. Ni-rich NiO films were obtained when the ratio between the flow rates of oxygen and argon was 1:4 and 1:2 during the sputtering process. When the ratio reached 1:1, a relatively pure NiO film was formed. The partial pressure of oxygen could significantly influence the thickness and roughness of films. Refractive index n, extinction coefficient k, direct gap energy and indirect gap energy, and the resistance switching characteristics of the NiO films were also studied and depended on the partial pressure of oxygen. The influences of deposition temperature to the NiO films were also investigated by X-ray diffraction.(2) Single layer uniform Ni nanoparticles were prepared by annealing NiO films in hydrogen. The spherical Ni nanoparticles are monodisperse distributed on substrate. The nanoparticle size can be precisely controlled by changing the magnetron sputtering time, and formation process of Ni nanoparticles was investigated systematically. Morphology of these nanoparticles was observed with scanning electron microscope. The compositions of these particles were confirmed by X-ray diffraction pattern. The oxidation coating of Ni nanoparticles was confirmed by transmission electron microscope. Superparamagnetism of Ni nanoparticles was studied by vibration sample magnetometer. The blocking temperature and particle size were calculated by fitting the relationship between coercivity and temperature. The effective anisotropy constant was also obtained by this method, and its value is larger by an order of magnitude than bulk Ni. The origin of such large effective anisotropy could be partly due to the "core-shell" particle structure where the NiO coating interact strongly with the Ni core ("interface effect") and partly due to the marked contribution of the surface anisotropy ("surface effect") which are expected in nanoparticles. Moreover, the NiO nanoparticles were prepared by annealing Ni nanoparticles in oxidation atmosphere. The structures and morphology of these NiO nanoparticles were also studied by X-ray diffraction and scanning electron microscope.(3) TiO2 thin films were deposited on quartz substrates by DC reactive magnetron sputtering of a pure Ti target in Ar/O2 plasma at room temperature. The TiO2 films were annealed at different temperatures ranging from 300 to 800℃in tube furnace under flowing oxygen gas for half an hour respectively. The effect of annealing temperatures on the structure, optical properties and morphologies were presented and discussed by using X-ray diffraction, optical absorption spectrum and atomic force microscope. The films show the presence of diffraction peaks from the (101), (004), (200) and (105) lattice planes of the anatase TiO2 lattice. The direct band gap of the annealed films decreases with the increase of annealing temperature. While, the roughness of the films increases with the rise of annealing temperature, and some significant roughness changes of the TiO2 film surfaces were observed after the annealing temperature reached 800℃. Moreover, the influences of annealing on the microstructures of the TiO2 film were investigated by in situ observation in transmission electron microscope. The photocatalytic properties of the TiO2 film annealed at different temperature were researched.(4) ZnO films were deposited by a RF magnetron sputtering on different substrates. Some novel structures were observed on the surfaces of the films which were deposited on quartz and glass. The film with the (Ni/ZnO)n sturctures were tried to prepared. Though the multi-layer structures were not existed in the samples, a large negative magnetoresistance was also obtained.