Fabrication And Characterization Of The Niobium(Tantalum) Oxide Films

Oxide thin films with structural color have broad application prospect in the fields of anti-counterfeiting,decoration and sensor due to bright color,high saturation,friendly environment and easily controllable wavelength.Anodic oxide films prepared by anodic oxidation method have outstanding advantages such as simple in preparation,convenient to control process conditions and wide practical application.For example,porous anodic alumina(PAA)films not only have controllable structural color,but also regular close-packed hexagonal pattern and uniform arranged pores.Expect for structural color,many other physical properties such as ferromagnetism and resistance property are induced by the structure of PAA films.It's found that these properties are closely related to porous structure.On this basis,niobium oxide films and tantalum oxide films with ordered porous structure have been prepared by anodic oxidation method.Structure and physical properties of these films have been researched by using a variety of characterization methods.The details are as follows:(1)After niobium foils were pretreated,niobium oxide films with structural color were prepared by one anodic oxidation at room temperature.The color saturation and wavelength range of a series of niobium oxide films can be tuned by changing the oxidization voltage.The thickness of films increases with the increase of voltage at the same time.Based on the experimental results,the mechanisms of color generation about niobium oxide films are analyzed.When the thickness of films is less than 150 nm,structural color is caused by the scattering of light,which conforms the principle of complementary color.While the thickness of films is more than 150 nm,structural color comes from the interference of light,which conforms Bragg equation.Ordered porous niobium oxide films were prepared in electrolytic solution by two-step anodic oxidation method.The depth of holes increases with the increase of voltage in the experiment.Meanwhile,the phenomenon of groove connection appears on the surface of films.From the measurements of magnetism,room temperature ferromagnetism is found in porous niobium oxide films under different conditions.The magnetization along the out-of-plane direction is much larger than which along the in-plane direction.The magnetization of niobium oxide films is gradually decreased when lengthening annealing time in air.These phenomena indicate the changes of magnetization are related to oxygen vacancy.(3)Structure and properties of a series of porous tantalum oxide films obtained by two-step anodic oxidation method at room temperature can be characterized.It is found from the results of characterization that the behavior of all porous tantalum oxide films is room temperature ferromagnetism and the magnetization along the out-of-plane direction is much larger than which along the in-plane direction.Compared with the magnetization of as-prepared tantalum oxide films,the magnetization of films after vacuum annealing can increase,but the magnetization of films at the same annealing time in air decreases.Furthermore,the magnetization gradually decreases with extension of annealing time in air.These phenomena show that the tantalum oxide films exhibit room temperature ferromagnetism,which futher proves the oxygen vacancy concentration affects magnetic property of films.