Preparation, optical properties, and color formation mechanism of tantalum oxide anode films

Tantalum oxide films with a high-color-saturation structure were successfully prepared by anodization in a phosphoric acid electrolyte at a voltage of 100 V. It was shown by using field-emission scanning electron microscopy that the films exhibited a compact and uniform structure, and their granular surface was conducive to light scattering and improving color saturation. Interestingly, the film color could be randomly adjusted only by changing the anodization time. The thickness of the oxide film increased with the anodization time. Thus, the change of the film color was directly related to the film thickness. According to the different characteristics of their UV–Vis spectra, the films were divided into three categories to explain the color formation mechanisms in terms of the thickness change. Tantalum oxide films can be applied for anti-counterfeit decoration according to color adjustability and the angle effect.