Tunable structural color of anodic tantalum oxide films

Tantalum (Ta) oxide films with tunable structural color were fabricated facilely using anodic oxidation. The structure, components, and surface valence states of the oxide films were investigated by using gazing incidence X-ray diffractometry, X-ray photoelectron microscopy, and surface analytical techniques. Their thickness and optical properties were studied by using spectroscopic ellipsometry and total reflectance spectrum. Color was accurately defined using L^*a^*b^* scale. The thickness of compact Ta₂O₅ films was linearly dependent on anodizing voltage. The film color was tunable by adjusting the anodic voltage. The difference in color appearance is resulted from the interference behavior between the interfaces of air-oxide and oxide-metal.