Fig. 1. The properties of the black TiO₂ film.

(A) Schematic picture for the transition process between conventional TiO₂ and black TiO₂. The insets show the corresponding microscope images of TiO₂ films. (B) Dashed, solid, and dash-dotted lines are the absorption spectra of TiO₂ film before and after 4-min H⁺ ion implantation and the recovered TiO₂ film. (C) and (D) show the refractive index n and light extinction coefficient k as a function of ion implantation time.