Free-standing porous anodic alumina templates for atomic layer deposition of highly ordered TiO2 nanotube arrays on various substrates

Free-standing porous anodic alumina (PAA) templates are used for fabrication of dense, uniform, highly ordered, and well-aligned arrays of TiO2 nanotubes on various substrates, including glass, Si, and flexible polyimide films, via atomic layer deposition (ALD). A large-area free-standing PAA template (>4.5 cm(2)) is first attached onto the substrate with support of a protective layer of poly(methyl methacrylate) (PMMA) applied on its top. UV-ozone treatment is then employed to completely remove the PMMA layer, keeping the large-area template intact. TiO2 nanotube arrays with atomic layer control of wall thickness are prepared via ALD on the template. The TiO2 nanotube arrays with varying wall thickness show size-dependent optical adsorption behaviors. Anatase TiO2 nanotubes are formed by annealing in air above 300 degrees C. Our method can easily create highly ordered TiO2 nanotube arrays on a wide range of substrates without causing chemical contamination and changing surface morphology on the substrates. The prepared TiO2 nanotube arrays show good contact with the substrate, which is of great importance in device applications.