Free-Standing Porous Anodic Alumina Templates for Atomic Layer Deposition of Highly Ordered TiO₂ Nanotube Arrays on Various Substrates

Abstract

Free-standing porous anodic alumina (PAA) templates are used for fabrication of dense, uniform, highly ordered, and well-aligned arrays of TiO 2 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. TiO 2 nanotube arrays with atomic layer control of wall thickness are prepared via ALD on the template. The TiO 2 nanotube arrays with varying wall thickness show size-dependent optical adsorption behaviors. Anatase TiO 2 nanotubes are formed by annealing in air above 300 °C. Our method can easily create highly ordered TiO 2 nanotube arrays on a wide range of substrates without causing chemical contamination and changing surface morphology on the substrates. The prepared TiO 2 nanotube arrays show good contact with the substrate, which is of great importance in device applications.