In this study, we combined atomic layer deposition and anodic aluminum oxide (AAO) on a silicon substrate and developed self-aligned TiO2 nanotube arrays. We studied the growth mechanism of TiO2 nanotubes on the inner wall of AAO at 100 and 400 degrees C. We found that at 100 degrees C, TiO2 grew in a layer-by-layer manner. Therefore, it can be grown into TiO2 nanotube arrays with very thin walls. However, at 400 degrees C, TiO2 needs to first form a 2.5-nm amorphous layer, before becoming crystalline TiO2 via a phase transformation, and growing into crystalline TiO2 nanotube arrays along the preferred plane {101} by means of a space-limited growth mechanism. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3528939] All rights reserved.