Aligned metal oxide nanotube arrays: key-aspects of anodic TiO2 nanotube formation and properties

摘要

Over the past ten years, self-aligned TiO2 nanotubes have attractedtremendous scientific and technological interest due to their anticipatedimpact on energy conversion, environment remediation and biocompatibility. Inthe present manuscript, we review fundamental principles that govern theself-organized initiation of anodic TiO2 nanotubes. We start with thefundamental question: Why is self-organization taking place? We illustrate theinherent key mechanistic aspects that lead to tube growth in various differentmorphologies, such as rippled-walled tubes, smooth tubes, stacks andbamboo-type tubes, and importantly the formation of double-walled TiO2nanotubes versus single-walled tubes, and the drastic difference in theirphysical and chemical properties. We show how both double- and single-walledtube layers can be detached from the metallic substrate and exploited for thepreparation of robust self-standing membranes. Finally, we show how byselecting the right growth approach to TiO2 nanotubes specific functionalfeatures can be significantly improved, e.g., an enhanced electron mobility,intrinsic doping, or crystallization into pure anatase at extremely hightemperatures can be achieved. This in turn can be exploited in constructinghigh performance devices based on anodic TiO2 in a wide range of applications.