Anodic titania nanotubes (ATNTs) have recently attracted particular attention due to their ease of preparation, low cost, large surface area, alignment and self-ordering. Especially, ATNTs are of interest for a wide variety of applications, including dye-sensitized solar cells, electrochemical sensors, photocatalysts, supercapacitors, etc. However, compared with analogous porous anodic alumina, the synthesis of ATNTs with regular and controllable microscopic morphologies is still under development. Although a number of excellent reviews on ATNTs have appeared, most of them have generally focused on their formation mechanism, properties, modifications and applications. This review attempts to pay close attention to the controllable fabrication of ATNTs, i.e., length, tube diameter, and self-ordering of nanotubes can be adjusted over large length scales. The preparation techniques of ATNTs in the last decade are summarized and the key factors for synthesis of ATNTs with tunable morphologies are discussed. In this review, we first present the anodization conditions of fabricating conventional ATNTs in ethylene glycol (EG) electrolytes and the typical microscopic morphologies of as-obtained ATNTs. Then, we discuss the growth characteristics and morphological parameters of ATNTs anodized in other electrolyte systems, such as aqueous solution, glycerol, dimethyl sulfoxide. It has been demonstrated that anodization conditions, including the solvent, temperature, anodization voltage, anodization duration and F^- concentration, have profound effects on the morphologies of ATNTs. On the basis of these experimental findings, we overview how to adjust tube diameter, tube length, wall thickness and self-organization of ATNTs by changing anodization parameters. Some fabrication methods for nanotubes with a length of over several hundreds micrometers and the structural features of such thick ATNT films are also given. In addition, the strategies to detach as-formed ATNTs from the metallic substrate and to obtain free-standing ATNT membranes are described. Finally, we emphasize some related issues for fabrication of ATNTs with tunable morphologies and indicate the main challenges and potential future directions of the field.

Contents
1 Introduction
2 Anodization conditions of fabricating the conventional ATNTs
3 ATNTs grown in non-ethylene glycol (EG)-based electrolyte systems
4 Adjustment of tube diameter and ordering of ATNTs
4.1 Adjustment of tube diameter
4.2 Achievement of an improved ordering for ATNTs
5 Methods for fabricating ATNTs with ultralong nanotubes
6 Strategies to obtain free-standing ATNT membranes
7 Conclusion