Macro, micro and nanostructure of TiO2 anodised films prepared in a fluorine-containing electrolyte

The paper presents an electron microscopy study of the macro, micro and nanostructure of titania nano-tubes formed by electrochemical anodisation of titanium in a fluorine containing electrolyte. Scanning electron microscopy (SEM) is used to examine the overall structure of the nano-tubes formed under potentiostatic conditions. Transmission electron microscopy (TEM) has been used to examine the structure of the oxide layer of a sample anodised for a relatively short period (30 min) and provides a new insight into the formation of titania nano-tubes. The fluorine ions are able to nucleate sites on the titanium metal and generate a series of interconnected cavities or pores in the oxide complex formed, allowing current to flow within this film. Under specific conditions the cavities and randomly dispersed pores can align in the direction of the applied electric field and link up to generate an array of tubes, where the passage of ions and water is optimised. We also suggest that oxygen evolution at the anode may play a role in the development of the nano-tubes.