Chemical state and ultra-fine structure analysis of biocompatible TiO ₂ nanotube-type oxide film formed on titanium substrate

TiO₂ nanotube-type oxide film on Ti substrate has been fabricated using an electrochemical method, and the chemical bonding state, ultra-fine structures, and surface characteristics of the TiO₂ nanotube layer have been investigated. The formation and growth of a self-organized nanotube layer can be achieved directly by anodization in NH ₄-containing electrolytes. The diameter, length, and wall thickness of the nanotube are significantly affected by anodizing conditions such as applied voltage, current density, and anodizing time. The length limiting factor of nanotube growth was found to be the diffusion of ionic species in the electrolyte. XRD investigations revealed that annealed nanotubes have anatase and rutile structure, and some Ti-peaks from the Ti substrate were observed. From the compositional analysis of TiO₂ nanotubes layer using Energy Dispersive Spectroscopy (EDS), Ti, O, and P elements were obtained in the wall nanotube layer. For incorporated P-containing in the TiO₂ nanotube layer, various chemical states were presented, which were revealed mostly in the forms of H₂PO₄, HPO₄^2-, and PO ₄^3-.