Surface observation of nanotube-formed titanium by anodization in electrolyte containing hydroxyapatite nanoparticles

Abstract

Abstract In this work, surface observation of nanotube-formed titanium by anodization in an electrolyte containing hydroxyapatite nanoparticles was carried out using FE-SEM and analyzed by XPS in order to determine changes in the chemical states of elements through depth profiling. The anodized layer consisted of three regions: (1) a TiO2 layer adjacent to titanium, (2) an intermediate barrier layer of TiO2 nanotubes, and (3) a surface hydroxyapatite [HAp, Ca10(PO4)6(OH)2] layer. The nanotube-formed surface consisted of the anatase TiO2 phase. The HAp layer that formed on the TiO2 nanotube film grew vertically, and the electrodeposited HAp nanoparticles were distributed on the whole surface. From comparative analyses of the depth profile before Ar+ ion sputtering and after 4\u202fkeV Ar+ ion sputtering, the multilayer contained Ti, O, Ca, and P, and showed no noteworthy difference. The Ti-2p, O-1s, Ca-2p, F-1s, C-1s, and N-2s transitions were continuously detected in the multilayer as the sputtering time increased. The dominance of the Ti-2p and O-1\u202fs peaks, both before and after the Ar+ ion sputtering, shows that the surface consists mainly of an oxidized TiO2 layer. The Ca-2p and P-2p peaks were subsequently detected from HAp nanoparticles electrodeposited onto the TiO2 nanotube film during an electrochemical reaction. The chemical states of calcium and phosphate in the multilayer were similar to those in HAp.