Figure 3. AHS-TI consisted of 1.0 µm carbonate-apatite and underlying layered structures. XPS wide-scan spectra of the surfaces of (A) TI (polished titanium), (B) A-TI (alkali-treated titanium), (C) AH-TI (alkali-heat-treated titanium), and (D) AHS-TI (alkali-heat-treated titanium soaked in SBF) (representative case). Note: The chemical composition (at%) of each element is also depicted (mean ± SD, n = 5). (E) The depth profile of AHS-TI (n = 1). Note: AHS-TI consisted of 5 distinctive layers. From the surface, the apatite layer continued with a thickness of about 1.0 µm. Below the first graded zone, there is a Ti-O layer presumably consisting of titanium and TiO₂ oxide about 1.0 µm thick. Below the second graded zone, there is base metallic titanium.