Figure 3. Representative Fourier transform infrared spectrum of as-sputtered calcium phosphate (CaP) coatings, hydroxyapatite (HA) target, and sputtered CaP coatings after a 400°C heat treatment at different heating times. The different surfaces were (1) no heat treatment (as-sputtered), (2) heat treatment for 1 hr in the absence of water vapor, (3) heat treatment for 2 hrs in the absence of water vapor, (4) heat treatment for 4 hrs in the absence of water vapor, (5) heat treatment for 1 hr in the presence of water vapor, (6) heat treatment for 2 hrs in the presence of water vapor, (7) heat treatment for 4 hrs in the presence of water vapor, and (8) HA target. The arrow indicates the OH peak at 3572 cm^-1, and the asterisk indicates the PO₄ peaks at 1084 cm^-1, 964 cm^-1, 617 cm^-1, 585 cm^-1, and 458 cm^-1.