Bonelike polycrystalline hydroxyapatite (HAp) thin films were prepared by low temperature hydrothermal annealing from amorphous calcium phosphate films synthesized by sputtering method. The surface properties of the thin films were investigated by X-ray powder diffractometry (XRD), infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS). The biocompatibility was histologically evaluated by bone tissue reaction. The precursory amorphous coating were deposited on titanium with a rf-magnetron sputtering apparatus using calcium phosphate (CP) glass targets in an Ar/CO_2 gaseous atmosphere. The Ca/P ratio of deposited HAp films was controllable in a ranging from 1.50 to 1.67 by adjustment of the chemical composition for CP glass target. The polycrystalline thin films were formed by the hydrothermal post-annealing at above 140 deg C. The post-annealed films were identified as carbonated calcium hydroxyapatite by XRD, IR and XPS. The CO_3~(2-) ions occupied the PO_4~(3-) site of the apatite structure. It was concluded that the bonelike HAp thin films contained CO_3~(2-) ions and were endowed with the outstanding biocompatibility.
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