Crystalline hydroxyapatite coating by hydrolysis using β-tricalcium phosphate target by pulsed-laser deposition

Abstract

Α β-tricalcium phosphate target was employed to decrease the annealing temperature for crystalline hydroxyapatite coating through a hydrolysis process by pulsed-laser deposition. The crystalline hydroxyapatite content of calcium phosphate coating layers was quantitatively evaluated using Raman spectroscopy and X-ray diffraction, and compared with that of pure polycrystalline powder. Calcium phosphate changes from an amorphous phase to crystalline hydroxyapatite through a crystalline α-tricalcium phosphate phase at around 400 °C under an H2O vapor pressure of 0.1 Torr. The crystalline hydroxyapatite content increases steeply by hydrolysis at 500 °C as the H2O vapor pressure is increased from vacuum to 0.15 Torr, but then decreases somewhat at higher pressure. These results indicate that excessive gas pressure blocks small ablated particles such as atoms, ions, molecules, and clusters that would typically be completely hydrolyzed instantaneously following deposition on the substrate.