A method of fabricating c-axis-oriented hydroxyapatite film on a quartz crystal microbalance (QCM) sensor was investigated. ZnO was used as a template to obtain a hexagonal hydroxyapatite crystal of uniaxial orientation. The ZnO was grown as a c-axis film on a Au/quartz with the surface structure of a QCM sensor. Under optimized conditions, hydroxyapatite was deposited by pulsed laser deposition. X-ray diffraction showed the hydroxyapatite film to be oriented along the c-axis. Because Au and ZnO are applied to many devices, the anisotropic properties of hydroxyapatite may be incorporated into these devices as well as QCM sensors. #
A technique to control the crystallinity of hydroxyapatite (HA) was investigated for applications such as dentistry, regenerative medicine, cell culture scaffolding, and bio-sensors. An amorphous HA film was first produced by pulsed laser deposition. After deposition, it was separated from a substrate as a free-standing sheet. Annealing was then performed to control the crystallinity of the sheet. It was found that conventional annealing in an electric oven was not suitable for HA sheets, because it led to curling and cracking. Since such problems were assumed to be caused by thermal stress, annealing was next carried out with the HA sheet enclosed in HA powder in the center of a metal capsule. This method allowed annealing to be successfully carried out without causing any curling or cracking. Uniform pieces with dimensions of 10 mm × 10 mm cut from a large HA sheet were annealed at temperatures of 200 to 800 ºC and then examined using X-ray diffraction. It was found that the intensity of the diffraction peaks associated with crystalline HA changed with annealing temperature, and that the strongest peaks were observed for the sample annealed at 500 ºC. These results indicate that the crystallinity of the HA sheet can be controlled using the proposed method.
The relation between O 2 pressure and composition in the pulsed-laser deposition of fluoroapatite was investigated using both on-axis and off-axis methods to determine the optimal conditions for obtaining a pure fluoroapatite film without OH groups. Through this, it was found that an O 2 pressure of 10 Pa, combined with an off-axis method, results in P/Ca and F/Ca values (0.6 and 0.2, respectively) that match closely with a stoichiometric composition of Ca 10 (PO 4 ) 6 F 2 . Fourier transform infrared spectroscopy analysis confirmed that this optimized film was almost pure fluoroapatite, with no evidence of any OH groups originating from hydroxyapatite. X-ray diffraction also revealed that this fluoroapatite film crystallizes with a c-axis orientation perpendicular to its surface.
Pulsed laser deposition using a sintered (700 °C) mixture of Ca3(PO4)2 and CaF2 produces Ca10(PO4)6F2 films without OH groups at an O2 pressure of 10 Pa, combined with an off‐axis method.
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