Microstructure of hydroxyapatite thin layers grown by pulsed laser deposition

Thin films of hydroxyapatite (HAp) have been grown on Si, quartz, Ti, and Ge substrates by the pulsed laser deposition (PLD) method employing a KrF excimer laser (wavelength lambda=248 nm, pulsed duration tau FWHM=20 ns). The influence of the laser deposition parameters on the properties of the grown layers was investigated in order to optimise the Ca/P ratio and the crystalline structure. It was found that the optimum conditions for preserving the Ca/P ratio i.e. high oxygen pressures and low substrate temperatures do not coincide with those for obtaining adherent and crystalline layers i.e. low oxygen pressures and high substrate temperatures. For films deposited onto Ti substrates it was also found that high substrate temperatures promote the diffusion of Ti through the depositing film up to the surface where it gets oxidised. Further investigations are required before high quality HAp-coated Ti implants by PLD can be obtained.