EXCIMER-LASER DEPOSITION OF HYDROXYAPATITE THIN-FILMS

We have demonstrated a new and simple in situ method to fabricate adhe rent and dense hydroxyapatite (HA) coatings at relatively low depositi on temperatures (500-600 degrees C). Under optimum processing conditio ns, the HA coatings possess a nominal Ca:P ratio of 1.65 and exhibit a fully crystalline single-phase structure. This deposition technique i s based on the application of a pulsed excimer laser (wavelength lambd a = 248 nm, pulse duration tau = 25 x 10(-9) s) to ablate a dense stoi chiometric HA target. The HA target was prepared by standard ceramic c oprecipitation techniques followed by cold pressing and further sinter ing at 1200 degrees C in air. High substrate temperatures (greater tha n or equal to 600 degrees C) during film deposition led to phosphorus deficient coatings because of re-evaporation of phosphorus during the deposition process. The stabilization of various calcium and phosphoru s phases in the film was controlled by a number of process parameters such as substrate temperature, chamber pressure and presence of water vapour in the chamber. This is particularly advantageous for productio n of HA coatings,since it is known that HA decomposes at high temperat ures due to the uncertainty in the starting material stoichiometry. Ru therford backscattering spectrometry, energy dispersive X-ray analysis , transmission electron microscopy, scanning electron microscopy and X -ray diffraction techniques were employed to determine the structure-p rocessing relationships. Qualitative scratch measurements were conduct ed to determine the adhesion strength of the films.