Vacuum ultraviolet annealing of hydroxyapatite films grown by pulsed laser deposition

The effect of a post-deposition vacuum ultraviolet (VUV) radiation-assisted annealing treatment performed under 1 bar of oxygen at moderate temperatures (450 °C) upon thin hydroxyapatite (HA) films grown by the pulsed laser deposition technique was investigated. The HA layers were deposited at 650 °C under different partial oxidizing pressures without any water vapor and exhibited, besides the HA crystalline phase, tetracalcium phosphate and calcium oxide phases, more so for the films grown at lower oxidizing pressures. After the VUV-assisted anneal the layers were transformed into high quality crystalline HA films, exhibiting Ca/P ratio values closer to 1.67, the value for stoichiometric HA. The content of the other crystalline phases initially present was reduced significantly. Infrared spectroscopy also showed that the amount of ${\mathrm{OH}}^{\mathrm{-}}$ in the films increased after the treatment. The combination of these two low temperature techniques opens the possibility of growing high quality HA layers without significant oxidation of the substrate material.