The Influence of argon gas pressure on co-sputtered calcium phosphate thin films

A series of Ca–P coatings have been co-deposited by RF magnetron sputtering from hydroxyapatite targets at a range of different argon gas pressures (1–5 Pa) at a low discharge power level. The resultant surfaces were analysed both as-deposited and after annealing at 500 °C using fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and stylus profilometry. The deposition rate increased with increasing argon gas pressure up to 2 Pa, but decreased significantly as the pressure increased up to 5 Pa. The Ca/P ratios of the as-deposited coatings were lower than expected, and decreased significantly at the higher argon gas pressures. The corresponding FTIR and XRD data showed that the as-deposited surfaces were poorly hydroxylated and were mostly amorphous in nature. By comparison, the annealed surfaces had Ca/P ratios of between 3.38 ± 0.11 (1 Pa) and 1.82 ± 0.06 (5 Pa). The FTIR and XRD data for the annealed samples were indicative of HA, however, as the gas pressure increased above 3 Pa, these surfaces were most likely transformed into dehydroxylated HA. This study has shown the utility of varying the argon gas pressure whilst co-sputtering HA in order to modify the resultant surface conditions.