The influence of target stoichiometry on the surface properties of sputter deposited calcium phosphate thin films

A range of calcium phosphate (Ca-P) coatings have been sputter deposited at low deposition power from Ca-P targets with different phase compositions. The resultant surfaces were analysed both before and after post-deposition annealing (PDA) using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). The as-deposited surfaces were found to be amorphous in nature and had Ca/P ratios lower than that for their precursor target materials. After PDA at 500 °C, the FTIR and XRD data indicated that the coatings were all hydroxyapatite (HA) in nature. However, the Ca/P ratios were seen to increase significantly, with values above that of their starting precursor target material. It is evident that the Ca/P ratio of the different surfaces, both before and after PDA, are dependent upon the phase composition and stoichiometry of target material. This study has shown the utility of varying the precursor target material in order to modify the resultant surface conditions.