Structure, elemental composition, and mechanical properties of films prepared by radio-frequency magnetron sputtering of hydroxyapatite

The phase composition, substructure, and surface morphology of 0.1-to 5.0-μm-thick films grown on different substrates by radio-frequency magnetron sputtering of a hydroxyapatite ceramic target are investigated using transmission electron microscopy (TEM), high-energy electron diffraction, X-ray diffraction, IR spectroscopy, Auger electron spectroscopy, ultrasoft X-ray emission spectroscopy, Rutherford backscattering spectroscopy, scanning electron microscopy (SEM), and atomic-force microscopy (AFM). The hardness and adhesion strength of these films are studied using the nanoindentation and scratching methods. It is revealed that the structure of the films depends on the spatial inhomogeneity of the plasma discharge. Single-phase dense nanocrystalline hydroxyapatite films are formed when the substrate is located above the erosion zone. According to the X-ray diffraction, high-energy electron diffraction, and IR spectroscopic data, the structure of the films corresponds to the hydroxyapatite structure. As follows from the Auger electron, ultrasoft X-ray emission, and Rutherford backscattering spectroscopic data, the elemental composition of the films is similar to the stoichiometric composition of hydroxyapatite. The analysis of the X-ray diffraction and AFM data demonstrates that the films have a dense structure. The results of the mechanical tests show that the hardness of the coatings is higher than 10 GPa and that the maximum adhesion strength ( L C = 12.8 N) is observed for the hydroxyapatite coatings on the titanium substrate modified by the TiC-TaC-Ca 3 (PO 4 ) 2 composite layer.