Hydroxyapatite films obtained by sol–gel and sputtering

Hydroxyapatite (HA) biocoatings were obtained using two different deposition methods: sol–gel and sputtering. A direct comparison of films obtained using different techniques is necessary because of possible formation of multi-phases and components in HA films. HA films were investigated using spectroscopic ellipsometry (SE) as a powerful method to evaluate composition and structural properties of the films. For both types of films, sputtering and sol–gel, a weak dispersion of the refractive index within the wavelength range 0.4–0.7 µm was found. This corresponds to a high energy bandgap and a high optical transparency in the UV–VIS range. The internal porosity varying in a wide range in the sol–gel films was evaluated using a modeling of SE data. Additionally to SE studies, structural, chemical and optical characterizations of the films were performed using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Two absorption bands observed in the wavelength ranges 550–600 cm− 1 and 1000–1200 cm− 1 can be attributed to the major absorption modes associated with HA in agreement with published data. From XPS analysis, the atom ratio Ca/P was found for sol–gel films close to the stoichiometric value 1.67. For sputtering films, a higher Ca/P ratio of about 2.1 was estimated. However, similar FTIR spectra have been recorded for both sputtering and sol–gel films. XRD studies show also similar crystallization conditions by annealing at temperatures higher than 500 °C.