Mechanism of apatite formation on silicon suboxide film prepared by pulsed metal vacuum arc deposition

Pulsed metal vacuum arc deposition technology was employed to fabricate SiOx (x ≤ 2) film at the oxygen partial pressure at 0.6 × 10−2 Pa. Surface characteristics of the as-deposited SiOx film were studied by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Results show that the film is substoichiometric and abundant oxygen vacancies exist in the film. The as-deposited film was immersed in simulated body fluid (SBF) for evaluation of in vitro bioactivity. After incubation in SBF, ball-like apatite particles were found on the film surfaces by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The mechanism of apatite deposition on the SiOx film was explained in terms of the silanol functional groups formed on the surface of the film after immersion in SBF. There are abundant active oxygen vacancies in the SiOx film that were attacked by the water molecules in the solution and then formed silanol groups in the film. The silanol groups adsorbed calcium and phosphate ions from the solution to the hydrated surface to form critical apatite cluster. Once the apatite nuclei are formed, they spontaneously grow by consuming calcium and phosphate ions in the surrounding fluid.