Controlled synthesis of hydroxyapatite-based coatings for biomedical application

Here we report the controlled synthesis of hydroxyapatite (HAP) HAP/Ti–alloy composite thin films using pulsed laser deposition (PLD) technique. A KrF excimer laser (wavelength 248 nm, 25 ns pulse duration, 2–3 J/cm2) was used to grow thin films at a base vacuum of ∼ 10− 6 mbar, and substrate temperatures ranging from room temperature to 500 °C. Films were deposited on Si (100) and Sapphire (0001) single crystal substrates. Selected films were annealed in air at 400 °C, or nitrogen/water vapor at 550 °C to study crystallization properties. Fourier transform infrared ipectroscopy (FTIR), x-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDS), and atomic force microscopy (AFM) characterization techniques were employed in the study of the films after deposition and after annealing. All as-deposited thin films were amorphous as seen by XRD and FTIR. AFM showed all films contained micron sized particles embedded into them. Density distribution and size of embedded particles was found to be much less for HAP/Ti–alloy composite thin films compared to pure HAP Films. In between the embedded particles the films were quite smooth. Root mean squared (RMS) roughness of pure HAP films was ∼ 100 nm and decreased to ∼ 50 nm as Ti–alloy content increased. Film roughness in between particles remained smooth to within 1 nm. Annealing of thin films on Si (100) at 400 °C in air resulted in very limited crystallization. However, annealing of thin films on sapphire at 550 °C in nitrogen/water vapor resulted in significant crystallization as seen in both XRD and FTIR with the added features of probable texturing resulting in the prominent presence of (002), and (112) diffraction peaks.