MEDICAL DEVICES BASED ON BIOINSPIRED CERAMICS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 383

3. interaction of the plasma plume with the substrate, leading to a large num-
ber of gas phase collisions;
4. nucleation and growth of the coating on the substrate surface, which also
involve many processes such as atomic deposition, re-evaporation, clus-
ter nucleation and growth, species diffusion within the surface and cluster
dissociation.
All these mechanism can be infl uenced by the experimental processing condi-
tions and would infl uence the physicochemical properties of the coatings.
11.4.4 Physico-Chemical Properties of the Hydroxyapatite and
Substituted Apatite Coatings
The pulsed laser deposition method has been successfully applied to the prepara-
tion of high quality crystalline HA coatings on Ti substrates [Cotell, 1993; Arias,
1997; Solla, 2005], enhancing greatly the fi lm properties in comparison with those
obtained by commercial techniques such as plasma spray [García-Sanz, 1997].
Also, silicon substituted apatite [Solla, 2007] coatings have been recently obtained
by laser ablation.
Thin fi lms of hydroxyapatite (HA) and Si substituted hydroxyapatite (Si-
HA) were grown from ablation targets made with different mixtures of commer-
cial carbonated HA and Si powder (0, 2.5, 5, 7.5 and 10% at.), in the presence
of a water vapour atmosphere. The physico-chemical properties of the coatings
and the incorporation of the Si into the HA structure were studied by Fourier
Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD) and X-Ray
Photoelectron Spectroscopy (XPS).
Figure 11.19 shows the FTIR spectra of the coatings, exhibiting the presence
of the main absorption bands corresponding to carbonated hydroxyapatite,
being:
1. 1000 - 1200, 960 and 560 cm − 1 attributed to asymmetric stretching, sym-
metric stretching and asymmetric bending vibrations of PO 3− groups
respectively,
2. 1400 - 1500 and 875 cm − 1 that are assigned to asymmetric stretching and
bending vibration of CO 2− groups respectively, and
3. an absorption at 3575 cm − 1 corresponding to the stretching vibration of the
OH − groups that are present in the HA structure.
With the progressive introduction of the amount of Si in the ablation target, many
differences were observed in the IR spectra:
1. an intense reduction of the intensity of the OH − stretching absorption
band at 3575 cm − 1 ,
2. an evident diminution of the intensity of the CO 2− asymmetric stretching,