Stoichiometric transfer in pulsed laser deposition of hydroxylapatite

Hydroxylapatite (HA, Ca-10(PO4)(6)(OH)(2)) is a calcium phosphate used as c oating for dental and orthopaedical implants because its composition and st ructure is similar to the mineral part of bone. As an alternative to traditional plasma sprayed coating technique, pulsed l aser deposition (PLD) has been applied due to its ability to reproduce comp lex stoichiometries. A hydroxylapatite target was ablated with an ArF laser in a water vapor atmosphere to investigate in which range of fluences the stoichiometric transfer to a titanium substrate is possible. The Ca/P ratio of the coatings was measured by energy dispersive spectroscopy (EDS), whil e their OH- and CO32- content was evaluated by Fourier transform infrared s pectroscopy (FT-IR) spectroscopy. The irradiated target surface was analyze d by scanning electron microscopy (SEM) and the ablation rate measured with a profilometer. While at higher fluences all the target material is congruently ablated and stoichiometry is transferred to the coatings, at lower fluences (< 1.2 J c m(-2)) preferential ablation of Ca and strong out-difussion of CO32- impuri ty as CO2 takes place at the target. The incongruent melting of the hydroxy lapatite target at low fluences provokes its enrichment in Ca. The higher C a concentrations arriving to the substrate, together with the higher CO2 pa rtial pressure, yields enhanced substitution of PO43- by CO32- and increasi ng of the Ca/P ratio at the coating. (C) 2000 Elsevier Science B.V. All rig hts reserved.