Evolution of the deposition rate during pulsed laser deposition of hydroxyapatite coatings and its relation with target morphology

The evolution of the deposition rate during pulsed laser deposition of hydr oxyapatite coatings with a KrF excimer laser was studied. This evolution wa s related to the changes produced on the target morphology during laser irr adiation. Laser fluences in the 1.0-5.2 J/cm(2) range, typical for the depo sition of hydroxyapatite coatings, were investigated. Deposition rates were measured through a quartz-crystal microbalance. and the target surface was observed by scanning electron microscopy. At the lowest fluences, the depo sition rate decreases as the number of pulses increases. At the same time, a cone structure is developed on the target surface. At the highest fluence s, the deposition rate increases with the number of pulses. In this case, t he target surface becomes rough but cones are not formed. In all cases, an enlargement of the effective irradiated area results. This enlargement prod uces the effect of fluence dilution and also an increase of the emitting ar ea. These opposite effects could account for the different evolutions found for the deposition rate. At low fluences the effect of fluence dilution wo uld predominate over the increase of the emitting area, and at high fluence s the second effect would predominate over the first.