Pulse repetition rate dependence of hydroxylapatite deposition by laser ablation

Hydroxylapatite (HA) is used as coating on metallic dental and orthopaedical implants due to its similarity to the mineral part of bone. As an alternative to the commercial plasma spraying coating technique, pulsed laser deposition has been applied. In order to study the possibility of obtaining high-deposition rates by varying the pulse repetition rate, a HA target was ablated with an ArF laser at an energy density of 0.9 J cm(-2) in a water vapour pressure of 45 Pa, and the material was deposited on a titanium substrate held at 460degreesC. The coating thickness was measured by profilometry. The phases present in the coating were detected by X-ray diffraction. Their Ca/P ratios were determined by energy dispersive X-ray spectrometer, while their OH- and CO32- contents were evaluated by Fourier transform infrared. As the pulse repetition rate is increased from 20 to 80 Hz, the structural order of the coatings decreases, and, eventually, at 100 Hz the coatings become amorphous. When the time interval between pulses is too short there is not enough time for the material to diffuse within the surface and accommodate in the structure before the material from the next pulse arrives. A long time between pulses also promotes the desorption of species from the substrate surface, preferentially CO32-. (C) 2002 Elsevier Science Ltd. All rights reserved.