Nd:YAG (532 nm) pulsed laser deposition produces crystalline hydroxyapatite thin coatings at room temperature

Nd:YAG (532nm) pulsed laser deposition (PLD) has been used to produce crystalline hydroxyapatite (HAP) coatings at room temperature onto silicon substrates. The PLD HAP coatings were homogeneous (100.4nm RMS roughness) and consisted of micrometric particles (>10μm) coalesced over a nanometric dense layer. The deposition parameters of 532nm laser, 30J/cm2 fluence, 10−4Pa vacuum environment and room temperature are capable of coating any surface with crystalline HAP without requiring heat treatment. It was confirmed by Synchrotron Radiation Grazing Angle X-ray Diffraction (GAXRD) patterns that the nanocrystalline component present in the coatings was reduced and did not hide peaks of decomposition to other calcium phosphate (CaP) phases when in situ heat treatments of 200°C and 800°C were performed. The use of dense and stoichiometric HAP targets that could withstand the high-fluence laser allowed producing 150nm crystalline HAP coatings in only 5min of deposition time, although 532nm laser wavelength is outside the absorption range of the HAP. This contribution opens the perspective to produce controlled PLD HAP coating over thermally sensitive substrates with reduced processing time for large-scale production for biomedical applications. As a demonstration, HAP coating was deposited and characterized on thermal sensitive bioabsorbable polylactide (PLA) surfaces.