Physicochemical properties of calcium phosphate coatings produced by pulsed laser deposition at different water vapour pressures

Calcium phosphate coatings were produced by pulsed laser deposition from targets of non-stoichiometric hydroxyapatite (image = 1.70) at a substrate temperature of 485°C and different proccessing pressures of water vapour: 0.15, 0.30, 0.45, 0.60 and 0.80 mbar. The physicochemical properties of these coatings were studied using Fourier-transform IR spectroscopy (FT-IR) and energy dispersive X-ray analysis (EDX). A minimum pressure of water vapour was necessary in order to obtain a crystalline coating, as deduced from the FT-IR spectroscopy of these coatings. This analysis also revealed that when the deposition pressure of water vapour was further increased, the coatings were less crystalline and the content of hydroxyl groups, the carbonate substitution for phosphate, and the image ratio, as measured by EDX, were lower. These effects can be explained by a combined substitution of carbonate and HPO2−4 for phosphate, being predominant the carbonate substitution at low pressures and the HPO2−4 substitution at high pressures.