Electron microscopy investigation of pulsed-laser deposited hydroxylapatite thin films

摘要

Hydroxylapatite layers were grown by pulsed laser deposition on a titanium nitride buffer deposited on silicon or a titanium alloy. Usually the layers are deposited in the presence of water vapours or in oxygen with partial pressures of several mbar. In this study depositions were carried out in vacuum of about 10~(-5) Torr in order to preserve the memory of the physicochemical state of the expelled material from the target under laser beam impact. This enabled us to study the morphology, the structure and the composition of deposited material by various investigation techniques (XRD, TEM, XPS, SEM). We observed that the deposition is made essentially of hydroxylapatite that have two well-known morphologies: (ⅰ) an homogeneous film made of grains of nanometric size without chemical interaction between them and which form a not very dense film; (ⅱ) particulates (droplets) which are ejected in solid, pasty or liquid state, accredited by characteristic morphologies and which have complex structures whose origins are the physicochemical transformation and decomposition of hydroxylapatite during laser beam-target interaction. The physical conditions to obtain a continuous and dense hydroxylapatite film are discussed.