Calcium phosphate thin film processing by pulsed laser deposition and in situ assisted ultraviolet...

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JOURNAL OF MATERIALS SCIENCE: MATERIALS IN MEDICINE 13 (2002) 1167±1173 Calcium phosphate thin ®lm processing by pulsed laser deposition and in situ assisted ultraviolet pulsed laser deposition V. NELEA*, H. PELLETIER Laboratoire d'Inge Ânierie de Surface, Ecole Nationale Supe Ârieure des Arts et Industries, 24 Bld. de la Victoire, F-67084, Strasbourg, France M. ILIESCU, J. WERCKMANN Groupe Surfaces Interfaces, Institut de Physique et Chimie des Mate Âriaux, 23, Rue de Lúss, F-67037, Strasbourg, France V. CRACIUN Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, USA I. N. MIHAILESCU, C. RISTOSCU Laser Department, National Institute for Lasers, Plasma and Radiation Physics, PO Box MG-36, RO-76900, Bucharest, Magurele, Romania C. GHICA National Institute of Materials Physics, PO Box MG-7, RO-76900, Bucharest, Magurele, Romania E-mail: [email protected]; nelea@i®n.nipne.ro Calcium orthophosphates (CaP) and hydroxyapatite (HA) were intensively studied in order to design and develop a new generation of bioactive and osteoconductive bone prostheses. The main drawback now in the CaP and HA thin ®lms processing persists in their poor mechanical characteristics, namely hardness, tensile and cohesive strength, and adherence to the metallic substrate. We report here a critical comparison between the microstructure and mechanical properties of HA and CaP thin ®lms grown by two methods. The ®lms were grown by KrF* pulsed laser deposition (PLD) or KrF* pulsed laser deposition assisted by in situ ultraviolet radiation emitted by a low pressure Hg lamp (UV-assisted PLD). The PLD ®lms were deposited at room temperature, in vacuum on Ti±5Al±2.5Fe alloy substrate previously coated with a TiN buffer layer. After deposition the ®lms were annealed in ambient air at 500± 600 C. The UV-assisted PLD ®lms were grown in (10 2 ±10 1 Pa) oxygen directly on Ti±5Al± 2.5Fe substrates heated at 500±600 C. The ®lms grown by classical PLD are crystalline and stoichiometric. The ®lms grown by UV-assisted PLD were crystalline and exhibit the best mechanical characteristics with values of hardness and Young modulus of 6±7 and 150± 170GPa, respectively, which are unusually high for the calcium phosphate ceramics. To the difference of PLD ®lms, in the case of UV-assisted PLD, the GIXRD spectra show the decomposition of HA in Ca 2 P 2 O 7 , Ca 2 P 2 O 9 and CaO. The UV lamp radiation enhanced the gas reactivity and atoms mobility during processing, increasing the tensile strength of the ®lm, while the HA structure was destroyed. # 2002 Kluwer Academic Publishers 1. Introduction The research in the biocompatible materials ®eld was recently strongly targeted to create coatings or thin ®lms of calcium phosphates (CaP) on mechanically resistant support [1]. The purpose of these efforts was to improve the biocompatibility of the titanium and its alloys used in bone implantology. Due to the very complex structure of bone as an organic±inorganic composite (at micro- and also at macrolevel) a material with function of arti®cial bone * Author to whom all correspondence should be addressed. On leave from National Institute for Lasers, Plasma and Radiation Physics, Lasers Department, P.O. Box MG-36, RO-76900, Bucharest, Magurele, Romania. 0957±4530 # 2002 Kluwer Academic Publishers 1167

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