Preparation of Apatite Thin Films through rf‐Sputtering from Calcium Phosphate Glasses

Abstract

Apatite thin films of calcium phosphate were successfully prepared by rf‐magnetron sputtering, followed by postannealing, from calcium phosphate glass targets with Ca/P atomic ratios of 0.6 to 0.75, much lower than the stoichio‐metric value of 1.67 for hydroxyapatite. Using targets with low Ca/P ratios of 0.65 to 0.25, tricalcium and pyrocalcium phosphate thin films were obtained. The formation of these calcium phosphates phases was attributed to the phosphorus oxide losses during sputtering. H2O vapor was effective in the formation of the apatite phase at high temperatures; apatite was the exclusive phase in the ambient H2O, even when the target with the low Ca/P ratio of 0.4 was used. Based on phase stability at high temperatures, it was assumed that various kinds of apatites, such as stoichiometric and nonstoichiometric hydroxy‐ and Ca‐deficient hydroxy‐apatites were formed, depending on the composition of the glass targets.