Elaboration and adhesion of zinc oxide coatings on poly-ether-ether-ketone films

Zinc oxide coatings are deposited by r.f. magnetron sputtering from a ZnO target. A systematic study has been made on the influence of the sputtering parameters (oxygen partial pressure, total pressure, and r.f. power) both on the structure and on the chemical composition of the zinc oxide deposits. These thin films exhibit the zincite form with a preferred orientation along the [002] axis. The grain size becomes important once the ejected atoms reach high energies. The zinc oxide deposits have a microstructure, which varies from a large columnar structure to a more regular one depending on the process parameters. The density decreases with increasing total pressure and decreasing r.f. power during sputtering. Their composition (O/Zn atomic ratio), established by RBS, depends on the sputtering conditions. An oxygen excess is observed at low pressures. The 180° peeling test is used to evaluate the adhesion between ZnO deposits and PEEK films. This adhesion is indeed very high. This can be explained by the rupture that takes place in the ceramic rather than in the interface between the two materials as shown by X-ray energy dispersion spectrometry measurements. The surface free energies of virgin- and plasma-treated PEEK (polar and dispersive components) are determined by one and two liquid methods. The plasma treatments are found to change the polar component. The highest values are obtained with an argon–oxygen plasma mixture. XPS analyses are performed to observe the modification induced by plasma treatment of the PEEK surface and to investigate the ZnO/PEEK interface for a better understanding of the coating adhesion mechanisms of PEEK film. The improvement of the adhesion of zinc oxide coatings induced by plasma treatments is characterised by fragmentation tests.