Influence of glass contact induced changes in surface composition of Pt, PtIr and Ir protective coatings on glass adhesion

摘要

The previously overlooked influence of glass contact-induced changes in surface composition of Pt, PtIr and Ir protective coatings on glass adhesion is investigated. All coatings, deposited onto sapphire, are subjected to contact with B270 (R) glass at the molding temperature of 680 degrees C for four hours in vacuum (= 5 x 10(-4) Pa). Optical microscopy, electron microscopy and energy-dispersive X-ray spectroscopy reveal an increase in macroscopic glass adhesion which is concurrent with the increase in Pt concentration. Consistent with these macro-scale observations, X-ray photoelectron spectroscopy (XPS) indicates not only the presence of Pt-O-Si bonds but also an increased Si concentration as the Pt concentration is increased. Furthermore, as a consequence of glass contact, a local increase in Pt concentration and hence evidence for surface Pt-enrichment is obtained. Based on thermogravimetry and XPS data, the as-deposited Ir coating exhibits the presence of a surface oxide (IrO2) that dissociates at the glass molding temperature at a rate of 3.5 wt.% per hour. Hence, IrO2 appears to provide passivation and thus inhibits glass adhesion while the presence of Pt, instigates glass adhesion by Pt-O-Si bond formation.