ZnO thin films, used as polymer protection layers against ultraviolet radiation and atomic oxygen for space application, were deposited on polyimide foil substrates using a cathodic vacuum arc deposition technique. A fragmentation test was employed to investigate the influence of deposition pressure on the adhesion of ZnO thin films. It was found that all the samples have good adhesive properties. Low deposition pressure is beneficial to the adhesion of ZnO films and polyimide substrates. Scanning electron microscopy was also employed to investigate the surface morphology of ZnO films that had suffered from large strain. No large areas of film detachment were found.
The interfacial interaction between the ZnO film and the polyimide substrate was investigated by XPS and density functional theory (DFT) calculation, for the ZnO thin films deposited on polyimide (PI) substrates using cathodic vacuum arc deposition technique. The XPS results showed that a shoulder peak was present for the ZnO film with the thickness of about 15 nm, used for depth profiling, at the binding energy 1 eV higher than that of the Zn2p3 core level for bulk ZnO. Such a shoulder peak is attributed to the interaction between the ZnO and the polyimide. This agrees with the results of DFT calculation. Furthermore, the difference in adsorption energy between the polyimide monomer and the ZnO molecule at different adsorption sites showed that the carbonyl (C O) plays an important role in the interfacial strength.
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