Photoluminescence and wettability control of NiFe/ZnO heterostructure bilayer films

Abstract

The controllable photoluminescence and wettability of NiFe/ZnO heterostructure bilayer films have been demonstrated by applying an ultrathin NiFe capping layer onto ZnO films by radio-frequency magnetron sputtering at room temperature without introducing any oxygen gas during the deposition process. High quality crystalline ZnO(002) textured films were fabricated at first and displayed a remarkable near-band-edge emission peak located at around 370 nm with a bandgap of 3.35 eV confirmed by room temperature photoluminescence spectra. Once the ZnO films were capped with a single NiFe layer, ranging from 5 to 20 nm in thickness, the intensity of their near-band-edge emission peak decreased and the emission band shifted to 414 nm. On the other hand, the contact angle of the uncapped ZnO film increased from 88° to 101° with the addition of a 10 nm thick NiFe capping layer. This means that the ultrathin NiFe layer acted as a surfactant layer. The surface wettability could be switched from hydrophilic to hydrophobic due to the varied surface free energy caused by the controllable grain morphology of the NiFe/ZnO heterostructures. This work demonstrates that a direct NiFe capping layer can effectively control the optical, surface and magnetic characteristics in NiFe/ZnO heterostructures depending on the bimetallic NiFe thickness and provide valuable multifunctional behaviors for potential novel magnetoelectric applications.