Novel TiO2/ZnO multilayer mirrors at 'water-window' wavelengths fabricated by atomic layer epitaxy

We propose that novel oxide superlattice structures of crystalline TiO₂/ZnO on sapphire substrates can be used for multilayer mirrors with high reflectivity at 2.734 nm. In the experimental study, both rutile TiO₂(200) and wurtzite ZnO(001) thin films were grown epitaxially on the same sapphire (001) substrate by atomic layer epitaxy (ALE) at 450 °C. We also demonstrated that the novel oxide superlattice structure of 10-bilayer TiO₂/ZnO on a sapphire substrate gave a high reflectivity of 29.4% at 2.74 nm.