Microstructure and optical properties of Al2O3/ZrO2 nano multilayer thin films prepared by pulsed laser deposition

The aluminium oxide/zirconium oxide (Al₂O₃/ZrO₂) nanolaminate thin films (5/20 nm with 4 bilayers, 5/15 nm with 5 bilayers and 5/10 nm with 7 bilayers) were deposited on Si (100) and quartz substrates at an optimized oxygen partial pressure of 3 × 10⁻² mbar at room temperature using pulsed laser deposition. The multilayer films were characterized using X-ray diffraction, X-ray reflectivity, Atomic force microscopy and UV–Visible spectroscopy. The X-ray diffraction studies showed amorphous nature for 5/20 nm film, whereas 5/15 nm and 5/10 nm multilayers showed only tetragonal zirconia at room temperature. X-ray reflectivity studies showed the Kiessig fringes and Bragg peaks, indicating the well defined formation of individual layers and bilayer periodicity in the multilayer films. The AFM studies showed the RMS roughness values of 0.7 nm, 0.9 nm and 1.1 nm for 5/10 nm, 5/15 nm and 5/20 nm multilayers respectively. The optical performance of the combined Al₂O₃/ZrO₂ nanolaminates showed that the refractive indices of the films increased from 1.75 to 1.99 with the decrease of ZrO₂ layer thickness from 20 to 10 nm.