Optimization of optical and structural properties of Al₂O₃/TiO₂ nano-laminates deposited by atomic layer deposition...

Optimizing the atomic layer deposition (ALD) process of films is particularly important in preparing multilayer interference films. In this work, a series of Al₂O₃/TiO₂ nano-laminates with a fixed growth cycle ratio of 1:10 were deposited on Si and fused quartz substrates at 300 °C by ALD. The optical properties, crystallization behavior, surface appearance and microstructures of those laminated layers were systematically investigated by spectroscopic ellipsometry, spectrophotometry, X-ray diffraction, atomic force microscope and transmission electron microscopy. By inserting Al₂O₃ interlayers into TiO₂ layers, the crystallization of the TiO₂ is reduced and the surface roughness becomes smaller. The TEM images show that excessively dense distribution of Al₂O₃ intercalation leads to the appearance of TiO₂ nodules, which in turn leads to increased roughness. The Al₂O₃/TiO₂ nano-laminate with a cycle ratio 40:400 has relatively small surface roughness. Additionally, oxygen-deficient defects exist at the interface of Al₂O₃ and TiO₂, leading to evident absorption. Using O₃ as an oxidant instead of H₂O for depositing Al₂O₃ interlayers was verified to be effective in reducing absorption during broadband antireflective coating experiments.