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

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 degrees 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.(c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

In this study, a series of Al2O3/TiO2 nano-laminates were prepared by atomic layer deposition (ALD) on Si and fused quartz substrates, and their optical properties, crystallization behavior, surface appearance and microstructures were investigated. By inserting Al2O3 interlayers into TiO2 layers, the crystallization of TiO2 was reduced and the surface roughness decreased. Excessively dense distribution of Al2O3 intercalation resulted in the appearance of TiO2 nodules and increased surface roughness. The Al2O3/TiO2 nano-laminate with a cycle ratio of 40:400 had relatively small surface roughness. Additionally, oxygen-deficient defects at the Al2O3 and TiO2 interface caused significant absorption. Using O3 instead of H2O as an oxidant for Al2O3 interlayers effectively reduced absorption during broadband antireflective coating experiments.