Thermo-Optical Properties of Thin-Film TiO2–Al2O3 Bilayers Fabricated by Atomic Layer Deposition

Nanomaterials

Rizwan Ali¹  Muhammad Rizwan Saleem¹  Pertti Pääkkönen¹  Seppo Honkanen¹ 

[1] Institute of Photonics, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland; E-Mails:

关键词: atomic layer deposition (ALD);    thin barrier films;    thermo-optic coefficient;    titanium dioxide;    aluminum oxide;    optical materials;   

DOI  :  10.3390/nano5020792

来源: mdpi

【 摘 要 】

We investigate the optical and thermo-optical properties of amorphous TiO₂–Al₂O₃ thin-film bilayers fabricated by atomic layer deposition (ALD). Seven samples of TiO₂–Al₂O₃ bilayers are fabricated by growing Al₂O₃ films of different thicknesses on the surface of TiO₂ films of constant thickness (100 nm). Temperature-induced changes in the optical refractive indices of these thin-film bilayers are measured by a variable angle spectroscopic ellipsometer VASE®. The optical data and the thermo-optic coefficients of the films are retrieved and calculated by applying the Cauchy model and the linear fitting regression algorithm, in order to evaluate the surface porosity model of TiO₂ films. The effects of TiO₂ surface defects on the films’ thermo-optic properties are reduced and modified by depositing ultra-thin ALD-Al₂O₃ diffusion barrier layers. Increasing the ALD-Al₂O₃ thickness from 20 nm to 30 nm results in a sign change of the thermo-optic coefficient of the ALD-TiO₂. The thermo-optic coefficients of the 100 nm-thick ALD-TiO₂ film and 30 nm-thick ALD-Al₂O₃ film in a bilayer are (0.048 ± 0.134) × 10⁻⁴ °C⁻¹ and (0.680 ± 0.313) × 10⁻⁴ °C⁻¹, respectively, at a temperature T = 62 °C.

【 授权许可】

CC BY   
© 2015 by the authors; licensee MDPI, Basel, Switzerland