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

被引:19
作者
Ali, Rizwan [1 ]
Saleem, Muhammad Rizwan [1 ,2 ]
Paakkonen, Pertti [1 ]
Honkanen, Seppo [1 ]
机构
[1] Univ Eastern Finland, Inst Photon, FI-80101 Joensuu, Finland
[2] Natl Univ Sci & Technol, Ctr Adv Studies Energy CAS EN, Islamabad 44000, Pakistan
来源
NANOMATERIALS | 2015年 / 5卷 / 02期
基金
芬兰科学院;
关键词
OXIDE-FILMS; TIO2; GRATINGS; AL2O3;
D O I
10.3390/nano5020792
中图分类号
O6 [化学];
学科分类号
0703 ;
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 (R). 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) x 10(-4) degrees C-1 and (0.680 +/- 0.313) x 10(-4) degrees C-1, respectively, at a temperature T = 62 degrees C.
引用
收藏
页码:792 / 803
页数:12
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