Effect of Microstructure of TiO2 Thin Films on Optical Band Gap Energy

TiO2 coatings are prepared on fused silica with conventional electron beam evaporation deposition. After annealed at different temperatures for four hours, the spectra and XRD patterns of TiO2 thin film are obtained. XRD patterns reveal that only anatase phase can be observed in TiO2 coatings regardless of the different annealing temperatures, and with the increasing annealing temperature, the grain size gradually increases. The relationship between the energy gap and microstructure of anatase is determined and discussed. The quantum confinement effect is observed that with the increasing grain size of TiO2 thin film, the band gap energy shifts from 3.4 eV to3.21 eV. Moreover, other possible influence of the TiO2 thin-film microstructure, such as surface roughness and thin film absorption, on band gap energy is also expected.     

退火对ZrO2薄膜微结构及激光损伤阈值的影响

利用电子束蒸发方法在Yb∶YAG晶体和熔融石英衬底上沉积单层ZrO2薄膜,分别在673 K和1 073 K的温度下经过12 h退火以后,通过X射线衍射（XRD）分析了薄膜晶相,计算了薄膜的晶粒尺寸;利用表面热透镜技术获得了薄膜的吸收;测量了退火后薄膜的激光损伤阈值。实验结果表明:两种衬底上的薄膜结构受到退火温度和衬底表面结构的影响,高温退火有利于单斜相的形成,含单斜相的ZrO2薄膜具有较高的激光损伤阈值,而由于衬底的吸收,Yb∶YAG晶体上薄膜的损伤阈值远小于石英衬底上薄膜的损伤阈值。     

Influence of Annealing Temperature on Structure, Optical Loss and Laser-Induced Damage Threshold of TiO2 Thin Films

TiO2 thin films are prepared on fused silica with conventional electron beam evaporation deposition. After annealed at different temperatures for 4h, the spectra and XRD patterns of the TiO2 thin film are obtained. Weak absorption of coatings is measured by the surface thermal lensing technique, and laser-induced damage threshold （LIDT） is determined. It is found that with the increasing annealing temperature, the transmittance of TiO2 films decreases. Especially when coatings are annealed at high temperature over 1173K, the optical loss is very serious. Weak absorption detection indicates that the absorption of coatings decreases firstly and then increases, and the absorption and defects play major roles in the LIDT of TiO2 thin films.