Synthesis And Properties Of Y₂O₃ Thin Films On Sapphire

Sapphire exhibits excellent comprehensive performance,but strong Fresnel reflection limits its application in high-precision optical apparatus and systems.Therefore,antireflection technology is an important approach to reduce Fresnel reflection and then improve the utilization of incident light,which is finally beneficial to photoelectric conversion efficiency,optical sensor sensitivity and optical system stability.Common antireflection techniques include the multilayer optical films on sapphire or the micro/nano grating structures on it.Compared with the mentioned techniques,the composite antireflective technology proposed in this thesis,which is Y₂O₃ single-layer/micro-grating structures,can further improve the optical properties and is expected to solve such problems as the muti-layer matching and complex design.This thesis firstly focused on the effects of post-annealing temperatures on Y₂O₃ films and then researched Y₂O₃ single-layer/micro-grating structures on basis of the obtained ideal annealing temperature.The main work and results were shown as following.The yttrium oxide powders synthesized using the reactive magnetron sputtering method were prepared by dissolving the substrate（aluminum foil）,and their thermal and substance changes during heating process were analyzed.Y₂O₃ powders had only one typical endothermic peak and an obvious mass decrease between 260 °C and 330 °C.The as-deposited films were plenty of physisorbed oxygen（Oδ）which began to release into lattice oxygen and O2 at the annealing temperature of 260 °C.Y₂O₃ films synthesized by the same method were further annealed at 260,350,500 and 650 °C.There are desorption of Oδ,valence change between oxygen and yttrium atoms and electron transfer processes during the annealing process.At 260³50 °C annealing,the Oδ got electron to desorb and the yttrium atoms lose electron to enhance their valence,which drove the film to stoichiometry.The cubic phase with（111）plane was dominant not only in the as-deposited Y₂O₃ films but also in the films annealed at higher temperature.Y₂O₃ films without obvious phase transformations were prepared successfully.The typical columnar structures were found in the Y₂O₃ films of as-deposition,260 and 350 °C annealing,but they gradually disappeared at annealing temperatures higher than 500 °C.The refractive index and extinction coefficient of Y₂O₃ films decreased initially before increasing to a certain value（refractive index of 1.845 at 800 nm）and then decreased again at elevated annealing temperature.Due to the desorption of Oδ,cubic phase and columnar structures,Y₂O₃ films annealed at 350 °C showed the most optimum mechanical properties（elastic modulus EIT of 280 GPa,and hardness HIT of 12 GPa）.On the other side,the optical properties of micro-grating structure sapphire（sapphire MGS）with Y₂O₃ layer were theoretically calculated by the finite-difference time-domain method.The results showed that the total transmittance and reflectance of Y₂O₃/sapphire MGS had a close relationship with the thickness of Y₂O₃ layer.The Y₂O₃/sapphire MGS,which included 300 nm Y₂O₃ layer and the hexagonally arrayed sapphire with 1.6 μm of height,2.6 μm of width,and 0.4 μm of space length,showed the total transmittance of 91.7 % and reflectance of 7.9 %.In UV-Vis-near infra,the experimental results agreed well with the calculated data and further have better optical properties because of the rough surface of Y₂O₃ layer.It illustrated that the 300 nm Y₂O₃/sapphire MGS exhibited the best increase in the total transmittance（93 %）and diffuse transmittance（88 %）in 250 ¹200 nm wavelength due to the greater graded refractive index profile than sapphire MGS.However,Y₂O₃ layer had negative effects on the optical properties in mid-infrared,the total transmittance of which decreased by 2 % with 300 nm Y₂O₃ layer.