Optical and Mechanical Properties and Microstructures of Nb2O5, Ta2O5 and SiO2 Thin Films Prepared by Ion Beam Sputtering
Yuan Wenjia, Shen Weidong, Zheng Xiaowen, Yang Chenying, Zhang Yueguang, Fang Bo, Mu Wen, Chen Chaonan, Liu Xu
State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, China
Abstract
The optical and mechanical properties and the microstructures of Nb2O5, Ta2O5 and SiO2 thin films prepared by the ion beam sputtering (IBS) method are studied. The effect of the assisted ion source voltage on the film properties is analyzed. The comparison among films prepared by the electron beam evaporation, ion beam assisted deposition and IBS is also conducted. The study results show that the films prepared by IBS possess better optical performance and microstructures, as well as higher compressive stress, hardness and Young modulus. The assisted ion source is beneficial to improving the optical performance, adjusting the film stress and reducing the surface roughness of thin films, however, it has relatively small influence on the hardness and the Young modulus. Under different assisted ion source voltages, the stress of prepared Nb2O5 by IBS is -152--281 MPa, that of Ta2O5 is -299--373 MPa and that of SiO2 is -427--577 MPa. Under proper process parameters, the extinction coefficient can be smaller than 10-4 and the film surface is smooth with a root mean square roughness of smaller than 0.2 nm.
图3波长为550 nm时, 以EBE、IBAD和IBS三种方式制备的不同薄膜的光学常数。(a) Nb2O5; (b) Ta2O5; (c) SiO2Fig. 3 Optical constants of different thin films prepared by different methods of EBE, IBAD and IBS when wavelength is 550 nm.(a) Nb2O5; (b) Ta2O5; (c) SiO2
图4以EBE、IBAD和IBS三种沉积方式制备的不同薄膜的应力值。(a) Nb2O5; (b) Ta2O5; (c) SiO2Fig. 4 Stress value of different thin films prepared by three deposition methods of EBE, IBAD and IBS.(a) Nb2O5; (b) Ta2O5; (c) SiO2
图5以EBE、IBAD和IBS三种沉积方式制备的不同薄膜的硬度。(a) Nb2O5; (b) Ta2O5; (c) SiO2Fig. 5 Hardness of different thin films prepared by three deposition methods of EBE, IBAD and IBS.(a) Nb2O5; (b) Ta2O5; (c) SiO2
图6以EBE、IBAD和IBS三种沉积方式制备的不同薄膜的杨氏模量。(a) Nb2O5; (b) Ta2O5; (c) SiO2Fig. 6 Young modulus of different thin films prepared by three deposition methods of EBE, IBAD and IBS.(a) Nb2O5; (b) Ta2O5; (c) SiO2
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Good performance of optical coatings depends on the appropriate combination of optical and mechanical properties. Therefore, successful applications require good understanding of the relationship between optical microstructural and mechanical characteristics and film stability. In addition, there is a lack of standard mechanical tests that allow one to compare film properties measured in different laboratories. We give an overview of the methodology of mechanical measurements suitable for optical coatings; this includes depth-sensing indentation, scratch resistance, friction, abrasion and wear testing, and stress and adhesion evaluation. We used the techniques mentioned above in the same laboratory to systematically compare the mechanical behavior of frequently used high- and low-index materials, namely, TiO2, Ta2O5, and SiO2, prepared by different complementary techniques. They include ion-beam-assisted deposition by electron-beam evaporation, magnetron sputtering, dual-ion-beam sputtering, plasma-enhanced chemical-vapor deposition, and filtered cathodic arc deposition. The mechanical properties are correlated with the film microstructure that is inherently related to energetic conditions during film growth.
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