Optical properties of LaF3 thin films prepared by thermal evaporation and ion beam sputtering
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摘要: 研究了钼舟热蒸发工艺和离子束溅射方法制备的单层LaF3薄膜的特性。首先，采用分光光度计测量了LaF3薄膜的透射率和反射率光谱，使用不同模型拟合得出薄膜的折射率和消光系数。然后，采用应力仪测量了加热和降温过程中LaF3薄膜的应力-温度曲线。最后，采用X射线衍射仪测试了薄膜的晶体结构。实验结果表明，热蒸发制备的LaF3（RH LaF3）存在折射率的不均匀性，在193 nm，其折射率和消光系数分别为1.687和510-4，而离子束溅射制备的LaF3（IBS LaF3）折射率和消光系数分别为1.714和910-4。两种薄膜表现出相反的应力状态，RH LaF3薄膜具有张应力，而IBS LaF3具有压应力，退火之后其压应力减小。热蒸发制备的MgF2/LaF3减反膜在193 nm透过率为99.4%，反射率为0.04%，离子束溅射制备的AlF3/LaF3减反膜透过率为99.2%，反射率为0.1%。Abstract: To meet the requirements for different practical applications, we investigate the properties of single LaF3 layer deposited by resistive heating Mo-boat(RH) and ion beam sputtering(IBS) in this paper. First, transmittance and reflectance spectra of LaF3 thin films were measured by an UV-visible spectrophotometer, and the refractive indexes and extinction coefficients were obtained by using different models. Second, stress-temperature curves of LaF3 thin films during heating and cooling cycles were carried out by a stress measurement system. Finally, the X-ray diffraction(XRD) was used to characterize the microstructure of LaF3 layers. Experimental results indicate that LaF3 thin film fabricated by thermal evaporation(RH LaF3) had an inhomogeneous refractive index; the refractive index and extinction coefficient at 193 nm are 1.687 and 510-4 for RH LaF3, and 1.714 and 910-4for IBS LaF3, respectively. RH LaF3 and IBS LaF3 exhibited inverse stress status. RH LaF3 had a tensile stress and IBS LaF3 showed a compressive stress, which decreased after annealing. The transmittances are 99.4% and 99.2% for RH deposited MgF2/LaF3 AR coating and IBS deposited AlF3/LaF3 AR coating, and the corresponding measured reflectances are 0.04% and 0.1%,respectively.
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Key words:
- thin films /
- LaF3 /
- thermal evaporation /
- ion beam sputtering /
- stress /
- AR
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