Compositional correlation and polymorphism in BaF2-PrF3 thin films deposited using electron-beam evaporation

摘要： Infrared low-index evaporation materials are essential in the broadband antire?ection coatings to reduce Fresnel re?ections on the surfaces of infrared optical components. Although the layers of praseodymium ?uoride (PrF3) show an excellent transparency and the lower refractive index n and extinction coe?cient k in the spectral range of thermal infrared, the tensile stress presented in the layers prohibits PrF3 from being used as infrared low-index coating materials. A practical solution to reduce stress is to directly evaporate the admixture of PrF3 with alkaline ?uorides, such as barium ?uoride (BaF2). However, due to the signi?cant di?erence of vapor pressures between PrF3 and BaF2, it is commonly di?cult to congruently deposit PrF3-BaF2 thin ?lms utilizing evaporating directly from a single source. Moreover, more details are unknown about the phase compositions of PrF3-BaF2 thin ?lms. In our investigation, BaF2-PrF3 thin ?lms were deposited using electron beam evaporation from the sintered ingots of PrF3 admixed with BaF2. The compositions of thin ?lms were characterized using energy dispersive X-ray spectroscopy (EDX), the crystallographic structures were explored by X-ray-di?raction (XRD). It was revealed that the concentration of BaF2 in thin ?lms can be correlated to that in the admixtures. Moreover, in addition to PrF3 and BaF2, the phase compositions in thin ?lms include also secondary phases, such as PrOF, PrF4, Pr2F2, BaPrF6, and that of elemental Ba.