Fig. 1. XRD patterns of the yttrium fluoride films deposited under 150, 200, and 250 W and target

Fig. 2. XPS spectra for the surface of the yttrium fluoride films deposited under 150, 200, and 250 W

Fig. 3. Fine spectra of the Y 3d core level for the films and the fitted XPS spectra of the Y 3d core level under different powers. (a) Fine spectra of thin films; (b) fitted spectra under 150 W; (c) fitted spectra under 200 W; (d) fitted spectra under 250 W

Fig. 4. Transmittance spectra of the deposited yttrium fluoride films and germanium substrate

Fig. 5. Extinction coefficient curves of yttrium fluoride films deposited under 150, 200, and 250 W

Fig. 6. Refractive index curves of yttrium fluoride films deposited under 150, 200, and 250 W

Fig. 7. Transmittance spectra of experimental and fitted data for yttrium fluoride films deposited under different powers. (a) 150 W; (b) 200 W; (c) 250 W

Fig. 8. Surface morphologies of yttrium fluoride films deposited under different powers. (a) 150 W; (b) 200 W; (c) 250 W