Optical properties of sputter-deposited cerium oxyfluoride thin films

CeO(x)F(y) films were made by reactive rf magnetron sputtering of Ce in Ar + O(2) + CF(4). Stoichiometries between CeO(2) and CeO(1.0)F(1.3) were obtained when the CF(4) content lay between 0% and 9%. For wavelengths λ of > 0.4 µm, the films were almost nonabsorbing, and the refractive index at λ = 0.55 µm went from 2.32 for CeO(2) to 1.62 at 9% CF4(4). At λ < 0.4 µm and <4% CF(4), the optical properties were consistent with an indirect band gap at 3.1-3.2 eV. CeO(2) films could serve as intercalation hosts for Li(+) ions.