Effects of oxygen in ion-beam sputter deposition of titanium oxides

Oxides of titanium, 200–400 nm thick, were deposited by ion-beam sputtering of a metallic target. The ion beam consisted of an argon–oxygen mixture where the oxygen percentage was varied from 5% to 50%. Ellipsometry and spectrophotometry were used for optical characterization, x-ray photoelectron spectroscopy to examine the atomic bonding patterns. For each wavelength, the refractive index showed a maximum when the oxygen fraction was near 30%. At 633 nm, the maximum was 2.52. Such films were dense, amorphous, stoichiometric TiO2 with a visible optical absorption of a few tenths of a percent. With less oxygen, films were also transparent, but contained increasing amounts of a titanium suboxide. With substantially less oxygen, opaque cermets were formed. When the oxygen percentage was increased above 40%, the refractive index of the films was less than the maximum, the films apparently contained voids, but they were otherwise stoichiometric.