Optical properties of sputter-deposited cerium oxyfluoride thin films

Area of Science:

• Materials Science
• Thin Film Deposition
• Optical Properties

Background:

• Cerium oxide (CeO2) is a widely studied material with diverse applications.
• Tuning the properties of cerium oxide films is crucial for advanced applications.
• Fluorination offers a pathway to modify the optical and electronic characteristics of cerium oxide.

Purpose of the Study:

• To synthesize and characterize cerium oxyfluoride (CeO(x)F(y)) thin films.
• To investigate the impact of fluorine incorporation on the optical properties of CeO(x)F(y) films.
• To explore the potential of CeO(x)F(y) films as intercalation hosts for Li(+) ions.

Main Methods:

• Reactive radio frequency (rf) magnetron sputtering of cerium (Ce) in an Ar + O2 + CF4 atmosphere.
• Controlled variation of CF4 content during sputtering to achieve different stoichiometries.
• Optical characterization including refractive index measurements and band gap determination.
• Evaluation of film properties for Li(+) ion intercalation.

Main Results:

• CeO(x)F(y) films with stoichiometries ranging from CeO2 to CeO(1.0)F(1.3) were successfully synthesized.
• Films exhibited tunable optical properties, with refractive index decreasing from 2.32 (CeO2) to 1.62 with increasing CF4 content.
• Non-absorbing behavior for wavelengths > 0.4 µm was observed.
• An indirect band gap of 3.1-3.2 eV was determined for films with <4% CF4 and λ < 0.4 µm.
• CeO2 films demonstrated potential as intercalation hosts for Li(+) ions.

Conclusions:

• Reactive sputtering enables the controlled synthesis of CeO(x)F(y) films with tunable optical properties.
• Fluorine incorporation significantly modifies the refractive index and band gap of cerium oxide films.
• CeO2 films show promise for applications requiring Li(+) ion intercalation, such as in batteries.