Structure evolution in reactively sputtered molybdenum oxide thin films

• Evolution of MoOx film structure studied as function of oxygen partial pressure.
• Two different regimes of MoOx thin films observed: MoO2 and MoO3 dominated.
• Structure and properties tuneable by adjusting the oxygen content within the films.

The current work investigates structure and property relations of molybdenum oxide thin films deposited by reactive dc magnetron sputtering from a molybdenum target with varying oxygen/argon gas flow ratio during deposition. With increasing oxygen partial pressure, the film growth rate decreased from 90 to 7 nm/min, whereas the oxygen content in the films increased up to 75 at.%. The dominating phases found by X-ray diffraction and Raman spectroscopy were MoO2, different polymorphs of Mo4O11, and MoO3. The optical appearance changed from metallic to yellowish transparent with increasing oxygen content in the thin film, while the electrical properties varied from electrically conductive to insulating. In general, structure and properties of the deposited molybdenum oxide thin films are tuneable by adjusting the oxygen/argon gas flow ratio during deposition, which enables the use of these films in a wide range of optical and electronic applications.