Phase selection and texturing in molybdenum oxide films grown by reactive magnetron sputtering

Abstract

Molybdenum oxide films offer a rich variety of properties for diverse applications, but exclusive synthesis of desired phases is a major challenge. Here, we demonstrate that oxygen flow ratio fO2 = [O2]/[Ar + O2] is crucial not only for phase selection of non-layered monoclinic MoO2 and layered orthorhombic α-MoO3 but also for controlling grain size and preferred orientation. Both mica and sapphire support exclusive MoO2 formation for 0.15 ≤ fO2 ≤ 0.25 at deposition temperatures Tdep = 400 and 500 °C, while α-MoO3 forms only at Tdep = 400 °C for 0.35 ≤ fO2 ≤ 0.5. Within the fO2 windows favoring each phase, high fO2 fosters large grains with out-of-plane 0k0 texture, except for MoO2 on c-sapphire at Tdep = 500 °C, where no fO2-texture correlation is discernible. These findings provide a framework for rational synthesis of single-phase monoclinic MoO2 and orthorhombic MoO3 with control over texture and microstructure to access desired properties.