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

TL;DR

This study demonstrates how oxygen flow ratio during reactive magnetron sputtering influences phase selection, grain size, and texture in molybdenum oxide films, enabling targeted synthesis of specific phases with controlled microstructure.

Contribution

It reveals the critical role of oxygen flow ratio in controlling phase, grain size, and orientation in molybdenum oxide films, providing a framework for tailored synthesis.

Findings

Oxygen flow ratio determines phase selection between MoO2 and MoO3.

High fO2 promotes large grains with specific texture.

Exclusive phase formation occurs within defined fO2 windows.

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 alpha-MoO3 but also for controlling grain size and preferred orientation. Both mica and sapphire support exclusive MoO2 formation in the 0.15 < fO2 < 0.25 window at deposition temperatures Tdep = 400 and 500 degree C and alpha-MoO3 formation in the 0.35 < fO2 < 0.5 window at 400 degree C. Within fO2 windows favoring exclusive phase formation, high fO2 fosters large grains with out-of-plane 0k0 texture, except for MoO2 films on c-sapphire that show no systematic trends. These findings provide a framework for rational synthesis of phase-pure monoclinic MoO2 and orthorhombic MoO3 with control over texture and microstructure to access desired properties.