Controlling Metal-Insulator Transitions in Vanadium Oxide Thin Films by Modifying Oxygen Stoichiometry

TL;DR

This paper introduces a high-vacuum gas evolution technique to precisely control oxygen stoichiometry in vanadium oxide thin films, enabling tunable metal-insulator transitions and phase stability for advanced material applications.

Contribution

The study presents a novel method for controlling oxygen content in VOX thin films, allowing phase manipulation and insight into thin film phase stability differing from bulk materials.

Findings

Controlled phase transitions between VO2, V3O5, and V2O3 achieved.

Optimal stoichiometry stabilizes pronounced metal-insulator transitions.

Thin film phase diagram differs from bulk due to strain effects.

Abstract

Vanadium oxides are strongly correlated materials which display metal-insulator transitions as well as various structural and magnetic properties that depend heavily on oxygen stoichiometry. Therefore, it is crucial to precisely control oxygen stoichiometry in these materials, especially in thin films. This work demonstrates a high-vacuum gas evolution technique which allows for the modification of oxygen concentration in VOX thin films by carefully tuning thermodynamic conditions. We were able to control the evolution between VO2, V3O5, and V2O3 phases on sapphire substrates, overcoming the narrow phase stability of adjacent Magn\'eli phases. A variety of annealing routes were found to achieve the desired phases and eventually to control the metal-insulator transition (MIT). The pronounced MIT of the transformed films along with the detailed structural investigations based on x-ray diffraction measurements and reciprocal space mapping show that optimal stoichiometry is obtained and stabilized. Using this technique, we find that the thin film V-O phase diagram differs from that of the bulk material due to strain and finite size effects. Our study demonstrates new pathways to strategically tune the oxygen stoichiometry in complex oxides and provides a roadmap for understanding the phase stability of VOX thin films.