Strong Substrate Influence on Atomic Structure and Properties of Epitaxial VO₂ Thin Films

Abstract

The metal–insulator transition (MIT) observed in vanadium dioxide has been a topic of great research interest for past decades, with the underlying physics yet not fully understood due to the complex electron interactions and structures involved. The ability to understand and tune the MIT behavior is of vital importance from the perspective of both underlying fundamental science as well as potential applications. In this work, scanning transmission electron microscopy (STEM) is used to investigate cross‐section lamella of the VO2 films deposited using pulsed laser deposition on three substrates: c‐cut sapphire, TiO2(101) and TiO2(001). Advanced STEM imaging is performed in which also the oxygen atom columns are resolved. The overall film quality and structures on atomic and nanoscale are linked to the electrical transition characteristics. Relatively poor MIT characteristics are observed on c‐sapphire due to the presence of very small domains with six orientation variants, and on TiO2 (001) due to the presence of cracks induced by stress relaxation. However, the MIT on TiO2 (101) behaves favorably, despite similar stress relaxation which, however, only leads to domain boundaries but no cracks.

Atomically Resolved Phase Coexistence in VO2 Thin Films

“…The basis of our work is the successful growth of high-quality VO 2 thin films on TiO 2 (001) substrates using pulsed laser deposition (PLD) (Figure S1), schematically shown in Figure A. Only for this substrate and specific surface orientation, the VO 2 atomic structure can be unambiguously resolved in projected images, for which we also provide more background information in another paper . We start here by schematically revealing the different structures in the specifically chosen crystallographic projections that play a key role in our approach to properly resolve all of the atomic structure details in our VO 2 films.…”