Asymmetric strain in a substrate material induced by localized phase transition in a thin film

Substrates are most typically used as supporting structures that define lattice constraints for the films they support. Strain engineering, whereby the substrate is chosen to tune properties in the film, is often the focus of thin film research. Little attention is given to the reverse mechanism by which films can modify the substrate they support. Here we present evidence of a local phase transition in a thin film material, VO₂, which can compressively strain the substrate, Al₂O₃, in the region of the localized transition. This strain on the substrate also leads to feedback in the film defining an anisotropic development of this localized transition. Using a novel non-invasive full-field X-ray imaging modality for depth resolved imaging, we also show this effect can propagate deep into the substrate up to 300 times the film thickness. These results present a continuing understanding of the interactions of substrates on film properties and provide new avenues to study the causes of idiosyncratic behaviors in transition metal oxide systems. Beyond a fundamental understanding of these systems, self-induced feedback between the films and their substrates may present avenues for 3D neuromorphic computing and out-of-plane coupling for 2D materials.