Morphological anisotropy and mosaicity in epitaxially grown VO2 films

Epitaxially grown films of VO₂ are one of the most promising materials for oxide electronics due to a very convenient temperature and remarkable controllability of the insulator-to-metal phase transition (IMT) by doping, strain, photo excitations or applying an electric field. Scaling the IMT-based devices down to submicron size is a technological challenge because of the high variability of the resulted functional characteristics from device to device. Our work focuses on the structural and morphological origins of such variations. We used X-ray nano diffraction mapping to study the evolution of mosaicity, strain and phase coexistence in 70 nm thick VO₂ film (r-cut Al2O₃) during thermal cycling and annealing. We found high anisotropy in the grain and crack network structure which remarkably resonates with anisotropy of transport properties. We were able to distinguish a persistent morphological pattern due to the film manufacturing from transient features introduced by thermal cycling. Our results manifest the important role of nanomorphology in the performance of VO₂-based nanodevices. We suggest that it can also be considered as a new degree of freedom to control functional properties in oxide electronics.

This work was supported by DOE- Office of Basic Energy Sciences.