Enhanced performance of room-temperature-grown epitaxial thin films of vanadium dioxide

Vanadium dioxide (VO2) in bulk, thin-film, and nanostructured forms exhibits an insulator-to-metal transition accompanied by structural reorganization, induced by temperature, light, electric fields, doping, or strain. We have grown epitaxial films of VO2 on c-cut (0001) sapphire following two different procedures: (1) room-temperature growth followed by annealing and (2) direct high-temperature growth. We find that variations in strain at the film-substrate interface in the two protocols leads to differences in morphologies and transition characteristics. Our results show that room-temperature-grown epitaxial films have smoother morphologies and better switching contrast, analogous to the enhanced performance of epitaxially grown compound semiconductors.