Transport properties of ultra-thin VO2 films on (001) TiO2 grown by reactive molecular-beam epitaxy.

We report the growth of (001)-oriented VO₂ films as thin as 1.5 nm with abrupt and reproducible metal-insulator transitions (MIT) without a capping layer. Limitations to the growth of thinner films with sharp MITs are discussed, including the Volmer-Weber type growth mode due to the high energy of the (001) VO₂ surface. Another key limitation is interdiffusion with the (001) TiO₂ substrate, which we quantify using low angle annular dark field scanning transmission electron microscopy in conjunction with electron energy loss spectroscopy. We find that controlling island coalescence on the (001) surface and minimization of cation interdiffusion by using a low growth temperature followed by a brief anneal at higher temperature are crucial for realizing ultrathin VO₂ films with abrupt MIT behavior. [ABSTRACT FROM AUTHOR]