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.
References
Calculating the film thicknesses by dividing the RBS areal density (atoms/area) by the film density (atoms/volume) calculated from the measured a-axis and c-axis lengths (Fig. 2(d)) is also consistent with the thicknesses given in Table I as the uncertainty in thickness is dominated by the uncertainty in the RBS areal density, not the film density. For this calculation, films thinner than 10 nm were assumed to be commensurate.
