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 reproduciblemetal-insulator transitions (MIT) without a capping layer. Limitations to the growth of thinnerfilms with sharp MITs are discussed, including the Volmer-Weber type growth mode due to thehigh energy of the (001) VO2 surface. Another key limitation is interdiffusion with the (001) TiO2substrate, which we quantify using low angle annular dark field scanning transmission electronmicroscopy in conjunction with electron energy loss spectroscopy. We find that controlling islandcoalescence on the (001) surface and minimization of cation interdiffusion by using a low growthtemperature followed by a brief anneal at higher temperature are crucial for realizing ultrathin VO2films with abrupt MIT behavior. VC 2015 AIP Publishing LLC