Improved metal-insulator-transition characteristics of ultrathin VO ₂ epitaxial films by optimized surface preparation of rutile TiO ₂ substrates

Key to the growth of epitaxial, atomically thin films is the preparation of the substrates on which they are deposited. Here, we report the growth of atomically smooth, ultrathin films of VO2 (001), only ∼2 nm thick, which exhibit pronounced metal-insulator transitions, with a change in resistivity of ∼500 times, at a temperature that is close to that of films five times thicker. These films were prepared by pulsed laser deposition on single crystalline TiO2(001) substrates that were treated by dipping in acetone, HCl and HF in successive order, followed by an anneal at 700-750 C in flowing oxygen. This pretreatment removes surface contaminants, TiO 2 defects, and provides a terraced, atomically smooth surface. © 2014 AIP Publishing LLC.