Wet‐Etching Induced Abnormal Phase Transition in Highly Strained VO2/TiO2 (001) Epitaxial Film

Abstract

The metal–insulator transition (MIT) behavior in vanadium dioxide (VO2) epitaxial film is known to be dramatically affected by interfacial stress due to lattice mismatching. For the VO2/TiO2 (001) system, there exists a considerable strain in ultra‐thin VO2 thin film, which shows a lower Tc value close to room temperature. As the VO2 epitaxial film grows thicker layer‐by‐layer along the “bottom‐up” route, the strain will be gradually relaxed and Tc will increase as well, until the MIT behavior becomes the same as that of bulk material with a Tc of about 68 °C. Whereas, in this study, we find that the VO2/TiO2 (001) film thinned by “top‐down” wet‐etching shows an abnormal variation in MIT, which accompanies the potential relaxation of film strain with thinning. It is observed that even when the strained VO2 film is etched up to several nanometers, the MIT persists, and Tc will increase up to that of bulk material, showing the trend to a stress‐free ultra‐thin VO2 film. The current findings demonstrate a facial chemical‐etching way to change interfacial strain and modulate the phase transition behavior of ultrathinVO2 films, which can also be applied to other strained oxide films.