Digital Tuning of the Transition Temperature of Epitaxial VO2 Thin Films on MgF2 Substrates by Strain Engineering

Straining the vanadium dimers along the rutile c-axis can be used to tune the metal-to-insulator transition (MIT) of VO2 but has thus far been limited to TiO2 substrates. In this work VO2/MgF2 epitaxial films are grown via molecular beam epitaxy (MBE) to strain engineer the transition temperature (T-MIT). First, growth parameters are optimized by varying the synthesis temperature of the MgF2 (001) substrate (T-S) using a combination of X-ray diffraction techniques, temperature dependent transport, and soft X-ray photoelectron spectroscopy. It is determined that T-S values greater than 350 degrees C induce Mg and F interdiffusion and ultimately the relaxation of the VO2 layer. Using the optimized growth temperature, VO2/MgF2 (101) and (110) films are then synthesized. The three film orientations display MITs with transition temperatures in the range of 15-60 degrees C through precise strain engineering.

Automated summary

This study successfully demonstrated the tuning of the metal-to-insulator transition (MIT) temperature of VO2 using MgF2 substrates and epitaxial films. By optimizing growth parameters, different orientations of VO2/MgF2 films were synthesized with transition temperatures controlled precisely through strain engineering.