The epitaxial growth and interfacial strain study of VO2/MgF2 (001) films by synchrotron based grazing incidence X-ray diffraction

High quality VO2 films with different thickness were epitaxially grown on MgF2 (001) substrates by oxide molecular beam epitaxy method. The evolution of interfacial strain was investigated by synchrotron based grazing incidence X-ray diffraction. By adjusting the incidence angles, the penetration depth of X-ray in VO2 film could be controlled and the thickness-depend lattice distortion in the epitaxial VO2 film was investigated. Due to the lattice mismatching, the pronounced tensile strain was observed in ultra-thin VO2 film. As the film thickness increasing, the interfacial strain relaxed gradually and became fully relaxed for thick VO2 films. Combined with the electric transport measurement, it was revealed that the phase transition temperature of ultra-thin VO2 film decreased greatly. The effect of interfacial strain induced phase transition modulation and the intrinsic mechanism was systematically discussed.