Twin-domain epitaxial growth and metal-insulator transition of VO ₂ thin film on C-plane sapphire

We report heteroepitaxial growth of VO₂ thin film on c-plane sapphire by pulsed DC magnetron sputtering. X-ray diffraction experiment indicates that the 150 nm thick film is in triple-domain (020)-epitaxial structure with six-fold rotational symmetry in the basal plane; in particular, off-axis Φ scans from (011) and (220) show twin and triple peaks in each group of the diffraction profiles due to angle β mismatch and V ⁴⁺-V⁴⁺ dimerization, respectively. The epitaxial relationship between VO₂ and c-plane sapphire can be concluded as be VO₂ [010] || Al₂O₃ [0001] and VO₂ (202) || Al₂O₃ {1120}, with the in-plane lattice mismatch of 2.66% (tensile) along [202] and the out-of-plane lattice mismatch of-2.19% (compressive). Temperature dependence of resistivity in van der Pauw method shows that the resistivity changes by ∼5 orders of magnitude through the metal-insulator transition, and a narrow hysteresis window of ∼3 K is obtained between cooling and heating cycles with respect to phase-transition temperatures at 347.1 and 350.1 K.