Film thickness variation mediated interfacial strain crossover in epitaxial VO_2 films

摘要

In this presentation, we show the correlation between the interfacial strain and the insulator-metal-transition (IMT) of VO2 films. The (020) oriented epitaxial VO_2 films were grown on Al2O3(0001) using RF-magnetron sputtering at various deposition time to obtain different interfacial strain state. As deposition time increased, the in-plane (out-of-plane) compressive (tensile) strain decreased from -1.64 % (0.23 %) to -0.21 % (-0.04 %). Furthermore, IMT temperature shifted to higher temperature with decreasing the interfacial strain. From the local structure analysis, we found that a V-V chain length was more sensitive to the interfacial strain than an apical and equatorial V-O bond length. According to the DFT calculations, the d*// orbital occupancy was shifted to the Fermi level with increasing the V-V chain length suggesting, the shift of transition temperature. In addition, the variation of d*// orbital occupancy was also experimentally confirmed by polarization-dependent X-ray absorption spectroscopy. These results provide a better understanding of the interfacial strain induced IMT mechanism.