T$_{c}$ anisotropy and phase separation in strained Vanadium Dioxide films

We report Infrared near field study on strain induced transition temperature (T$_{c})$ anisotropy in vanadium dioxide (VO$_{2})$ films via direct visualization of a spontaneous structural and electronic phase separation. The films are epitaxially grown on [110]$_{R}$ or [100]$_{R}$ TiO$_{2}$ substrates and exhibit large uniaxial strain. By mapping the film topography with AFM and electronic percolation with Infrared scattering scanning near-field optical microscopy, a temperature dependent electron-lattice correlation can be clearly observed. Our work sheds a new light onto the nature of the Tc anomaly in metal-insulator transition and leads to the possibility of controlling the material's properties through strain induced phase separation.