Infrared micro-spectroscopy of strained VO$_2$ micro-crystals

The temperature-driven insulator-to-metal transition (IMT) in vanadium dioxide (VO$_2$) is accompanied by a structural instability (SI). The IMT and SI lead to a drastic change in the electronic properties, crystal structure, and lattice dynamics. We performed infrared micro-spectroscopy on single crystal platelets of VO$_2$ deposited on oxidized silicon substrate by physical vapor deposition. The firm attachment of these micro-crystals to the substrate causes strain which can alter their properties compared to bulk samples. We report infrared data on these micro-crystals and demonstrate both their electronic and phonon properties in the monoclinic M1 phase and the rutile phase. We also compare their infrared conductivity to that of bulk single crystals and thin films. Finally, we compare infrared-active phonon features to first-principles density functional theory calculations.