Resonant Frequency Behavior of Silicon Cantilevers Coated With Nanostructured and Microcrystalline VO $_2$ Films

This letter reports the resonant frequency shifts of single crystal silicon cantilevers coated with vanadium dioxide (VO₂) thin films with different average crystallite sizes during the coating´s insulator-to-metal transition (IMT) and the Young´s modulus of such thin films as a function of temperature for their monoclinic phase. The IMT was induced by sample heating, and resonant frequency shifts, close to 4% of their room temperature value, were observed for the coated cantilevers with crystallite sizes in the order of ~100 nm. The resonant frequency shifts and the hysteresis curve steepness were found to be decreased for samples with smaller VO₂ film crystallite sizes and similar compositions. The crystallite sizes were controlled by the in situ annealing time to which the samples were subjected after their deposition at room temperature by pulsed laser deposition. The Young´s modulus for VO₂ samples along the monoclinic (011) plane was found to be linearly dependent on the temperature. A sigmoid curve fit was used to model the behavior of the resonant frequency of the coated cantilevers during the IMT. The results presented show that the VO₂ thin films can be useful in novel microscale and nanoscale electromechanical resonators in which the resonant frequency can be tuned electrically, thermally, or optically.