In situ nanomechanical behaviour of coexisting insulating and metallic domains in VO2 microbeams

Measuring the electrical and mechanical responses of coexisting phases at nanoscale provides a platform to engineer micro-/nanoscale pattern of metallic and insulating domains with control over properties to make novel devices. Here, we employ several in situ characterization techniques, namely Raman, optical imaging and electrical measurements, to identify the phase coexistence of metallic and insulating domains. Further, we performed site-specific in situ nanoindentation to address the spatial variation in nanomechanical properties in vanadium dioxide (VO2) single-crystal microbeams in proximity to metal-insulator transition temperature. We also investigated load or contact depth dependence on elastic modulus at various temperatures to avoid the interference of indentation size effect on nanomechanical properties across the phase transition. The obtained results confirm the abrupt increase in elastic modulus (similar to 17 GPa) and nanohardness (1 GPa) across the transition from monoclinic (insulator) to rutile (metal) phase.