Direct correlation of structural domain formation with the metal-insulator transition in VO$_{2 }$nanobeams

While the metal-insulator transition in VO$_{2}$ bulk and thin films has been investigated for decades, recent studies of nanobeams have provided new insights into nature of the phase transition, in particular the relationship between inhomogeneous strain and metal/insulator domain formation. We have used Raman spectroscopy mapping of single nanobeam electrical devices at varying temperatures to directly correlate the domain structure with electrical resistance. With increasing temperature, clamped nanobeams transform from the insulating monoclinic M$_{1}$ phase to a mixture of the metastable Mott-insulating M$_{2}$ phase and the metallic rutile phase. Domain fractions were used to extract the temperature dependent resistivity of the M$_{2}$ phase, which shows an activated behavior consistent with the expected Mott-Hubbard gap. A metallic monoclinic M$_{2}$ phase was also produced by direct injection of charge into the device, providing evidence of an insulator-to-metal transition without a structural phase transformation.