Confocal Raman Microscopy across the Metal-Insulator Transition of Single Vanadium Dioxide Nanoparticles

We present the first Raman scattering measurements on nanoparticulate vanadium dioxide (VO2), as well as the first observations of the temperature-induced phase transition in individual VO2 nanoparticles (NPs). We compare the Raman response of two VO2 NPs and a companion VO2 film undergoing their monoclinic-tetragonal-monoclinic transformations and offer qualitative explanations for the large observed differences in hysteresis width. While bulk crystals and contiguous films contain numerous nucleation sites, individual NPs likely harbor only a few, which may make it possible to correlate detectable defects (e.g., grain boundaries and dislocations) with the ease of switching phases, as quantified by the width of the thermal hysteresis.