Direct correlation of structural and electrical properties of electron-doped individual VO₂ nanowires on devised TEM...

Nano-scale VO₂ wires with controlled parameters such as electron-doping have attracted intense interest due to their capability of suppressing the temperature of the metal-insulator transition (MIT). However, because their diameters are smaller than the spatial resolutions of the conventional measuring equipment, the ability to perform a thorough examination of the wires has been hindered. Here, we report the fabrication of a transmission electron microscopy (TEM) grid with an optimum design of Si₃N₄ windows on which the photolithography for individual electron-doped VO₂ nanowire devices can be safely accomplished, allowing the cross-examination of the structural and electrical properties. TEM dark-field imaging was used to quantitatively investigate the fractions of rutile and M1 phases, and their lattice alignments were observed using high-resolution TEM (HRTEM) with small area diffraction. Moreover, electron energy loss spectroscopy (EELS) revealed that the rutile domain would be created by the strain induced by oxygen vacancies. Importantly, we successfully tuned the transition temperature by changing the rutile fraction while maintaining a high level of resistivity change. The resistivity at room temperature linearly decreased with the rutile fraction, following a simple model. Furthermore, the T dependence of the threshold voltage can be attributed to the Joule heating, exhibiting an identical thermal dependence, irrespective of the rutile fraction.