Abstract
Vanadium dioxide (VO2) exhibits a reversible insulator-metal phase transition that is of significant interest in energy-efficient nanoelectronic and nanophotonic devices. In these applications, crystalline materials are usually preferred for their superior electrical transport characteristics as well as spatial homogeneity and low surface roughness over the device area for reduced scattering. Here, we show applied electrical currents can induce a permanent reconfiguration of polycrystalline VO2 nanowires into crystalline nanowires, resulting in a dramatically reduced hysteresis across the phase transition and reduced resistivity. Low currents below 3 mA were sufficient to cause the local temperature in the VO2 to reach about 1780 K to activate the irreversible polycrystalline-to-crystalline transformation. The crystallinity was confirmed by electron microscopy and diffraction analyses. This simple yet localized post-processing of insulator-metal phase transition materials may enable new methods of studying and fabricating nanoscale structures and devices formed from these materials.
Highlights
Currents and the crystallization process can be extremely rapid
The centre of the VO2 wire reaches the highest temperature of 1780 K, similar to the value extrapolated from the one dimensional Fourier model and Interestingly, the highest temperature region is localized to the centre of the nanowire, which may explain why the contact resistance was unchanged in the polycrystalline-to-crystalline transformation as the temperature may not have been sufficiently high at the Pd contacts for VO2 to crystallize
We have demonstrated the transformation of polycrystalline VO2 into crystalline VO2 in nanowire geometries by injecting electrical currents of the order of 1 mA to reach local temperatures near 1780 K
Summary
Currents and the crystallization process can be extremely rapid. This process is in contrast to the typical thermal annealing of VO2, in which the film is heated gradually and uniformly to reduce V2O5 into VO2 or create oxygen vacancies[27,28,29]. Phase transition temperatures were about the same at approximately 343 K, but in the “after” case, the hysteresis width was reduced to about 3 K, identical to that of single crystal VO219,20,23,34.
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