Evidence for Ionic Liquid Gate-Induced Metallization of Vanadium Dioxide Bars over Micron Length Scales

It has recently been shown that the metal-insulator transition in vanadium dioxide epitaxial films can be suppressed and the material made metallic to low temperatures by ionic liquid gating due to migration of oxygen. The gating is only possible on certain crystal facets where volume channels along the VO₂'s rutile c-axis intersect the surface. Here, we fabricate bars with the c-axis in plane and oriented parallel to or perpendicular to the length of the bars. We show that only bars with the c-axis perpendicular to the bars, for which the volume channels are accessible from the sides of the bar, can be metallized by ionic liquid gating. Moreover, we find that bars up to at least 0.5 μm wide can be fully gated, demonstrating the possibility of the electric field induced migration of oxygen over very long distances, ∼5 times longer than previously observed.