Liquid Precursor-Guided Phase Engineering of Single-Crystal VO₂ Beams

The study of VO₂ flourishes due to its rich competing phases induced by slight stoichiometry variations. However, the vague mechanism of stoichiometry manipulation makes the precise phase engineering of VO₂ still challenging. Here, stoichiometry manipulation of single-crystal VO₂ beams in liquid-assisted growth is systematically studied. Contrary to previous experience, oxygen-rich VO₂ phases are abnormally synthesized under a reduced oxygen concentration, revealing the important function of liquid V₂ O₅ precursor: It submerges VO₂ crystals and stabilizes their stoichiometric phase (M1) by isolating them from the reactive atmosphere, while the uncovered crystals are oxidized by the growth atmosphere. By varying the thickness of liquid V₂ O₅ precursor and thus the exposure time of VO₂ to the atmosphere, various VO₂ phases (M1, T, and M2) can be selectively stabilized. Furthermore, this liquid precursor-guided growth can be used to spatially manages multiphase structures in single VO₂ beams, enriching their deformation modes for actuation applications.