Liquid Precursor-Guided Phase Engineering of Single-Crystal VO 2 Beams.

The study of VO 2 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 VO 2 still challenging. Here, stoichiometry manipulation of single-crystal VO 2 beams in liquid-assisted growth is systematically studied. Contrary to previous experience, oxygen-rich VO 2 phases are abnormally synthesized under a reduced oxygen concentration, revealing the important function of liquid V 2 O 5 precursor: It submerges VO 2 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 V 2 O 5 precursor and thus the exposure time of VO 2 to the atmosphere, various VO 2 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 VO 2 beams, enriching their deformation modes for actuation applications.