  Metal-insulator transitions (MIT),an intriguing correlated phenomenon induced
by the subtle competition of the electrons' repulsive Coulomb interaction and
kinetic energy, is of great potential use for electronic applications due to
the dramatic change in resistivity. Here, we demonstrate a reversible control
of MIT in VO2 films via oxygen stoichiometry engineering. By facilely
depositing and dissolving a water-soluble yet oxygen-active Sr3Al2O6 capping
layer atop the VO2 at room temperature, oxygen ions can reversibly migrate
between VO2 and Sr3Al2O6, resulting in a gradual suppression and a complete
recovery of MIT in VO2. The migration of the oxygen ions is evidenced in a
combination of transport measurement, structural characterization and
first-principles calculations. This approach of chemically-induced oxygen
migration using a water-dissolvable adjacent layer could be useful for advanced
electronic and iontronic devices and studying oxygen stoichiometry effects on
the MIT.
