Reversible Entropy-Driven Defect Migration and Insulator-Metal Transition Suppression in VO 2 Nanostructures for Phase-Change Electronic Switching.

Oxygen defects are among essential issues and required to be manipulated in correlated electronic oxides with insulator-metal transition (IMT). Besides, surface and interface control are necessary but challenging in field-induced electronic switching towards advanced IMT-triggered transistors and optical modulators. Herein, we demonstrated reversible entropy-driven oxygen defect migrations and reversible IMT suppression in vanadium dioxide (VO 2 ) phase-change electronic switching. The initial IMT was suppressed with oxygen defects, which is caused by the entropy change during reversed surface oxygen ionosorption on the VO 2 nanostructures. This IMT suppression is reversible and reverts when the adsorbed oxygen extracts electrons from the surface and heals defects again. The reversible IMT suppression observed in the VO 2 nanobeam with M2 phase is accompanied by large variations in the IMT temperature. We also achieved irreversible and stable IMT by exploiting an Al 2 O 3 partition layer prepared by atomic layer deposition (ALD) to disrupt the entropy-driven defect migration. We expected that such reversible modulations would be helpful for understanding the origin of surface-driven IMT in correlated vanadium oxides, and constructing functional phase-change electronic and optical devices.