Local probing of electrochemically induced negative differential resistance in TiO2 memristive materials

The early stages of electroforming in TiO2 were explored using a combination of electrochemical strain microscopy and local I–V curve measurements. Negative differential resistance and corresponding surface deformation were observed below the electroforming voltages. Electrochemical strain microscopy allowed probing of the changes in local electrochemical activity during the pre-forming and forming stages. The associated structural changes were visualized by transmission electron microscopy. The results allowed an understanding of the electrochemical processes in the early stages of electroforming, and provide a comprehensive approach for exploring irreversible and partially reversible bias-induced transformations in solids.