Fig. 2.

Operando TEM studies showing the formation of conductive filament. (A and B) HAADF image and schematic diagram of the experimental setup of the VO₂ device. Each FIB sample has three vertical cuts, making two out-of-plane devices. (C) Experimental image and the corresponding schematic of the conductive filament. (D) SAED acquired from the conductive filament area. (E) Dark-field image using the diffraction spot marked by red circle ((001) of V₅O₉) in D. (F) Core-loss EELS for VO₂ and V₅O₉. Approximately 0.15-eV energy shift is found for the V₅O₉.