Fig. 3.

Oxygen ion evolution at Co/SrCoO_2.5 interfaces. a Cross-section low-resolution TEM image of the device structure, in which the scale bar is 50 nm. HRTEM image of Co/SrCoO_2.5 heterointerface at (b) the pristine state and (c) the high-resistance state. The disordered SrCoO_2.5+δ region could be clearly identified as compared with the pristine state, as shown in the magnified image (d). e HRTEM image of the Co/SrCoO_2.5 interface in the low-resistance state with the observation of conducting filaments (highlighted by the blue areas). The red and yellow areas denote the remaining disordered and pristine regions, respectively. f Detailed crystalline structure at the conducting filament, which are composed of ordered SrCoO_2.5−δ with pronounced oxygen vacancies (V_O). The insets of (b), (d), and (f) show the diffraction patterns obtained by local FFT. g Schematic diagram of the oxygen ion evolution with the corresponding band alignments at the heterointerface. h Comparison of Co L-edge EELS spectra of the disordered area and the conducting filament at the interface, as well as the bulk region of the SrCoO_2.5 layer. The L₃ peak values of the filaments, pristine and disordered regions are 771.2, 771.5, and 771.7 eV, respectively. The scale bar indicates 5 nm in (b), (c) and (e) and 2 nm in (d) and (f)