Figure 1: Ti L-edge XPEEM analysis of SrTiO₃ memristive devices.

(a) Device schematic. (b) Representative I–V curve. (c) Retention behaviour of different devices on the same chip. Devices RESET into the HRS remain at a constant resistance over several days (violet curve). Devices that were SET into the LRS show two classes of retention behaviour: stable retention and retention failure (red and blue curves, respectively). For each class of retention behaviour, the resistance was averaged for five representative devices. Error bars indicate the minimum and maximum values obtained for each resistance state. (d) XPEEM image of a device with a stable retention recorded with a photon energy of 458.5 eV. Filament indicated by a red arrow. Scale bar, 2 μm. (e) Ti L-edge spectra extracted from the XPEEM image stack for a region inside the bright filament discernable in d (red line) and for the surrounding device area (blue line). The dotted line and the dashed line denote the e_g level of the Ti L₃ edge in Ti⁴⁺ and Ti³⁺ configuration, respectively. (f) False colour map of the Ti³⁺ contribution for the device in d. Only within the suspected switching filament, there is a significant spectral contribution of Ti³⁺. The enhanced contrast surrounding the active device is caused by the reactive ion beam etching involved in the electrode structuring and is not associated with the device conductance. (g) XPEEM image of a device with retention failure recorded with a photon energy of 459.5 eV. (h) Ti L-edge spectra extracted from the XPEEM image stack for a region inside the suspected switching filament discernable in g (red line) and for the surrounding device area (blue line). (i) False colour map of the Ti³⁺ spectral contribution for the device in g. No Ti³⁺ contribution is discernible for the entire device area.