Figure 1: Imaging of dynamic ion accumulation during resistance switching process.

(a) Schematic of the conductive atomic force microscopy (C-AFM) measurements on HfO₂/TiN samples. (b) Schematic of the electrostatic force microscopy (EFM) measurements on HfO₂/TiN samples. (c) Topographic image showing the locations where voltage sweepings with different amplitudes were performed. Scale bar, 4 μm. (d–g) Electrical (d), topographic (e), 1ω (f) and 2ω (g) measurements on the region stimulated by voltage sweeping up to 5 V during preceding C-AFM measurements. Scale bar, 200 nm. (h–k) Corresponding electrical and EFM results on the region stimulated by voltage sweeping up to 6 V during preceding C-AFM measurements. Scale bar, 200 nm. (l–o) Corresponding electrical and EFM results on the region stimulated by voltage sweeping up to 8 V during preceding C-AFM measurements. Scale bar, 200 nm. (p–s) Corresponding electrical and EFM results on the region stimulated by voltage sweeping up to 10 V during preceding C-AFM measurements. Scale bar, 200 nm.