Fig. 3: Physical mechanism of highly mobile Cu⁺ ions-meditated current rectification.

a Schematic static band configuration for tip/CIPS/Au bottom electrode measurement setup according to the work function of Pt/Ir tip (5.6 eV)⁴², Au (5.1 eV)⁴³, and electron affinity of CIPS (3.7 eV)⁴⁴. The difference in the work function/electron affinity creates asymmetric interfaces, with the Schottky barrier φ₁ and φ₂ at the side of Pt/Ir tip and the bottom Au electrode, respectively; b In the absence of Cu⁺ ions migration, the schematic electrons (cyan balls) transport process in different bias direction, where the bias voltage is applied to the bottom Au substrate; c, d Cu⁺ ions (blue ball) undergo directional migration driven by the applied voltage. e, f In the presence of Cu⁺ ions migration and redistribution, the schematic Cu⁺ ions (blue balls) migration and electrons (cyan balls) transfer for current flow. g–i The topography image in virgin state, after two consecutive positive voltage sweeping semi-cycle (0 V→+4 V→0 V), and after two consecutive negative voltage sweeping semi-cycle (0 V→−4 V→0 V), respectively. The I–V measurements are conducted in the white square area in g–i and the ever-present bump in the mark location rules out the possibility of tip scraping for the bump elimination during scanning. The scale bar length is 200 nm in g–i.