Extended Data Fig. 3. Meniscus-surface contact.

a, Schematic of the approach and retract stages for our scanning protocol. b, Example of I_dc - t characteristics (ion current between the two electrodes in the nanopipette) for proton conducting (blue) and non-conducting (red) areas in a graphene device. c, Map showing changes in I_dc during step ii with respect to the current in step i (ΔI_dc = $I_{\mathrm{dc}}^{\mathrm{ii}}$ − $I_{\mathrm{dc}}^{\mathrm{i}}$) for the graphene device in b. d, Map of ΔI_dc = $I_{\mathrm{dc}}^{\mathrm{iii}}$ − $I_{\mathrm{dc}}^{\mathrm{i}}$ for the same device. e–g, Same as in panels b–d but for a monolayer hBN device. Scale bars, 1 μm.