Extended Data Fig. 11: Electrical measurements of insulating AMC samples.

a, Optical images of as-fabricated AMC devices with the sample highlighted by dashed blue lines. b, Two-terminal I–V curves with a bias sweep from −10 V to 10 V. AMC samples from zone III, including AMC-325, AMC-350, AMC-375 and AMC-400, show <2 pA of the current, comparable with that from the bare SiO₂ substrate, strongly suggesting the highly insulating behaviours. By contrast, AMC-450 from zone IV manifests an almost linear current response. We note that we treat this I–V curve of AMC-450 (the normal linear response to applied voltage but with the lowest current in all AMC devices) as the detection limit of our instruments for the AMC system. c, Temperature-dependent I–V curves for AMC-350, showing no increase of the current at elevated temperatures. d, Raman mapping of the sum of G and D peaks (in area), corresponding to the channel region of the AMC-350 device marked by the dashed red lines in the top-middle panel of a, demonstrating the continuity of AMC across two electrodes. e,f, Atomic force microscopy results of the AMC-375 channel area (indicated by the dashed red line in the top-right panel of a) in height (e) and phase (f), both showing the absence of any apparent structural cracks or holes. By confirming the AMC continuity in the device channel from the Raman and atomic force microscopy characterizations, we conclude that AMC samples from zone III are indeed electrically insulating with the comparable level with SiO₂, or at least in the limit of our instruments. Scale bars, 20 μm (a), 5 μm (d–f).