Extended Data Fig. 3: I-V characteristics of 1 and 2.

Current versus time histograms for 1 (a) and 2 (b). In each histogram, the top panel is the bias applied across a 100 kΩ resistor in series with the junction while the tip-substrate distance is held constant. Current is logarithmically-binned (57 bins dec⁻¹) and time is linearly binned (4000 bins s⁻¹). Histogram (a) compiled from 242/1200 selected traces with ± 1.8 V maximum applied bias. Histogram (b) compiled from 389/2000 selected traces with ± 2.0 V maximum applied bias. Number of counts increases from red to yellow. Note: Since the maximum applied bias for 1 is only ± 1.8 V, the hold time is shortened to maintain the same voltage sweep rate.