Fig. 3
Experimental and simulated AFM images of two degenerate water tetramers with a Cl-terminated tip. a, f Derivative STM images of the water tetramers with clockwise and anticlockwise hydrogen-bonded loops, respectively. Set point: 10 mV and 50 pA. b–d, g–i Corresponding Δf images. All the images were obtained on the same tetramer (switched) with the same Cl-tip. The tip heights are 30 pm (b, g), −120 pm (c, h), −120 pm (d, i). The oscillation amplitudes are 40 pm (b, g), 100 pm (c, h), 40 pm (d, i). The “fork-like” features are denoted by two green arrows in c and h. It is noted that the smallest tip heights for the AFM imaging here are at least 20 pm larger than those for the perturbative chirality switching in ref. 15. e, j Simulated Δf images with the oscillation amplitudes of 40 pm, which were obtained with a monopole (s) tip (k = 0.5 N m−1, Q = −0.25 e). The size of the images is 1.2 nm × 1.2 nm
