Fig. 4

Submolecular-resolution AFM images of weakly bonded water clusters with a CO-tip. a–d Geometric structures, experimental STM images, experimental and simulated Δf images of two water dimers, respectively. The crooked depressions in the AFM images are highlighted by dashed lines in a, c, and d. Set point of b: 100 mV and 50 pA, 30 pA, 25 pA (from left to right), respectively. The tip height of c is 100 pm, 100 pm, and 130 pm (from left to right), respectively. e–h Geometric structures, experimental STM images, experimental and simulated Δf images of three water trimers, respectively. Set point of f: 100 mV and 25 pA, 20 pA, 15 pA (from left to right), respectively. The tip height of g is 130 pm, 130 pm and 110 pm (from left to right), respectively. All the oscillation amplitudes of experimental and simulated images are 100 pm. All the simulations were done with a quadrupole (\({d}_{{\mathrm{z}}^2}\)) tip (k = 0.5 N m⁻¹, Q = −0.2 e). The images of the first two dimers were obtained with the same CO-tip, while the third dimer was measured with a different CO-tip at a different site. The three trimers were imaged at different sites with different CO-tips. Size of the images: 1.2 nm × 1.2 nm