Fig. 2
The role of electrostatics in the high-resolution AFM imaging of a water tetramer. a–d Simulated AFM images of a water tetramer with neutral, s, pz and \({d}_{{\mathrm{z}}^2}\) tip models, respectively (k = 0.5 N m−1, Q = −0.2 e). The first, second, and third rows correspond to the images acquired at the tip heights of about z1 = 7.9 Å, z2 = 6.8 Å and z3 = 6.4 Å, respectively. For a better comparison, we had chosen similar simulation images by subtracting a small offset of tip height between different tips. The tip height is defined as the distance between the outmost metal atom of the tip and the upward H atom of the water tetramer. The oscillation amplitude of all the simulated Δf images is 100 pm. The size of the images is 1.2 nm × 1.2 nm. e Simulated force curve of the water tetramer taken with the \({d}_{{\mathrm{z}}^2}\) tip, where the three tip heights (z1, z2, and z3) are denoted. The tip position is indicated by a star in d. f Charge distribution of the CO-tip from DFT calculations. g Maps of calculated vertical electrostatic forces between the sample and different tip models (s, pz and \({d}_{{\mathrm{z}}^2}\)) computed by convolution of Hartree potential of sample and model charge distribution on the tip39
