Fig. 3: Elucidating H-bonding directionality and proton ordering in a hexamer.
a–c Bond-resolved AFM image (a), DFT-optimized structure (b), and proton-order-resolved AFM image (c) of the –8.5°–L hexamer on Ag(111). d, f Simulated AFM images at z’ = 4.40 Å (d) and z’ = 5.10 Å (f). e, Electrostatic potential map at 1.52 Å above the topmost atoms corresponding to (b). g Experimentally obtained Fmin(d) curves (black solid dots) for six H-bonds, ordered clockwise (dashed arrow in a). Red and blue curves are site-dependent F(z) spectra taken at two peak positions. h Concatenated simulated Δfmin(d) profiles along six H-bonds, corresponding to colored arrows in (d). i, j Zoom-in of a representative Δfmin(d) profile showing two maxima (i), and simulated ∆f(z) spectra at the N and NH sites extracted at those maxima (j). Experimental AFM images were recorded at z = −30 pm (a) and z = 25 pm (c) relative to the STM setpoint (Us = 20 mV, It = 5 pA) above Ag(111). Orange shading in (g) marks H-bonds assigned as non-classical. AFM imaging heights (experimental and simulated) in (a, c, d, f) are indicated by dashed lines in the corresponding force-spectroscopy plots (g, j). Source data are provided as a Source Data file.
