Extended Data Fig. 3: Adsorption sites of OH groups on In₂O₃(111).

a–f, Constant-height nc-AFM images of three dissociated water molecules in adjoining unit cells, taken with decreasing tip height. The height difference ∆z between the subsequent images is 10 to 15 pm. Each dissociated water molecule gives rise to two OH groups adsorbed next to each other, O_WH and O_SH (where the ‘W’ and ‘S’ indicate the origin of the oxygen atom, that is, the water molecule or the surface, respectively)²⁵. In a, with the tip farthest away, both OH groups are imaged as dark features. As the tip comes closer to the OH groups (b, c), the O_WH (sticking farther away from the surface than the O_SH) turn bright (onset of repulsive interaction, but overall attractive forces). In d, the O_SH also start to be imaged as bright features. Approaching the surface even more, e, f reveal the O(3c) lattice atoms of the surface; this information was used to determine the adsorption sites of the OH groups experimentally. g, Profiles of the frequency shift across the O_SH and O_WH pair as indicated by the arrows in a–f. h, Same image as f with the O(3c) lattice superimposed (O(α), white; O(β), red; O(γ), orange; O(δ), yellow). The site of the O_SH is identified as an O(β) (circle filled black). i, Atomic model of the surface including the adsorption sites of the O_SH and O_WH (black circle, filled white), which bridges two In(5c) atoms nearby. The adsorption sites agree with previous STM and DFT results in ref. ²⁵.