Extended Data Fig. 7: Transferability and reproducibility of the method.
From: Direct assessment of the acidity of individual surface hydroxyls
F(z) curves on OSH/TiO2(110) and OH/zirconium oxide/Pt3Zr(0001) obtained with the OH-terminated indium oxide tip. a, TiO2(110): experimental data. The tip was prepared on hydroxylated In2O3(111), and F(z) curves were taken on the OWH and OSH(β) (labelled as such) to ascertain the tip termination (fR = 69.6 kHz, k = 5,400 N m−1, A = 60 pm). For reference, the curves from the main text (Fig. 2) are also plotted on the left; for better visibility they are shifted horizontally by −2 Å. This tip was used to obtain the F(z) curve on OSH/TiO2(110) (brown, shifted to the right). Approaching the OSH on TiO2 even closer results in picking up the H. The hydroxylated TiO2(110) surface was prepared following a well established procedure26, which results in one type of hydroxyl at a bridging O(2c) atom. b, Calculated short-range F(z) curves on bridging hydroxyls on TiO2(110) for two OH coverages (1/4 and 1/8 monolayer) obtained with the OH-terminated InOx tip. c, Zirconium oxide: the standard tip was prepared on hydroxylated In2O3(111), and F(z) curves were taken on the OWH and OSH(β) (labelled as such) to ascertain the tip termination. For reference, the curves from the main text (Fig. 2) are also plotted on the left; for better visibility they are shifted horizontally by −2 Å. This tip was used to take F(z) curves on hydroxylated zirconium oxide (purple, shifted to the right). d, Zirconium oxide: the same type of measurement, but with an unknown tip termination that gives more shallow minima for OWH and OSH on hydroxylated In2O3(111). Note that both tips measure the same relative positions in the force minima of the strongly bound H on In2O3(111) and zirconium oxide, that is, the force on OH/zirconium oxide lies between OWH and OSH(β) (fR = 77.2 kHz, k = 5,400 N m−1, A = 240 pm (In2O3), 250 pm (zirconium oxide)). The ultrathin zirconium oxide layer was prepared following the method of ref. 30. The surface was exposed to 2 langmuir (1 L = 1.33 × 10−6 mbar s) of water at 320 K.
