Dresden 2020 – scientific programme
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O: Fachverband Oberflächenphysik
O 20: Oxides II: Structures, Interactions and Reducibility
O 20.2: Talk
Monday, March 16, 2020, 15:45–16:00, WIL B321
Direct Assessment of the Proton Affinity of Individual Surface Hydroxyls with AFM and DFT — •Bernd Meyer1, Margareta Wagner2, Martin Setvin2, Michael Schmid2, and Ulrike Diebold2 — 1Interdisciplinary Center for Molecular Materials and Computer-Chemistry-Center, FAU Erlangen-Nürnberg, Germany — 2Institute of Applied Physics, TU Wien, Austria
The state of protonation/deprotonation of individual surface sites has far-ranging implications in all areas of chemistry. However, common experimental measurements of surface acidity are integral techniques which give only average quantities integrated over the whole surface. Here we show that an OH-functionalized tip of an atomic force microscope (AFM) can be used for quantitative insights into the acidity of individual surface OH groups. The chosen model oxide, In2O3(111), offers four types of surface O atoms with distinct properties, each giving rise to a characteristic force–distance curve after protonation. Density-functional theory (DFT) calculations demonstrate a linear correlation between the force minimum and the proton affinity of the surface hydroxyls. By benchmarking the calculations to known proton affinities and pKa values of gas-phase molecules, the force minima provide a direct measure of proton affinity distributions and pKa differences at the atomic scale.