The common ways to activate a chemical reaction are by heat, electric current, or light. However, mechanochemistry, where the chemical reaction is activated by applied mechanical force, is less common and only poorly understood at the atomic scale. Here we report a tip-induced activation of chemical reaction of carbon monoxide to dioxide on oxidized rutile TiO₂ (110) surface. The activation is studied by atomic force microscopy, Kelvin probe force microscopy under ultrahigh-vacuum and liquid nitrogen temperature conditions, and density functional theory (DFT) modeling. The reaction is inferred from hysteretic behavior of frequency shift signal further supported by vector force mapping of vertical and lateral forces needed to trigger the chemical reaction with torque motion of carbon monoxide towards an oxygen adatom. The reaction is found to proceed stochastically at very small tip-sample distances. Furthermore, the local contact potential difference reveals the atomic-scale charge redistribution in the reactants required to unlock the reaction. Our results open up new insights into the mechanochemistry on metal oxide surfaces at the atomic scale.

Probing CO at a specific site on a metal oxide surface is essential for characterizing various applications such as CO oxidation, hydrogenation, and water–gas shift reaction. Herein, we use atomic force microscopy and Kelvin probe force microscopy to probe the CO on a rutile TiO₂(110) surface. Our results indicate that CO can be manipulated along the Ti row by the repulsive lateral force of “pushing” mode. Furthermore, the joint combination of precise manipulation and the distance dependence of local contact potential difference allow us to resolve the interatomic dipole moment and charge state of CO at atomic resolution. Therefore, we found that the negatively charged CO with the dipole moment of negative pole down on the rutile TiO₂(110) surface. Our results suppose that both the charge state as well as the on-surface dipole interaction are very effective for CO reaction on rutile TiO₂(110) surface.