Correlation of H Adsorption Energy and Nanoscale Elastic Surface Strain on Rutile TiO₂(110)

Scanning tunneling microscopy (STM) has been used to obtain the aerial distribution of bridge-bonded hydroxyl groups (HO_b) on a rutile TiO₂(110) surface, modified with a well-defined nanoscale strain field. Our study makes use of earlier findings that 5–30 nm wide locally strained areas of the surface can be formed via low-energy Ar-ion bombardment combined with a thermal treatment. These strained areas appear as protrusions in the STM images, resulting from subsurface argon-filled cavities. Our STM images show that the local surface concentration of OH_b groups is lower on the protrusions. This lowering of concentration has been interpreted as a reduction in the local H absorption energy, Δ<i>E</i>, a result similar to that observed on metals. In this paper, analysis of the reduction in this O–H bond energy across the surface shows a strong correlation between Δ<i>E</i>_OH and the characteristic surface strain value, <i>S</i>. The Δ<i>E</i>_OH values have been calculated through a subtraction of the contribution of the repulsive dipole–dipole interaction between OH_b groups. This interaction has been estimated from an analysis of the radial distribution of OH_b pairs in the STM images. The measured linear relation between the reduction in O–H bond energy and the surface strain has been estimated to be Δ<i>E</i>_OH (meV) ≈ 11·<i>S</i> (%)