Paper NS-WeM11
Controlling Surface Reactivities of TiO₂ (110) by Nanoscale Strain Field

Wednesday, November 12, 2014, 11:20 am, Room 304

Strain is found to be an ubiquitous quantity in nanostructured surfaces and on supported catalysts. Therefore, understanding the influence of strain on surface properties is crucial for rational design of catalytic materials. The study of the interaction of nanoscale strain and adsorbate reactivity presents two experimental challenges, generating an intense strain field and differentiating strain effects from effects induced by change in other surface properties. In this work, we generate a patterned, nanoscale strain field on TiO₂ (110) surface by low energy bombardment of single crystal TiO₂ samples with argon ions at 1000^oC. The interstitial argon diffuses so as to self-assemble into highly pressurized argon clusters and distort the surrounding lattice a few nanometers below the surface. As a result, the top surface layers of the crystal have a convex morphology while retaining their unstressed surface structures, thus introducing nanometer-size surface protrusions . The strain level obtained on the protrusions can be as large as ~4%. The locally varying strain field across the protrusion is ideal for strain effects study. By combining scanning tunneling spectroscopy (STM) imaging and continuum model, we show that the adsorption energy of hydrogen binding to surface bridge-bonded oxygen (BBO) is significantly altered by local lattice strain. In particular, strain causes, oxygen vacancies (BBOv) to be absent from the strained area. Our results thus provide direct evidence of the influence of strain on atomic-scale surface properties and thus help guide future research in catalysis materials design