Interplay between adsorbates and polarons: CO on rutile TiO$_2$(110)

TL;DR

This study investigates how polarons influence CO adsorption on rutile TiO₂(110) surfaces, revealing that polaron interactions depend on surface reduction state and significantly affect adsorption configurations.

Contribution

It combines first principles calculations with STM/AFM experiments to elucidate the interaction mechanisms between polarons and CO molecules on TiO₂(110).

Findings

CO shows attractive coupling with surface polarons and repulsive with subsurface polarons.

Adsorption configurations vary with surface reduction, with dominant modes at oxygen vacancies and Ti sites.

Polaron presence influences the preferred adsorption sites and energies.

Abstract

Polaron formation plays a major role in determining the structural, electrical and chemical properties of ionic crystals. Using a combination of first principles calculations and scanning tunneling microscpoy/atomic force microscopy (STM/AFM), we analyze the interaction of polarons with CO molecules adsorbed on the rutile TiO$_2$(110) surface. Adsorbed CO shows attractive coupling with polarons in the surface layer, and repulsive interaction with polarons in the subsurface layer. As a result, CO adsorption depends on the reduction state of the sample. For slightly reduced surfaces, many adsorption configurations with comparable adsorption energies exist and polarons reside in the subsurface layer. At strongly reduced surfaces, two adsorption configurations dominante: either inside an oxygen vacancy, or at surface Ti$_{5c}$ sites, coupled with a surface polaron.