Quantum surfaces: polaron quasiparticles interact with CO


The Quantum Materials Modelling group (C. Franchini) in collaboration with the experimental surface science group at TU Wien (U. Diebold) have shown that quantum effects play a decisive role in the adsorption of molecule on surfaces. The results have been published in the APS journal "Physical Review Letters".

Interplay between Adsorbates and Polarons: CO on Rutile TiO2(110)

Polaron formation plays a major role in determining the structural, electrical, and chemical properties of ionic crystals. Using a combination of first-principles calculations, scanning tunneling microscopy, and atomic force microscopy, we analyze the interaction of polarons with CO molecules adsorbed on the reduced rutile TiO2(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 dominate: either inside an oxygen vacancy, or at surface Ti5c sites, coupled with a surface polaron. Similar conclusions are predicted for TiO2(110) surfaces containing near-surface Ti interstitials. These results show that polarons are of primary importance for understanding the performance of polar semiconductors and transition metal oxides in catalysis and energy-related applications.

M. Reticcioli, I. Sokolović, M. Schmid, U. Diebold, M. Setvin, and C. Franchini

"Interplay between Adsorbates and Polarons: CO on Rutile TiO2(110)",

Phys. Rev. Lett. 122, 016805 (2019)

DOI: https://doi.org/10.1103/PhysRevLett.122.016805



Effects of a CO molecule adsorbed at NNN−Ti5c site on polaronic states at low reduction level (5.6%, i.e., one VO in a 9×2 two-dimensional unit cell). (a) and (b) electronic charge density of the S1 (a) and S0 (b) polarons in presence of CO. Atoms at the back are depicted by bleached spheres. A top view of the considered configuration is also sketched in each panel. The insets represent the experimental and simulated filled-state STM images. (c) Polaron formation energy of S0 and S1 polarons, in case of a TiO2(110) surface with and without adsorbed CO