Regensburg 2016 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 8: Surface State Spectroscopy I

O 8.8: Vortrag

Montag, 7. März 2016, 12:30–12:45, H4

Polaron driven structural reconstruction in Rutile TiO₂(110) — •Michele Reticcioli¹, Xianfeng Hao², Martin Setvin³, Ulrike Diebold³, and Cesare Franchini¹ — ¹University of Vienna — ²Yanshan University — ³Vienna University of Technology

The role of polarons in TiO₂ is of key importance for understanding the fundamental properties and functionalities of this material. In this work we use density functional theory with an on-site Coulomb interaction U and molecular dynamics to study the formation and dynamics of small polarons in the reduced rutile TiO₂(110) surface. Our theoretical results are validated by a direct comparison with STM data. We show that excess electrons donated by oxygen vacancies (V_O) form small polarons preferentially in subsurface Ti sites, and that polarons easily hop to neighboring sites in the subsurface and surface layers. The polaron stability (in terms of the polaron formation energy) has been examined as a function of V_O concentration (5.5%, 11%, 16.6% and 22.2%) by adopting a large (9×2) supercell. It is found that polaron formation become more favorable by increasing V_O concentration due to the lower energy cost to distort the lattice, which is needed to provide the lattice with the necessary flexibility to host self-trapped electrons. At high polaron concentration the polaron-polaron repulsion weakens this trend and drives the system towards an instability, falling into a reconstruction of the surface. The polaron driven surface reconstruction has been studied for two particular suggested structures, named Ti₂O₃-(1×2) and Ti₂O-(1×2). Hence the convenience of the reconstruction with respect to the thermodynamic conditions has been clarified.