Description
The role of polarons is of key importance for the understanding of the fundamental properties and functionalities of TiO$_2$.We use density functional theory with an on-site Coulomb interaction and molecular dynamics to study the formation and dynamics of small polarons in the reduced rutile (110) surface, as reported in our recent publication~\cite{PhysRevX.7.031053}.We show that excess electrons donated by oxygen-vacancies (V$_{\rm{O}}$) form mobile small polarons that hop easily in subsurface and surface Ti-sites.The polaron formation becomes more favorable by increasing the V$_{\rm{O}}$ concentration level (up to ~20\%) due to the progressively lower energy cost needed to distort the lattice.However, at higher V$_{\rm{O}}$ concentration the shortening of the averaged polaron-polaron distance leads to an increased Coulomb repulsion among the trapped charges at the Ti-sites, which weakens this trend.This instability is overtaken by means of a structural $1\times2$ surface reconstruction, characterized by a distinctively more favorable polaron distribution.The calculations are validated by a direct comparison with experimental AFM and STM data.Our study identifies a fundamentally novel mechanism to drive surface reconstructions and resolves a long standing issue on the origin of the reconstruction in rutile (110) surface.| Period | 19 Mar 2018 |
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| Event title | School on Electron-Phonon Physics from First Principles |
| Event type | Summer/Winter school |
| Location | Trieste, ItalyShow on map |
Keywords
- electon-phonon coupling
- polaron