Single-layer TiO_x reconstructions on SrTiO₃ (111): (√7 × √7)R19.1° (√13 × √13)R13.9° and related structures

The atomic structures of two reconstructions, (√7 × √7)R19.1° and (√13 × √13)R13.9° on the SrTiO₃ (111) surface were determined using a combination of density functional theory and scanning tunneling microscopy data and APW + lo density functional theory minimizations and simulations. These reconstructions belong to the same structural family made up of an interconnected, single layer of edge-sharing TiO₆ and TiO₅ octahedra. This family of reconstructions between 0.5 and 1.5 excess TiO₂ representing the lowest-reported TiO₂ coverages for reconstructions on this surface. This family is found to include the previously-solved (2 × 2)a reconstruction. They all follow a simple rule for surface composition, which serves as a tool for better understanding and predicting the structure of other reconstructions of arbitrary surface unit cell size on SrTiO₃ (111). This reconstruction family and the calculations of surface energies for different hypothesis structures also shed light on the structure of Schottky defects observed on these reconstructed SrTO₃ (111) surfaces.