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Atomic and Electronic Structure of the BaTiO(001) (√5 x √5) R26.6 Surface Reconstruction

figureUsing both experimental scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements, we were able to further narrow down the candidate structures, and conclude that the surface is either TiO2 –Ti3/5, TiO2 –Ti4/5 , or some combination, where Ti adatoms occupy hollow sites of the TiO surface. DFT indicates that the defect states close to the valence band are from Ti adatom 3d orbitals (≈1.4 eV below the conduction band edge) in agreement with STS measurements showing defect states 1.56 ± 0.11 eV below the conduction band minimum (1.03 ± 0.09 eV below ).  STM measurements show electronic contrast between empty and filled states images. The calculated local density of states at the surface shows that Ti 3d states below and above explain the difference in electronic contrast in the experimental STM images by the presence of electronically distinctive arrangements of Ti adatoms. This work provides and interesting contrast with the related oxide SrTiO, for which the (001) surface reconstruction is reported to be the TiO surface with Sr adatoms.