Structural model of the surface: (a) Side view and (b) top view of vacancy and OH defects on . White and red balls indicate the in-plane oxygen and titanium atoms, respectively. Bridging oxygen atoms are represented as yellow balls. Arrows indicate an vacancy site, OH site, and different Ti sites discussed in the text. The numbering of sites is with respect to the vacancy defect.
Constant current STM images of surface kept in the preparation chamber for several minutes (; ) at 78 K. (a) Before and (b) after scanning with ; . Arrows indicate an oxygen vacancy and two OH impurities, which are removed by the high-bias scanning procedure.
Constant current STM images of the at 78 K. (a) Unoccupied state image (; ) is observed in forward scanning, and (b) occupied state (; ) in reverse scanning. The expanded images around an vacancy (yellow rectangles) of (a) and (b) are also shown. Red open circles indicate the positions of vacancies.
STS (inset) and measurements of the position dependent occupied DOS at a vacancy . (a) Measurements are taken at the center of a lobe in the occupied STM image (between the and sites); (b) at a site and (c) at the vacancy site. The measured sites are indicated in the occupied-state STM image. The set-point values of and were fixed at and 1.0 nA. Dots and lines show the raw and smoothened data, respectively.
(a) An unoccupied ( and ), and (b) occupied state images ( and ) of vacancy and OH on (size: ) captured side by side in the USTC experiment . The high contrast images of the (c) OH impurity and (d) vacancy defects showing the characteristic similarities (delocalization along rows) and differences (shuttle vs four-lobed shape).
The structure and the orbital distribution of defect states of 25% density of vacancy defects on surface. The smaller unit cell than in Fig. 7 helps to visualize how the defect formation affects the lattice structure and the orbital distribution (blue translucent structures). The gray and red balls indicate the Ti and O atoms, respectively. The coordinate axes at the and sites are defined in (a) and (b), respectively. [(c) and (d)] The side views, and [(e) and (f)] the top views of an vacancy defect before [left: (a), (c), and (e)] and after [right: (b), (d), and (f)] the structural optimization. The local coordination of and ions defines the -, -, and -axes. The -axis is directed toward the vacancy and the surface normal for and , respectively.
The simulated STM images of surface with 10% vacancy density at (a) before, (b) after structure optimization, and (c) at after structure optimization for the vacancy creation. White and black circles indicate the positions of the vacancies and ions, respectively.
The structure, orbital distribution and STM image of 8.3% OH defect density (a) The structure of OH impurity optimized by PW91. (b) The orbital distribution of OH induced defect states, and simulated STM image at (c) and (d) for OH on surface.
Different optimized structures and spatial orbital distributions obtained by the [(a)–(e)] polarized B3LYP and [(f)–(j)] PW91 calculations. The gray and red balls indicate Ti and O atoms. The pink circle locates the vacancy defect. The dashed line defines a symmetry plane normal to the surface. (a) The asymmetric structure with respect to the symmetry plane obtained by B3LYP. Selected Ti–O bond lengths in the surface plane are given. (b) The corresponding asymmetric orbital distribution of the defect states. (c) The corresponding asymmetric orbital distribution of the unoccupied states in the energy range of 0–10 eV. The simulated STM image at (d) and (e) using asymmetric structure. (f) The symmetric structure obtained by PW91. (g) The corresponding symmetric orbital distribution of the defect states. (h) The corresponding symmetric orbital distribution of the unoccupied states in the energy range of 0–10 eV. The simulated STM image at (i) and (j) using symmetric structure.
The calculated total DOS. (a) The DOS for the perfect surface obtained by PW91 using the PW91 (symmetric) structure. (b) The DOS of the 25% defective surface obtained by B3LYP using the PW91 (symmetric) structure. (c) The DOS of the 25% defective surface obtained by B3LYP using the B3LYP (asymmetric) structure. The zero energy is set to the VBM.
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